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Electronics => Projects, Designs, and Technical Stuff => Topic started by: tatus1969 on June 14, 2017, 07:16:01 AM

Title: kWeld - "Next level" DIY battery spot welder
Post by: tatus1969 on June 14, 2017, 07:16:01 AM
I have received parts for a small project that I haven't found realized in the way that I am attempting it. For today, just a picture. That AWG8 cable assembly took me two hours to finish :o

Any creative idea of what this is going to become in the end? ;)

(http://www.eevblog.com/forum/projects/guesses-on-what-i-am-attempting-here/?action=dlattach;attach=323717)
Title: Re: Guesses on what I am attempting here?
Post by: Paul Price on June 14, 2017, 07:38:57 AM
A waste of time.
Title: Re: Guesses on what I am attempting here?
Post by: Paul Price on June 14, 2017, 07:41:52 AM
2nd Guess: Remote voltage sensing also incorporating a fused power connection.
Title: Re: Guesses on what I am attempting here?
Post by: CM800 on June 14, 2017, 07:49:37 AM
Depends... what is that black brick?

if it's a FET... coilgun! :D
Title: Re: Guesses on what I am attempting here?
Post by: Electro Detective on June 14, 2017, 08:54:36 AM
Some sort of payback device for a Neighbors From Hell electrical switchboard ?  >:D

 :popcorn:
Title: Re: Guesses on what I am attempting here?
Post by: MK14 on June 14, 2017, 09:04:25 AM
You using a PMSM servo motor, at 2,000 Watts (we are!), to stack an extra third road traffic cone, on top of two nicely stacked on top of each other ?
Title: Re: Guesses on what I am attempting here?
Post by: buck converter on June 14, 2017, 09:23:34 AM
welder?
Title: Re: Guesses on what I am attempting here?
Post by: Koen on June 14, 2017, 09:29:19 AM
A very-rugged armband for your smartphone ?
Title: Re: Guesses on what I am attempting here?
Post by: MK14 on June 14, 2017, 09:35:04 AM
48V, 40 Amp, Connector to a/the Motor (controller elsewhere), 2,000 Watt. With directional control, the black, four terminal block being some kind of powerful diode block/pack.
Title: Re: Guesses on what I am attempting here?
Post by: blueskull on June 14, 2017, 09:52:39 AM
Spot welder.
Title: Re: Guesses on what I am attempting here?
Post by: mjkuwp on June 14, 2017, 09:52:52 AM
To me it looks like a hookup for  a power meter, but that is not a creative idea on my part : (
Title: Re: Guesses on what I am attempting here?
Post by: StillTrying on June 14, 2017, 09:53:19 AM
Remote switch off.
Two pin power connector tester, because that looks like it would be the first part to blow!
Title: Re: Guesses on what I am attempting here?
Post by: BrianHG on June 14, 2017, 10:47:09 AM
A solar battery charger/inverter switch.
Title: Re: Guesses on what I am attempting here?
Post by: P90 on June 14, 2017, 10:58:12 AM
2 hours?
You're fired!   :-DD
Title: Re: Guesses on what I am attempting here?
Post by: Electro Detective on June 14, 2017, 12:26:56 PM
2 hours?
You're fired!   :-DD

Time flies when you want to make sure it's done right  :-+

The picket lines will be in place tomorrow morning :rant: :box: :blah: :bullshit: :clap: unless he gets his job back   

Any cheap scab labor trying to get past may experience an accident    >:D

Title: Re: Guesses on what I am attempting here?
Post by: P90 on June 14, 2017, 12:39:10 PM
2 hours?
You're fired!   :-DD

Time flies when you want to make sure it's done right  :-+

The picket lines will be in place tomorrow morning :rant: :box: :blah: :bullshit: :clap: unless he gets his job back   

Any cheap scab labor trying to get past may experience an accident    >:D


must be union... :palm:
Title: Re: Guesses on what I am attempting here?
Post by: macona on June 14, 2017, 03:20:22 PM
I think I would be using anderson power poles instead of RC car connectors.

And 2 hours??? How?
Title: Re: Guesses on what I am attempting here?
Post by: tatus1969 on June 14, 2017, 03:22:45 PM
Some sort of payback device for a Neighbors From Hell electrical switchboard ?  >:D

 :popcorn:
That must be really a switchboard right from hell if it uses Deans T connectors  >:D
Title: Re: Guesses on what I am attempting here?
Post by: tatus1969 on June 14, 2017, 03:24:09 PM
You using a PMSM servo motor, at 2,000 Watts (we are!), to stack an extra third road traffic cone, on top of two nicely stacked on top of each other ?
:-DD you're well informed, but not even close ;)
edit: except for one part: resistance is supposed to be futile in this case as well 8)
Title: Re: Guesses on what I am attempting here?
Post by: tatus1969 on June 14, 2017, 03:26:13 PM
I think I would be using anderson power poles instead of RC car connectors.

And 2 hours??? How?
The connector scares worries me a bit too, but the counterpart is already there...
Title: Re: Guesses on what I am attempting here?
Post by: tatus1969 on June 14, 2017, 03:33:24 PM
2 hours?
You're fired!   :-DD
I should have quit that job because of poor working conditions! The crimp tool didn't take the AWG8 without adding a hammer, the soldering iron didn't like that cross section either, and where's my electronics side cutter???

*cough* almost forgot that my boss is again me in this case ::) At least I am happy that I have found a proper space for my hobby now :)
Title: Re: Guesses on what I am attempting here?
Post by: tautech on June 14, 2017, 03:54:41 PM
Run isolator for charging your electric scooter conversion.
Title: Re: Guesses on what I am attempting here?
Post by: tatus1969 on June 14, 2017, 04:51:17 PM
spoiler alert: the correct anwer was already given :clap:
Title: Re: Guesses on what I am attempting here?
Post by: CM800 on June 14, 2017, 07:19:57 PM
 At least share what silicon it is...

I stand by coilgun.

http://4hv.org/e107_plugins/forum/forum_viewtopic.php?147269 (http://4hv.org/e107_plugins/forum/forum_viewtopic.php?147269)
Title: Re: Guesses on what I am attempting here?
Post by: tatus1969 on June 14, 2017, 08:13:43 PM
At least share what silicon it is...

I stand by coilgun.

http://4hv.org/e107_plugins/forum/forum_viewtopic.php?147269 (http://4hv.org/e107_plugins/forum/forum_viewtopic.php?147269)
fair enough: https://www.digikey.de/product-detail/de/ixys/IXTN660N04T4/IXTN660N04T4-ND/6053919 (https://www.digikey.de/product-detail/de/ixys/IXTN660N04T4/IXTN660N04T4-ND/6053919) Anyway, more updates coming soon.
Title: Re: Guesses on what I am attempting here?
Post by: technix on June 14, 2017, 09:16:28 PM
At least share what silicon it is...

I stand by coilgun.

http://4hv.org/e107_plugins/forum/forum_viewtopic.php?147269 (http://4hv.org/e107_plugins/forum/forum_viewtopic.php?147269)
fair enough: https://www.digikey.de/product-detail/de/ixys/IXTN660N04T4/IXTN660N04T4-ND/6053919 (https://www.digikey.de/product-detail/de/ixys/IXTN660N04T4/IXTN660N04T4-ND/6053919) Anyway, more updates coming soon.
That is one SCARY MOSFET.
Title: Re: Guesses on what I am attempting here?
Post by: tatus1969 on June 14, 2017, 09:34:01 PM
I find it funny though that there is such a huge difference between SOT227 and SOT223 ^-^
Title: Re: Guesses on what I am attempting here?
Post by: P90 on June 14, 2017, 09:39:37 PM
i guess it's safe to say your planning on switching a big load on and off...
Title: Re: Guesses on what I am attempting here?
Post by: tatus1969 on June 14, 2017, 09:49:04 PM
more to add to the riddle: I need the die size, definitely need the Rdson, but don't need the power handling capability. And because it's only AWG8, to keep the wiring short.
Title: Re: Guesses on what I am attempting here?
Post by: tatus1969 on June 15, 2017, 07:22:43 AM
sorry, next update not until before Friday, I had a more urgent problem to solve as you have seen a few posts earlier. Mission accomplished :phew:

(http://www.eevblog.com/forum/projects/guesses-on-what-i-am-attempting-here/?action=dlattach;attach=324012)

DETAIL A
(http://www.eevblog.com/forum/projects/guesses-on-what-i-am-attempting-here/?action=dlattach;attach=324014)
Title: Re: Guesses on what I am attempting here?
Post by: blueskull on June 15, 2017, 08:08:26 AM
1. The answer has been given before #20.
2. It's not about the 2kW motor.
3. It's not a railgun (40V Vds_max).
4. You need low L/R as well as high die energy handling capacity, but don't care about continuous power dissipation.

I think my guess was correct.
Title: Re: Guesses on what I am attempting here?
Post by: DBecker on June 15, 2017, 08:51:50 AM
Given the lack of freewheel diode, it's unlikely to be powering anything even slightly inductive.  That rules out a motor controller, and points to a contact welder.  Or a fuse/breaker tester.

I expect the lack of snubber or capacitor at the device terminals will make this unreliable unless the turn-off time is quite slow, or the current decays on its own (e.g. it's a big capacitor, the easy way to build a single-shot battery terminal welder).

The main point of that $20 package is that it is isolated yet still has good heat transfer.  If you don't need the isolation, you can get the same die in a $4 TO247 and bolt it to a chunk of aluminum.  Although for a one-off you might decide the screw terminals are worth the extra money, especially if you buy a snubber module that mounts directly to the terminals.
Title: Re: Guesses on what I am attempting here?
Post by: blueskull on June 15, 2017, 09:02:42 AM
Given the lack of freewheel diode, it's unlikely to be powering anything even slightly inductive.  That rules out a motor controller, and points to a contact welder.  Or a fuse/breaker tester.

I expect the lack of snubber or capacitor at the device terminals will make this unreliable unless the turn-off time is quite slow, or the current decays on its own (e.g. it's a big capacitor, the easy way to build a single-shot battery terminal welder).

The main point of that $20 package is that it is isolated yet still has good heat transfer.  If you don't need the isolation, you can get the same die in a $4 TO247 and bolt it to a chunk of aluminum.  Although for a one-off you might decide the screw terminals are worth the extra money, especially if you buy a snubber module that mounts directly to the terminals.

These are MOSFETs, not BJTs. They are avalanche rated.
When BJT breaks down due to avalanche effect, highly concentrated carriers from emitter inject to base region and causes current multiplication, eventually triggering a secondary breakdown (RBSOA). That's why snubbers are mandatory for thyristors, BJTs and IGBTs.
When MOSFET breaks down, since it's a majority conductive device, there's no base region and current gain, hence no RBSOA. Since the drift region, source region and reverse doped channel region form a parasitic BJT, there is still a chance for secondary breakdown to happen in MOSFETs, but modern devices are designed to reduce hFE of this parasitic device, and for trench MOSFETs, this BJT is intrinsically very weak, compared with flat MOSFETs.
Title: Re: Guesses on what I am attempting here?
Post by: macona on June 15, 2017, 09:59:43 AM
Well, if you are building a capacitive discharge spot welder I would use a hockey puck SCR instead.
Title: Re: Guesses on what I am attempting here?
Post by: blueskull on June 15, 2017, 10:01:22 AM
Well, if you are building a capacitive discharge spot welder I would use a hockey puck SCR instead.

The T shaped RC battery connector tells me it's gonna be powered by an unprotected Li-ion pack (aka. RC battery).
Title: Re: Guesses on what I am attempting here?
Post by: LukeW on June 15, 2017, 11:02:05 AM
The little Deans connector looks really out of place on the giant wire.

Consider an Anderson connector, XT90 or a directly bolted connection onto battery terminals.
Title: Re: Guesses on what I am attempting here?
Post by: buck converter on June 15, 2017, 11:20:01 AM
high voltage Molotov cocktail. if that makes any sense
Title: Re: Guesses on what I am attempting here?
Post by: LukeW on June 15, 2017, 01:54:25 PM
So those beer bottles are supposed to be HV insulated standoffs?
Title: Re: Guesses on what I am attempting here?
Post by: tatus1969 on June 15, 2017, 03:50:47 PM
So those beer bottles are supposed to be HV insulated standoffs?
:-+ ;D

The T shaped RC battery connector tells me it's gonna be powered by an unprotected Li-ion pack (aka. RC battery).
They are okay for the same reason that I don't need a heatsink on the MOSFET.

Well, if you are building a capacitive discharge spot welder I would use a hockey puck SCR instead.
Compare the power dissipation of an SCR (at probably also higher price) with that of a MOSFET when switching high current, low voltage loads. Also, a capacitive discharge spot welder violates my requirement/assumption of this being a new idea.

the screw terminals are worth the extra money, especially if you buy a snubber module that mounts directly to the terminals.
That was exactly the rationale: how to attach AWG8 to TO247? Although it's a one-off - it it works well then I hope that it will not only be built by me.

I expect the lack of snubber or capacitor at the device terminals will make this unreliable unless the turn-off time is quite slow, or the current decays on its own (e.g. it's a big capacitor, the easy way to build a single-shot battery terminal welder).
An avalanche (or UIS, unclamped inductive switching) rated MOSFET can even be used to switch an inductor without any additional protection. They behave like zener diodes during breakdown (for a 40V device maybe at 50-60V), and just dissipate the stored magnetic energy. All you need to make sure is that their avalance energy rating is not exceeded, which is 5J for this one. This is because the energy is dumped into the die fast enough such that there is no heat transfer to the case. That is very useful for a flyback transformer for example, if it was not for EMC you could just remove the snubber network.
Title: Re: Guesses on what I am attempting here?
Post by: tatus1969 on June 17, 2017, 10:10:20 AM
@blueskull: razor sharp deduction  :-+

It's a bit late now, but I had to see it generating the first current pulse  :phew:

The scope screenshot shows the voltage across the AWG8 wire (35cm, approx 700 micro ohms). I couldn't believe it, but the peak does read 2.76V. That corresponds to 4kA  8)

I was a bit too scared for a full test by shorting the output leads, this one was taken with only a few litz strands twisted together. They vaporized in less than 100 microseconds... Which also means that I probably haven't seen yet what the circuit is capable of doing.

(http://www.eevblog.com/forum/projects/guesses-on-what-i-am-attempting-here/?action=dlattach;attach=324546)



Title: Re: Guesses on what I am attempting here?
Post by: Bendba on June 17, 2017, 10:25:04 AM
I thought lipo's internal resistance was in the order of 10 milli ohm. How do you get 4kA out of them?
Title: Re: Guesses on what I am attempting here?
Post by: blueskull on June 17, 2017, 10:33:23 AM
That's not 4ka. That's induced voltage. To accurately measure fast rising current, you need a current clamp or a high bandwidth coaxial current shunt.

I do a lot "few ka/us" measurements (my day time job is to design wide band gap power devices application and testers), and learned this the hard way. Sometimes even very small 1206 shunt can give you nasty inductive voltage.

The poor man's current shunt can be made out of a piece of coax cable, and short circuit inner and outer conductor on one end (current in), while on the other end, connect your scope between inner core and outer shielding. Current goes out from outer shielding.

What you get from scope is only resistive drop on outer shielding. Inductive voltage will be cancelled out by inner conductor.
Title: Re: Guesses on what I am attempting here?
Post by: tatus1969 on June 17, 2017, 06:05:44 PM
That's induced voltage.
That also immediately came into my mind, but I thought that the numbers would never add up for that - and skipped doing the math. But they do: Estimated loop inductance (low frequency, wires packed tightly) is 200nH. MOSFET switching time is 1.4us, so dI/dt would be 700A/us when assuming 1kA. That means, L*dI/dt = 140V. Now I would need to add skin effect calculations, but that is enough for me to close the case here.

high bandwidth coaxial current shunt
Thanks for that great trick!!

I thought lipo's internal resistance was in the order of 10 milli ohm. How do you get 4kA out of them?
That is valid for 18650 cells, but these are high current race LiPos rated at 40C discharge or 200A. Total circuit resistance should result in ~1kA. The second cursor in the screen shot is at 640mV, which corresponds to ~ 900A. That is good to know, because 4kA would just have been way more current than what I wanted to achieve.
Title: Re: low cost DIY battery spot welder [guesses on ... - solved]
Post by: tatus1969 on June 18, 2017, 11:47:33 PM
The control circuit is finished and works well after a few tweaks. A 555 timer generates 8V gate pulses from 1ms to 100ms. The current into a short is ~ 1kA (700mV across my "shunt").

So far so good, but after I slowly increased the pulse width, the transistor died. Its case didn't get hot at all, so I think that either the die or the bond wires must have given up.

I didn't expect that from the datasheet figures:
Id = 660A (chip capability)
Idm = 1800A (limited by maximum junction temp)
Il = 200A (external lead current limit)
Pd = 1040W
Rdson = 0.85mOhm

The power dissipation during the pulse should be ~850W, which the chip should be able to handle continuously. Am I right that the external lead current limit suggests that the bond wires probably failed?
Title: Re: low cost DIY battery spot welder [guesses on ... - solved]
Post by: tatus1969 on June 19, 2017, 01:55:58 AM
Ordered 4 x AUIRFSA8409-7P  FDB0105N407L for the same price as one of the broken one. Arranged in parallel they can handle 1840A continuous.

EDIT: updated to 6 parts in parallel. It is quite difficulty to find reliable information on package current limits. The AUIRFSA8409-7P datasheet mentions 360A (wire bond limited), which should mean that the bond wires will just not melt at this continuous current and theoretical package temp of 25°C. I hope to be on the safe side with 167A per chip, assuming reasonably well load sharing.
Title: Re: low cost DIY battery spot welder [guesses on ... - solved]
Post by: tatus1969 on June 22, 2017, 09:14:41 AM
OK, I decided to make things right this time. The FETs arrived, and their summed lead cross section exceeds that of the 300A ANL fuses that I also ordered. Lets hope that the cross section of all the bond wires is not too far from that. At least the fuses should be okay for a 1kA pulse of up to 0.5 secs.

The next problem was to find a way to connect the FETs to the AWG8 wiring. A PCB trace would certainly not be enough, and I don't want to spend money for PCBs with solid copper inlays.

The idea now is to use solid brass bus bars (8 x 12 mm) very close to the transistors, which will be able to carry the current, and hopefully also provide enough heat transfer to keep the solder from melting.

The first one is finished, that took again quite some time. But I started this, and I will succeed  :box:

(http://www.eevblog.com/forum/projects/guesses-on-what-i-am-attempting-here/?action=dlattach;attach=325828)

I also started designing a decent controller with the following specs:
- pulse energy control instead of time control, this will hopefully provide more consistent welds
- ANL / MEGA fuse holder
- 1kA switch for max 0.5sec
- 10 - 24V power supply is a separate unit, I will be using LiPos but capacitors could also be connected
- STM32 micro
- 1x8 LCD with backlight
- beeper
- input for foot pedal switch
- potentiometer for quick adjustment of pulse energy (I don't really like these 'modern' HMIs with push buttons)
- size approx 100 x 100mm
- most important: as low cost as possible, I estimate something around 50-70€

I would be happy to receive comments or feature requests. I want to make this available for everyone once it is stable, maybe run a small batch at Elecrow.

EDIT: circuit diagram outdated, see update here http://www.eevblog.com/forum/projects/guesses-on-what-i-am-attempting-here/msg1240839/#msg1240839 (http://www.eevblog.com/forum/projects/guesses-on-what-i-am-attempting-here/msg1240839/#msg1240839)
Title: Re: low cost DIY battery spot welder [guesses on ... - solved]
Post by: tatus1969 on June 24, 2017, 06:14:12 AM
The design is finished, boards and parts are ordered  :phew:
Title: Re: low cost DIY battery spot welder [guesses on ... - solved]
Post by: bktemp on June 24, 2017, 06:25:10 AM
The control circuit is finished and works well after a few tweaks. A 555 timer generates 8V gate pulses from 1ms to 100ms. The current into a short is ~ 1kA (700mV across my "shunt").

So far so good, but after I slowly increased the pulse width, the transistor died. Its case didn't get hot at all, so I think that either the die or the bond wires must have given up.
I can tell you why the mosfet failed:
Look at Fig. 2 on page 8 of the datasheet:
At 8V Vgs it can not supply more than 700-800A. Above that the voltage drop increases rapidly and also the losses. You simply exceeded the maximum power dissipation during the pulse.

If you use high current pulses, set the gate voltage as high as possible.
Title: Re: low cost DIY battery spot welder [guesses on ... - solved]
Post by: tatus1969 on June 24, 2017, 06:54:30 AM
I can tell you why the mosfet failed:
Look at Fig. 2 on page 8 of the datasheet:
At 8V Vgs it can not supply more than 700-800A. Above that the voltage drop increases rapidly and also the losses. You simply exceeded the maximum power dissipation during the pulse.

If you use high current pulses, set the gate voltage as high as possible.
You are absolutely right that this is the second mistake that I made. But as the lead current limit is also underrated, it remains open whether the leads or the die failed. As I don't have the required 15V available (12.6V Lipo), this MOSFET was the wrong choice anyway. And I have immediately checked, the new parts should run nicely down to 5.5V.  :phew:
Title: Re: low cost DIY battery spot welder [guesses on ... - solved]
Post by: MagicSmoker on June 24, 2017, 09:23:22 PM
Oops... too late now to implement one critical thing you omitted: a diode in between the LiPo battery and the PCB circuit with a decent amount of capacitance after the diode to provide "holdup" during the pulse firing.

The other suggestion is simply a matter of software: the best CD spot welders deliver two pulses of about 1-20ms width spaced about 1-20ms apart. The first pulse preheats and cleans the joint and the second pulse does the actual welding.

Title: Re: low cost DIY battery spot welder [guesses on ... - solved]
Post by: tatus1969 on June 24, 2017, 10:31:28 PM
Oops... too late now to implement one critical thing you omitted: a diode in between the LiPo battery and the PCB circuit with a decent amount of capacitance after the diode to provide "holdup" during the pulse firing.

The other suggestion is simply a matter of software: the best CD spot welders deliver two pulses of about 1-20ms width spaced about 1-20ms apart. The first pulse preheats and cleans the joint and the second pulse does the actual welding.
That makes it time to publish the finalized schematics  8) I also made provision for a freewheeling diode for the energy stored in the wiring inductance. But I expect that I don't need it. At 1kA, the stored magnetic energy is ~ 0.5 * L * I^2 = 0.5 * 200e-9 * 1000^2 = 0.1J. The MOSFETs should be able to handle this well, and they are repetitive avalance rated.

I plan to implement an energy based pulse control instead of a simple timer. i will try to see how that works with one single pulse, maybe that eliminates the need of a cleaning pulse. Constant energy delivered to the weld spot should result in more consistent welds. The circuit should also be able to detect a failed weld, in this case the requested energy cannot be delivered in a reasonable time.
Title: Re: low cost DIY battery spot welder [guesses on ... - solved]
Post by: tatus1969 on June 25, 2017, 12:53:38 AM
Assembled module...

(http://www.eevblog.com/forum/projects/guesses-on-what-i-am-attempting-here/?action=dlattach;attach=326647)

Title: Re: low cost DIY battery spot welder [guesses on ... - solved]
Post by: tatus1969 on July 02, 2017, 08:50:21 PM
Most software parts are prepared, the weld control loop already works with 10us cycle time and ADC conversions running with DMA. Really nice microcontroller architecture, you set up everything, and then it will continuously update an array in memory with conversion results.

While waiting for the boards to arrive next week I have machined electrode holders from 6x12x35mm brass. What do you think about it (these are not the final screws yet)?

Title: Re: low cost DIY battery spot welder [guesses on ... - solved]
Post by: tatus1969 on July 05, 2017, 08:07:00 AM
The boards have arrived earlier than expected. That allowed me to use the evening to solder and assemble one. So far everything seems to work! High current tests to follow.
Title: Re: low cost DIY battery spot welder [guesses on ... - solved]
Post by: mk_ on July 05, 2017, 04:54:52 PM


 The MOSFETs should be able to handle this well, and they are repetitive avalance rated.


Take care of the Gate-resistors... the 220 Ohm are fine for high powerlosses during switching, even if the FETs are avalanche-rated... you should reduce them down to something like 33 or 47 Ohm.
Also the 220 Ohm let each FET switch at a minimal different time - so one FET has to handle all aviable current (for a very short time)... lowering the Gateresistors results in better load-sharing @ switchingtimes...

Michael
Title: Re: low cost DIY battery spot welder [guesses on ... - solved]
Post by: tatus1969 on July 05, 2017, 08:35:58 PM


 The MOSFETs should be able to handle this well, and they are repetitive avalance rated.


Take care of the Gate-resistors... the 220 Ohm are fine for high powerlosses during switching, even if the FETs are avalanche-rated... you should reduce them down to something like 33 or 47 Ohm.
Also the 220 Ohm let each FET switch at a minimal different time - so one FET has to handle all aviable current (for a very short time)... lowering the Gateresistors results in better load-sharing @ switchingtimes...

Michael
thanks, I'll have to see how good my estimations are. I don't want to switch too fast to keep inductive ringing low, but fast enough to not exceed the max pulse energy. I expect anyway that the switching enwrgy is dissipated by one single transistor in worst case, when the gate threshold voltages differ. Switching time will be around 10us, at 1kA and 10V this would give a 0.1J ballpark figure. The MOSFETs are rated at 1.1J, so there should be plenty of room. Theoretically. But if I am wrong it will be a headache to change these resistors. ::)
Title: Re: low cost DIY battery spot welder [guesses on ... - solved]
Post by: tatus1969 on July 06, 2017, 07:27:20 PM
Yesterday I learned three things:
1) a multichanel ADC has a source for offset errors that I didn't realize before. When you look into my circuit diagram, you'll see that the MOSFET voltage measurement (OUT-) has a 10k filter resistance. According to the STM32's datasheet, that would be enough to settle to <1LSB at full speed. But I measured ~50mV at the ADC input, even with the MOSFETs shorted. Where did that come from? The ADC appnotes from ST didn't give a hint either. It took me half of the evening to figure out that this is charge injection from the previous conversion. The ADC configuration is to continuously convert all five available channels one after another. Therefore it has a MUX that connects one of the sources to the ADC input. That input has a capacitance. If, as in my case, the channel that precedes my problematic one has a siginifcantly higher voltage level, then the ADC input capacitor is charged to that level when switching to that channel. This dumps the stored from energy that capacitor out of the channel's GPIO, into the source network. As this is done repeatedly, this causes a constant current flow. The ADC input capacitance is 8pF, and the conversion rate is approx 100kHz. Assuming the adjacent channel sees 3.3V, and my problematic one has 0V, the current calculates to 100k * 0.5 * 3.3^2 * 8p = 4.3uA. The voltage drop on the 10k resistor then calculates to 43mV.  Gotcha!

2) a buck converter with bootstrapped power switch driver can never live with an output capacitor (in my case 2200uF) that 'survives' zero input power longer than the bootstrap capacitor. When the input voltage comes back, then there is nothing that can charge the bootstrap capacitor (as the output almost equals the input). This situation is only resolved when the output voltage has dropped far enough for a restart, unluckily leaving the supplied circuit dead during that time... Solution: move the freewheeling diode from the input to the output of the regulator. Luckily I can do that because I do not need a precise voltage.

3) the ADC inputs of the STM32 are not 5V tolerant. If I would have noticed that earlier, then I would not have to replace a dead microcontroller now. As I need a low leakage input protection, and a zener diode just doesn't deliver on that, I ordered some TL431. They will protect the OUT- input from high voltages.

Luckily the microcontroller did not die before allowing me to make this measurement. (Yellow: voltage across ~700uOhm of AWG8 wire, blue: voltage across MOSFETs) I don't believe the readings yet (why does blue approach zero??), but it suggests that the pulse current (here, into a 100% short circuit) is in the order of 1.5kA. Scary.

(http://www.eevblog.com/forum/projects/guesses-on-what-i-am-attempting-here/?action=dlattach;attach=329500)

Title: Re: low cost DIY battery spot welder [guesses on ... - solved]
Post by: tatus1969 on July 08, 2017, 04:52:27 AM
Interesting side note:

I have just finished completing the firmware code but cannot test it, because UPS didn't deliver the missing parts today as scheduled. This is the information that UPS gave me this morning:

(https://endless-sphere.com/forums/download/file.php?id=217997)

Something is wrong with this information - who can tell me first?

Hints:
a) it has been sunny and calm for a few days now
b) I live near Hamburg, Germany
Title: Re: low cost DIY battery spot welder [guesses on ... - solved]
Post by: tatus1969 on July 09, 2017, 08:21:34 AM
Yes! 8)

This is 0.1mm Hilumin.

A video showing the welder in action is in preparation!

(http://www.eevblog.com/forum/projects/guesses-on-what-i-am-attempting-here/?action=dlattach;attach=330408)
Title: Re: low cost DIY battery spot welder [guesses on ... - solved]
Post by: Fraser on July 09, 2017, 09:19:29 PM
Nice project :)

I bought a Chinese battery tag welder a few years ago and it has served me well. It uses a flipping great transformer And the double output pulse energy is controlled by a micro-controller. The only problem I have had with it is that on the higher current settings, it trips the nouse power breaker !

Your design looks very neat. Are you considering selling the PCB's or kits of parts ?

All the Best for the project completion.

Fraser
Title: Re: low cost DIY battery spot welder [guesses on ... - solved]
Post by: tatus1969 on July 10, 2017, 01:48:30 AM
Nice project :)
Thanks  :D It is performing extremely well. Even when doing a full pull (1kA for 200ms) the MOSFETs don't get even slightly warm. I am considering doing a test row by removing one after another to see how much I overdid it. I already decided to delete the brass bus bars for the bottom layer and replace them by washers and nuts. The only things that get warm are the electrodes, the battery connection (I knew that a Deans connector would be problematic) and, a bit sadly, the battery. But the design should also work with other power sources like capacitors or a lead acid battery, ...

it trips the nouse power breaker !
Energy efficiency is probably extremely low there. I found that welding 0.1mm Hilumin onto a 18650 cell requires 50 to 100 joules of energy. A 230V/10A wall outlet only needs 0.02 seconds to deliver that.

Are you considering selling the PCB's or kits of parts ?
Originally I wanted to make a one-off as you can see from my first pictures. But my solution has some unique features (apart from being very robust - I will explain those in the upcoming video), so I am planning to sell it in form of a kit. It depends on you makers and builders how that kit should look like. My idea is to only sell assembled/tested/programmed PCBs and the mechanical parts in raw form. This means (apart from things like bolts, nuts, cable lugs, ...) brass blocks cut to length, copper rod, and enough AWG8 wire. You would need to drill and cut the brass pieces, cut and form the copper rod into electrodes, and cut / crimp the cables. The other extreme would be supplying complete systems, but this involves considerable machining work and would make everything much more expensive. I need some feedback from you folks... And if someone is interested in a kit, just send me a PM.
Title: Re: low cost DIY battery spot welder [guesses on ... - solved]
Post by: Fraser on July 10, 2017, 03:52:55 AM
My feedback on this is that I would like the raw parts as I can do all the time consuming hardware bits that would cost a lot if it was a finished product. The raw kit would also encourage further hardware development in terms of probes, bus bars etc.

I am definitely interested in such a 'raw' kit. I will PM you.

Fraser
Title: Re: low cost DIY battery spot welder [guesses on ... - solved]
Post by: tatus1969 on July 10, 2017, 04:10:10 PM
The video is online!

If you like it, you can help me by sharing the video via Facebook etc.

https://youtu.be/Ceos88VO6p4
Title: Re: low cost DIY battery spot welder [guesses on ... - solved]
Post by: tatus1969 on July 11, 2017, 05:20:19 PM
I made a video where I am doing robustnes testing:

https://youtu.be/fWXphoDE_H8
Title: Re: low cost DIY battery spot welder [guesses on ... - solved]
Post by: maukka on July 11, 2017, 07:53:48 PM
That's an amazing project! Very well though out and I especially like the small form factor. Can't wait for the kit.
Title: Re: low cost DIY battery spot welder [guesses on ... - solved]
Post by: Kjelt on July 11, 2017, 09:44:20 PM
Originally I wanted to make a one-off as you can see from my first pictures. But my solution has some unique features (apart from being very robust - I will explain those in the upcoming video), so I am planning to sell it in form of a kit. It depends on you makers and builders how that kit should look like. My idea is to only sell assembled/tested/programmed PCBs and the mechanical parts in raw form. This means (apart from things like bolts, nuts, cable lugs, ...) brass blocks cut to length, copper rod, and enough AWG8 wire. You would need to drill and cut the brass pieces, cut and form the copper rod into electrodes, and cut / crimp the cables. The other extreme would be supplying complete systems, but this involves considerable machining work and would make everything much more expensive. I need some feedback from you folks... And if someone is interested in a kit, just send me a PM.

Great work there  :-+ For me the described kit without the machining would be great. Just a small description of the steps and taps and other tools involved would be enough.
Title: Re: low cost DIY battery spot welder [guesses on ... - solved]
Post by: Fraser on July 11, 2017, 10:29:16 PM
I am impressed with the performance of this excellent design. The control over the energy presented to the probe tips is excellent. As others have stated, commercial tag welders tend to use a double pulse system as that is said to improve welding performance by 'tacking' the metal together and then applying the true welding pulse to the joint. Your welder seems to cope fine as it is though.

As already stated, I would love the 'raw' kit to build. I think I would make probes that suit my specific needs.

One other comment, commercial tag welders tend to use cold drawn (hard) copper probes and these last well.

Fraser
Title: Re: low cost DIY battery spot welder [guesses on ... - solved]
Post by: tatus1969 on July 12, 2017, 02:56:21 AM
I will go ahead and make these items available:
1) PCB with all SMT components soldered and microcontroller programmed
2) set of through-hole components like capacitor, connectors, LCD, potentiometer, etc
3) fully assembled and programmed PCB
4) cable assembly for those who don't have a suitable crimp tool
5) set of mechanical components like bolts and nuts, excluding the parts that need machining
5a) the foot switch
6) set of raw brass and copper parts, cut to length
7) set of finished brass and copper parts
8 ) programmer for firmware updates that plugs into USB (the Segger tool is a full debugger and too costly), plus an update tool (Windows)
Title: Re: low cost DIY battery spot welder [guesses on ... - solved]
Post by: tatus1969 on July 12, 2017, 03:01:18 AM
I am impressed with the performance of this e cellent design.
Great work there  :-+
That's an amazing project! Very well though out and I especially like the small form factor.
Thanks  8)

The control over the energy presented to the probe tips is excellent. As others have stated, commercial tag welders tend to use a double pulse system as that is said to improve welding performance by 'tacking' the metal together and then applying the true welding pulse to the joint. Your welder seems to cope fine as it is though.
That could still be added easily, but I don't think that it is necessary because of my new approach. But I want to leave it up to the community to decide once the first kits are shipped.

One other comment, commercial tag welders tend to use cold drawn (hard) copper probes and these last well.
Thanks, noted!

Just a small description of the steps and taps and other tools involved would be enough.
for sure!
Title: Re: low cost DIY battery spot welder [guesses on ... - solved]
Post by: Fraser on July 12, 2017, 03:09:53 AM
Seeing your list of what will be made available in due course has me getting excited. Definitely something for everyone there.

Very much looking forward to further kit details and pricing when available. If I can afford it, I will be at the head of the queue for one :)

Many thanks again for shating your design.

Fraser
Title: Re: low cost DIY battery spot welder [guesses on ... - solved]
Post by: SvanGool on July 12, 2017, 05:10:33 AM
I am also interested in a kit.

I do think your circuit would also work for a (5 or 6x 2.7V or 1x14V) ultra-capacitor version, what do you think?
I still have less faith, then you do, of getting 1000 A out of a Li-Po that is rated for 250 A, on the long term.
Title: Re: low cost DIY battery spot welder [guesses on ... - solved]
Post by: tatus1969 on July 12, 2017, 05:46:35 AM
I am also interested in a kit.
I've put you on my list!

I do think your circuit would also work for a (5 or 6x 2.7V or 1x14V) ultra-capacitor version, what do you think?
The system will work well with any type of low impedance power source with a voltage range of 12V to ~35V. The weld algorithm continuously monitors output voltage and current, and by this it takes input voltage/current changes into account when calculating the accumulated weld energy. It also simplifies a CD welder because you don't need two capacitor banks for two-pulse welding. It still has to be confirmed by you guys, but I am confident that my system does not need a cleaning pulse.

For a capacitor based solution, you could also skip the fuse. I will add instructions on how to set it up without it. I added the fuse for pure safety reasons when using batteries. A shorted Lipo can quickly cause a fire.

As the impedance of the power source is a main contributor to the achieved current level, and the welder switch contributes only 140 micro-Ohms to that, you need to control the total loop resistance such that a desirable current is achieved. I did this by deliberately choosing "thin" AWG8 wires, which account for roughly 2mOhms. To help you controlling this, I added a current level readout after each shot (while keeping the trigger pressed), and the software immediately aborts when the current exceeds the switch limit of 2000A.

I still have less faith, then you do, of getting 1000 A out of a Li-Po that is rated for 250 A, on the long term.
For a good reason. The batteries definitely don't like how I treated them the last days, and I consequently keep them in an ammunition box when not in use. I think lead acid batteries are much more forgiving here, but I found the size and cost of these Lipos tempting. But I already think of paralleling four of them, because I don't want to have a car battery in my lab  8)
Title: Re: low cost DIY battery spot welder [guesses on ... - solved]
Post by: tatus1969 on July 12, 2017, 05:53:35 AM
Okay, I'll continue finishing the release design and send an RFQ to my PCB assembly company, but I wanted to share this one with you first. It's rather crazy (and educational?), please don't take it too seriously - I am a quality minded professional EE despite of what you see there  :o

https://youtu.be/JR3GJYScquc
Title: Re: low cost DIY battery spot welder [guesses on ... - solved]
Post by: Fraser on July 12, 2017, 06:25:24 AM
Tatus1969,

At last I have found a good use for the pile of brand new sealed Pb 12V 36Ah batteries that are sitting in my garage. I have looked after them for a couple of years hoping to find a use for them beyond jump starting my Mini Moke !  :-+

Fraser

Title: Re: low cost DIY battery spot welder [guesses on ... - solved]
Post by: casinada on July 12, 2017, 08:03:31 AM
 :-+
I'm tempted :)
Title: Re: low cost DIY battery spot welder [guesses on ... - solved]
Post by: SvanGool on July 12, 2017, 08:19:09 AM
For a capacitor based solution, you could also skip the fuse. I will add instructions on how to set it up without it. I added the fuse for pure safety reasons when using batteries. A shorted Lipo can quickly cause a fire.

Yes you could omit the fuse, but I wouldn't for the 6x 3000F/2.7V I have here, which is the equivalent of your Li-Po pack at 0.5 Ah (16.2V -> 12V) but capable of 1900 A (within spec), you still might get a fire :)
That's why I am interested to try the direction of a CD spotwelder with your circuit.
Title: Re: low cost DIY battery spot welder [guesses on ... - solved]
Post by: tatus1969 on July 13, 2017, 05:46:06 AM
For a capacitor based solution, you could also skip the fuse. I will add instructions on how to set it up without it. I added the fuse for pure safety reasons when using batteries. A shorted Lipo can quickly cause a fire.
For sure! But wouldn't the ESR of those not be a problem? The last time I worked with those it was still a few mOhm per cell.

Yes you could omit the fuse, but I wouldn't for the 6x 3000F/2.7V I have here, which is the equivalent of your Li-Po pack at 0.5 Ah (16.2V -> 12V) but capable of 1900 A (within spec), you still might get a fire :)
That's why I am interested to try the direction of a CD spotwelder with your circuit.
I've finished the redesign yesterday - I think that I didn't mention yet that I added an aux DC input that can be fed with 10~12V when the system is used as a CD welder. The problem here is that the internal holdup capacitor is only good for 250ms. The power caps will probably not be recharged quick enough to keep it from power cycling otherwise.

At last I have found a good use for the pile of brand new sealed Pb 12V 36Ah batteries that are sitting in my garage.
:-+
Title: Re: low cost DIY battery spot welder [guesses on ... - solved]
Post by: tatus1969 on July 13, 2017, 06:06:13 AM
There goes the next video, showing some improvements:
https://youtu.be/9-CQd02EDIs
Title: Re: low cost DIY battery spot welder [guesses on ... - solved]
Post by: Kjelt on July 13, 2017, 07:34:31 AM
It gets better and better, can't wait.  :-+
BTW I already have a Segger Jlink and STLink , probably many users here have one so can you make ordering the programmer for future fw updates optional ?
Title: Re: low cost DIY battery spot welder [guesses on ... - solved]
Post by: tatus1969 on July 13, 2017, 08:18:45 AM
can you make ordering the programmer for future fw updates optional ?
That's the plan!
Title: Re: low cost DIY battery spot welder [guesses on ... - solved]
Post by: Fraser on July 13, 2017, 08:32:49 AM
Having watched the videos of the probes in use, I think there is some room for improvement in that area as great care is needed to not touch the probes to each other. My Chinese transformer based welder uses approx 1.5mm hard drawn copper probes that are the required diameter for the contact surface with the tabs. To refinish the ends you just draw a file across them  :) Seem to work fine in my use.

Longer handles on the probes provides better directional control than you presently have over the probe placing. Your current probe design looks a bit like trying to write with a really short pencil.... its hard to control it well. In my experience you will likely get away with a sleeker and longer probe design. Maybe insulated brass bar around the same diameter as a ball point pen and grub screws holding the copper probe tips in place ?  Commercial systems I have seen use such an arrangement and there does not seem to be a problem with too high a resistance in the probes. My Chinese welder uses brass 'arms' to hold the probe tips in an arrangement similar to that which you have used. There are many possibilities as you know. With a lathe it is possible to create all manner of exotic probe designs including copper tips with a stepped offset for close parallel working  ;)

The joy of your design is that the builder of the unit may modify it to suit their needs and desires. You are still developing the design of the complete system so please do not take my comments as any form of criticism.

I will add some pictures of other probe designs in a minute

Best Wishes

Fraser
Title: Re: low cost DIY battery spot welder [guesses on ... - solved]
Post by: Fraser on July 13, 2017, 08:47:22 AM
Other probe designs, some good, some needing refinement !

Fraser

Links to original pages:

http://zeva.com.au/Projects/SpotWelder/ (http://zeva.com.au/Projects/SpotWelder/)
https://endless-sphere.com/forums/viewtopic.php?f=2&t=2633&start=400 (https://endless-sphere.com/forums/viewtopic.php?f=2&t=2633&start=400)
https://endless-sphere.com/forums/viewtopic.php?t=83411 (https://endless-sphere.com/forums/viewtopic.php?t=83411)
http://frikkieg.blogspot.co.uk/2010/01/ (http://frikkieg.blogspot.co.uk/2010/01/)

Title: Re: low cost DIY battery spot welder [guesses on ... - solved]
Post by: Kjelt on July 13, 2017, 11:53:52 PM
Having watched the videos of the probes in use, I think there is some room for improvement in that area as great care is needed to not touch the probes to each other.
Watch the latest video again, he already solved the issue in software  :)
Title: Re: low cost DIY battery spot welder [guesses on ... - solved]
Post by: tatus1969 on July 14, 2017, 12:16:03 AM
Having watched the videos of the probes in use, I think there is some room for improvement in that area as great care is needed to not touch the probes to each other.
Watch the latest video again, he already solved the issue in software  :)
I did what I can, but I think the automatic mode is still to be used with caution. That was maybe the "educational" part of my second last video. Having said that, this caution is advisable when using it in general, as you are dealing with power levels of 10kW+ here. And, if you decide to run it from Lipos (they don't really like this abuse), make sure to store them in a fire safe place. I have an old ammunition box for that.

But it's safe to say that nothing dangerous can happen from an accidental electrode short, apart from you getting a heart attack, and possibly damaged electrodes or battery tabs. The system has a hardware pulse duration limiter (250ms), and a fuse to prevent permanent short circuit current. I don't like the battery connection yet, that should definitely receive some heat shrink tubing as well. Imagine what happens when one of the bolts gets loose...
Title: Re: low cost DIY battery spot welder [guesses on ... - solved]
Post by: tatus1969 on July 14, 2017, 12:44:36 AM
@Fraser: thanks, that is very helpful. And I certainly don't take it as an offense. I am not quite happy with the electrode holders, there is way too much machining involved them and they are too bulky. It's just the resistance that is perfect, probably in the order of < 100uOhm. I think I will make some experiments with a coaxial design, a hard drawn copper rod, a brass tube, and grub screws.

I don't think that I will reduce the copper rod diameter, the robustness testing showed that they generate lots of heat. Although quite some of it will be transferred heat from the weld spot. But I think a minimum thermal mass is important.

I think I will change the tip shape to something like this:
Title: Re: low cost DIY battery spot welder [guesses on ... - solved]
Post by: SvanGool on July 14, 2017, 01:15:10 AM
I added an aux DC input that can be fed with 10~12V when the system is used as a CD welder. The problem here is that the internal holdup capacitor is only good for 250ms. The power caps will probably not be recharged quick enough to keep it from power cycling otherwise.

You have a max setting of 500 Joule (which is already huge). At 500F 15V (6x2.5V, to stay safe) the start capacity (CV2/2) is 56 kJ and the end capacity @12V is 36 kJ, so the budget is 20 kJ which is 40 pulses, before charging, that means that keeping your capacitor/microprocessor won't be a problem. This will be linearly less when the capacitors are smaller (besides that their internal resistance is normally higher also). The 3000F pack has a specced internal resistance of 1.74 mOhm and will probably need some larger gauge cable to come in the neighborhood of the energy-budget that you currently have.
Title: Re: low cost DIY battery spot welder [guesses on ... - solved]
Post by: Fraser on July 14, 2017, 05:11:05 AM
@Kjelt,

Many thanks. Sorry, I totally missed the significance of the change shown in the latest video. There is a warning sound plus delay before the welding voltage is presented to the probes. An excellent refinement for the auto mode :). I was concentrating on the additional data the display presents after the weld. Thanks again for getting me to re-watch the video.

Fraser
Title: Re: low cost DIY battery spot welder [guesses on ... - solved]
Post by: tatus1969 on July 14, 2017, 05:14:14 AM
You have a max setting of 500 Joule (which is already huge). At 500F 15V (6x2.5V, to stay safe) the start capacity (CV2/2) is 56 kJ and the end capacity @12V is 36 kJ, so the budget is 20 kJ which is 40 pulses, before charging, that means that keeping your capacitor/microprocessor won't be a problem. This will be linearly less when the capacitors are smaller (besides that their internal resistance is normally higher also). The 3000F pack has a specced internal resistance of 1.74 mOhm and will probably need some larger gauge cable to come in the neighborhood of the energy-budget that you currently have.
I think that you have a mistake in your calculations (or maybe I misunderstood something). When you put six capacitors of 500F/2.5V each into series, then this makes an 83.3F / 15V capacitor. When going 15V -> 5V, it can deliver 8333J. Which is still more than enough, and you still don't need the aux DC input. Anyway, that's only 50ct extra  ;)

Edit: I think I got it: you are using 6x BCAP0650 PBCAP3000 270 K04 in series. That means that you will need to add something that limits current to an acceptable level. At (1.74 + 0.14) mOhm, the starting current would be way above the 2kA limit of my welder. Hence to use larger gauge and maybe longer probe leads.
Title: Re: low cost DIY battery spot welder [guesses on ... - solved]
Post by: SvanGool on July 14, 2017, 09:50:58 AM
Sorry, I was not clear: I am talking about 6x3000F/2.7V (Maxwell BCAP3000 P270 K04, see also here (http://www.eevblog.com/forum/projects/guesses-on-what-i-am-attempting-here/msg1253998/#msg1253998)) in series. Which makes a 500F/16.2V capacitor pack (if charged to the edge, I prefer 6x2.5V=15V).

You are correct, if the max starting current is 2 kA (the advised max is 1.9 kA for the BCAP3000) and the cap pack resistance = minim. 1.74 mOhm (6 x 0.29) then at least 6.2 mOhm is needed for cabling and tips. The advantage is, that your pulse length for a 200 J pulse would only need to be app. 7 mS and everything would be within the spec of the capacitors (no ammunition box needed anymore).
 

Title: Re: low cost DIY battery spot welder [guesses on ... - solved]
Post by: Kjelt on July 14, 2017, 06:05:07 PM
But you need a mortgage on the house to buy these supercaps  ;D  I looked them up on Farnell and they are €200 each  :scared:
Very nice though if you find them in a dumpster.
Title: Re: low cost DIY battery spot welder [guesses on ... - solved]
Post by: SvanGool on July 14, 2017, 07:30:39 PM
The price at Farnell is, for this case, not very representative  :)

If you follow the ebay-like sites for a period, you can find 6 Maxwell new/used caps in the range of 650F-3400F for a price much lower than the single Farnell price, but do watch out for "shady" sellers.
I'm trying to establish with tatus1969 what the lowest workable capacitor type would be, but we first need to have our "math" correct.
At the end, it is also preferable to have balancing or over-voltage protection for the caps.
Title: Re: low cost DIY battery spot welder [guesses on ... - solved]
Post by: tatus1969 on July 14, 2017, 10:23:07 PM
16.2V capacitor pack (if charged to the edge, I prefer 6x2.5V=15V).
I've implemented a 5.8F/140V pack in the past, and we had the manufacturer in house for technical discussions. They stated that, in order to maintain their lifetime, you do not need to derate voltage, and it is much more important to keep the cell temperatures as low as possible. It's like for any other electrolytic capacitor: every 10°C less doubles the lifetime.

cap pack resistance = minim. 1.74 mOhm (6 x 0.29)
Be careful, the datasheet states this as the maximum initial ESR. There will certainly be some spread to lower values, so you need some headroom. The software based overcurrent detection will immediately trip at >= 2kA, and the measurement accuracy is not very high. It depends on production spread of the MOSFETs, the gate drive voltage (which is decreasing during the pulse), and the brass bus bar construction repeatability. Things like mounting torque...

I'm trying to establish with tatus1969 what the lowest workable capacitor type would be, but we first need to have our "math" correct.
At the moment I am busy building up price structure and stock, but I've already set one of the next tasks to investigate this: how should a power capacitor look like that
- delivers enough energy to the load in a short enough time
- stays within given voltage limits during this
- has the lowest possible price to achieve the above

It is not only a matter of ESR, you need to juggle between that and the voltage span. At higher voltages, you can allow more ESR.

Some numbers are already there for my welder:
- max input voltage: 30 V
- min input voltage for welding: 12 V
- min input voltage to keep microcontroller from power cycling: 4 V
- resistance of power switch, cabling and electrodes: approx 2.5 mOhm (can be reduced to <<1mOhm by using more material)
- resistance of weld spot: approx 1 - 4 mOhm

At the end, it is also preferable to have balancing or over-voltage protection for the caps.
As we don't need to be energy efficient, I am thinking of a passive solution with beefy equalization resistors. Their current must exceed the maximum required equalization current, and can be calculated from capacitance spread and leakage current. Of course that doesn't work as overvoltage protection.
Title: Re: low cost DIY battery spot welder [guesses on ... - solved]
Post by: tatus1969 on July 15, 2017, 02:44:34 AM
A first lot of 25 PCBs is ordered, and I have the system part list and pricing complete. I will add articles to my web shop today, stay tuned!

And I have changed the electrode design like this now. The cable will be soldered to the electrode holder. The tip will be held into place with one screw/nut. The (brass) nut will be soldered to the tube to ease electrode replacement.

Please tell me what you think about it? The construction is much simpler now and can be machined quicker.
Title: Re: low cost DIY battery spot welder [guesses on ... - solved]
Post by: Fraser on July 15, 2017, 03:05:10 AM
Nice new probe design :)

Looking forward to being able to purchase this unit.

Fraser
Title: Re: low cost DIY battery spot welder [guesses on ... - solved]
Post by: Kjelt on July 15, 2017, 08:03:48 AM
The cable will be soldered to the electrode holder.
Please tell me what you think about it? The construction is much simpler now and can be machined quicker.
I do like the new tip connection. The cable to holder I am not so sure.
I am no mechanical expert so could be wrong but thinking out loud, a soldered connection should be inferior to a well crimped connection where the metals will become one without much of a transition resistance. Esp. with huge currents like in this application I would choose a direct crimp connection or hard welding connection.
Title: Re: low cost DIY battery spot welder [guesses on ... - solved]
Post by: tatus1969 on July 15, 2017, 08:45:28 AM
The cable will be soldered to the electrode holder.
Please tell me what you think about it? The construction is much simpler now and can be machined quicker.
I do like the new tip connection. The cable to holder I am not so sure.
I am no mechanical expert so could be wrong but thinking out loud, a soldered connection should be inferior to a well crimped connection where the metals will become one without much of a transition resistance. Esp. with huge currents like in this application I would choose a direct crimp connection or hard welding connection.
Good point. I ordered parts to make a build and see how it performs. The soldering will be done with solid solder / flux / blow torch, in order to achieve a good fill. I always have in mind that everybody should be able to do the machining/assembly work, and not everybody has a suitable crimp tool that can handle 6mm diameter. Me neither... I mainly want to see kit parts.
Title: Re: low cost DIY battery spot welder [guesses on ... - solved]
Post by: Fraser on July 15, 2017, 08:49:39 AM
I see the main module is now in your shop. Are you taking pre-orders ?
If so, I would like to pre-order a unit plus some of the cables with pre-crimped ends.

Fraser
Title: Re: low cost DIY battery spot welder [guesses on ... - solved]
Post by: tatus1969 on July 15, 2017, 09:12:38 AM
Just a quick update: the first items are online on https://www.kicksurfer.de/index.php/shop/ (https://www.kicksurfer.de/index.php/shop/)
I will add more tomorrow, as it is late here.

The first batch of electronic sets is ordered and I estimate that I can add them to the stock by mid August. It will not be possible to place an order for that before, but as I appreciate your help here I want to respect the order in that you registered interest. If you want to buy an electronics set, then please register as a customer on my site and give me a PM here that you actuall plan to purchase an electronics set. I will reserve one set for you for the duration of one week after stock arrival.

All the other items will not be that problematic, as I can source them quickly. However, I will not build up a large stock of them because I think that most of you will want to source as much as possible locally and do the machining/soldering/crimping/assembling work by yourself.
Title: Re: low cost DIY battery spot welder [guesses on ... - solved]
Post by: tatus1969 on July 15, 2017, 09:14:09 AM
I see the main module is now in your shop. Are you taking pre-orders ?
If so, I would like to pre-order a unit plus some of the cables with pre-crimped ends.

Fraser
You are quicker than I can type  ;)
My shop system (Wordpress+Woocommerce) unfortuately does not support pre orders  :-//
Title: Re: low cost DIY battery spot welder [guesses on ... - solved]
Post by: Fraser on July 15, 2017, 09:21:39 AM
Reservation request PM sent. I am a committed customer of your kit  :)   :-+

Fraser
Title: Re: low cost DIY battery spot welder [guesses on ... - solved]
Post by: tatus1969 on July 16, 2017, 02:05:48 AM
Quote from: tatus1969
It will not be possible to place an order for that before
I'll have to take that back, I just wasn't familiar enough with that system.

Sorry for the confusion!!!

WOW, that's an endless world of possibilities there! If someone needs a guide to setting up a Wordpress + Woocommerce server, here is another expert   ;)

Okay, no more products added there yet, but I managed to set up the full chain for the electronics module, including
- accepting pre-orders now - I'll serve them in the order that they come in
- the option whether you want me to complete it (solder LCD and dial pot), or you want to do that
- world wide automatic shipping rate calculator
- safe credit card payment via stripe

I'll add Paypal as well, but my business account there needs verification and they told me that this would take 2-3 weeks  :shock:

I've set the limit to 20 copies now, to accomodate the possibility that not all of the 25 ordered are good.

Please order only one per person for now, in order to allow others receiving one. I need to refuse larger orders for the first batch. No problem of course later, after successful ramp up!

If you plan to purchase other options that are not in the store yet, please wait and you'll be offered a combined shipping rate. So you don't need to pay shipping twice.

I've activated the website again and do accept orders  8)
Title: Re: low cost DIY battery spot welder [guesses on ... - solved]
Post by: Fraser on July 16, 2017, 02:49:27 AM
I just went to pre-order. The price has gone up from 89 Euro to 99 Euro.

Is this correct please ?

Fraser
Title: Re: low cost DIY battery spot welder [guesses on ... - solved]
Post by: tatus1969 on July 16, 2017, 02:54:53 AM
I just went to pre-order. The price has gone up from 89 Euro to 99 Euro.

Is this correct please ?

Fraser
No, I separated it differently before. It was
- 89€ for the partially soldered board
- 10€ for the additional components LCD / dial pot / pin header / knob

Now it is everything included in one package. I thought that it didn't make much sense to sell these separately. I initially did that because, if you want to design a housing for it, then you will want to use a different potentiometer type. This one does not have a mounting thread. But that part is worth less than 1€, so I canceled that now.
Title: Re: low cost DIY battery spot welder [guesses on ... - solved]
Post by: Fraser on July 16, 2017, 03:15:18 AM
 No worries :)

I see from your letter you will be adding additional items. I have one controller board in my basket. I will add to that later.

Best Wishes

Fraser
Title: Re: low cost DIY battery spot welder [guesses on ... - solved]
Post by: tatus1969 on July 16, 2017, 07:06:25 AM
The remaining items are online as well. As I will be doing all the soldering, machining, and assembly work by myself for the time being, I need to set the prices for that relatively high. When this product is ramping up nicely, then this may change in the future.
Title: Re: low cost DIY battery spot welder [guesses on ... - solved]
Post by: Fraser on July 16, 2017, 07:49:12 AM
I have just placed my pre-order. I went for the partially unassembled PCB, two 300A fuses (one and a spare) plus the raw bus bars. The rest I can sort out for myself.

This design is exactly what I have been searching for :) Perfect !
I know the parts for the PCB were not cheap so thanks for the hobby friendly pricing.

There was mention of a programmer for updating the firmware on the unit. Some details of the required programmer would be appreciated.

Best Wishes from the UK

Fraser
Title: Re: low cost DIY battery spot welder [guesses on ... - solved]
Post by: Kjelt on July 16, 2017, 08:27:04 AM
I'll order tomorrow, have to figure out what to get, are those high current connectors shown in any video already?
Title: Re: low cost DIY battery spot welder [guesses on ... - solved]
Post by: tatus1969 on July 16, 2017, 08:35:16 AM
I have just placed my pre-order. I went for the partially unassembled PCB, two 300A fuses (one and a spare) plus the raw bus bars. The rest I can sort out for myself.
Got it! Thanks!

I know the parts for the PCB were not cheap so thanks for the hobby friendly pricing.
Yes, especially the MOSFETs. But I decided pro robustness and to accept a higher price for that. Also the microcontroller had to be a bit beefier because it has to do the entire energy calculation algorithm and all safety measures in a 10µs cycle.

There was mention of a programmer for updating the firmware on the unit. Some details of the required programmer would be appreciated.
It's very simple, a FTDI RS232 adapter and a cable. The red socket on the welder is a combined UART / JTAG interface. The firmware will run a dedicated in-application-programming code. I cannot show this part yet because it is not ready yet. That will take some more days to implement, the framework and the theoretical design is finished.
Title: Re: low cost DIY battery spot welder [guesses on ... - solved]
Post by: Fraser on July 16, 2017, 08:43:18 AM
Wonderful news on the programmer. Thank you for keeping it simple. I have lots of FTDI RS232 converters  :)

I shall start planning my version of the probes, case and power source. I have plenty of time to source the required parts.

Best Wishes

Fraser
Title: Re: low cost DIY battery spot welder [guesses on ... - solved]
Post by: tatus1969 on July 16, 2017, 09:02:40 AM
Wonderful news on the programmer. Thank you for keeping it simple. I have lots of FTDI RS232 converters  :)
You need one without level shifter that uses 3.3V TTL levels. The pinout of the red connector is here in the thread:

http://www.eevblog.com/forum/projects/guesses-on-what-i-am-attempting-here/msg1240839/#msg1240839 (http://www.eevblog.com/forum/projects/guesses-on-what-i-am-attempting-here/msg1240839/#msg1240839)

Not to forget: the schematic there is not up to date anymore, nor is it working like that 8)
Title: Re: low cost DIY battery spot welder [guesses on ... - solved]
Post by: Fraser on July 16, 2017, 09:46:35 AM
Many thanks. I have 3V3 types as well as 5V so all sorted on that front :)
Will the documentation that comes with the unit contain a schematic and brief theory of operation please ?

Best Wishes

Fraser
Title: Re: low cost DIY battery spot welder [guesses on ... - solved]
Post by: Fraser on July 16, 2017, 08:28:13 PM
I have now ordered the following via eBay:

1m Red 8AWG Turnigy Silicone coated cable
1m Black 8AWG Turnigy Silicone coated cable
Ten 100mm Brass tubes - 6mm with 1mm wall
300mm x 4mm copper rod
Ten high quality solder/crimp lugs. 10mm2 / 6mm

I wanted more parts than are actually needed to enable me to experiment a little. The cost mounts up though. The kits offered by the OP are very good value and recommended for most users of the unit.

With regard to terminating the cables with the large lugs. There are two options open to me, Soldering or Crimping. Crimping can be a reliable connection, but only if a quality crimp is made. This normally requires an expensive high quality crimper. The crimp needs to be sit tight to avoid oxidation issues. Where such a high quality crimp is not possible, soldering is the preferred method, even in high current applications. The solder fills the voids and provides an excellent connection to all cable strands. The down side of soldering is that the solder can travel down the cable making the area adjacent to the connector stiff. I am going to so,dear mine with my high powered soldering iron.

Fraser
Title: Re: low cost DIY battery spot welder [guesses on ... - solved]
Post by: TheAmmoniacal on July 16, 2017, 10:03:51 PM
Great little device you've made  :-+

I'm just curious, would it help to use flux? Common solder one or plumber type? Sure it will just burn into smoke rapidly, but will the surface finish/oxidation, and color look better? Any difference in the quality of the weld?
Title: Re: low cost DIY battery spot welder [guesses on ... - solved]
Post by: tatus1969 on July 16, 2017, 10:33:15 PM
Will the documentation that comes with the unit contain a schematic and brief theory of operation please ?
Noted, I'll include that.

This normally requires an expensive high quality crimper.
I've ordered one of these, they are not as expensive as you might think. They develop huge force and should make reliable, gas-tight crimps.

(https://images-na.ssl-images-amazon.com/images/I/515OV5VQ9ML._SY355_.jpg)

Great little device you've made  :-+

I'm just curious, would it help to use flux? Common solder one or plumber type? Sure it will just burn into smoke rapidly, but will the surface finish/oxidation, and color look better? Any difference in the quality of the weld?
Thanks  :)
Its welding not soldering, the temperatures are way higher here, maybe 1000degC. I think that flux will just vaporize or burn.

The welds actually look better than many of those which I showed in the videos. That was letting you participate in me experimenting, and of course to discover the limits. A typical weld of 0.1mm nickel strip to an 18650 cell typically does not produce any coloring.

I just made these welds on a dead battery to show how a regular weld looks like: this is 0.2mm 0.1mm nickel strip, the energy is set to 30J. It can probably still be lowered.

(http://www.eevblog.com/forum/projects/guesses-on-what-i-am-attempting-here/?action=dlattach;attach=332388)

EDIT2: Okay, I'll have to take back everything that I said about using flux. The below welds are with 0.2mm nickel strips, and you can see the coloring which cannot be prevented when doing it as usual. Except both leftmost welds per cell, where I added a drop of flux! Awesome, I can definitely recommend that to everyone! The used flux was Chipquik SMD291.

(http://www.eevblog.com/forum/projects/guesses-on-what-i-am-attempting-here/?action=dlattach;attach=332390)

Title: Re: low cost DIY battery spot welder [guesses on ... - solved]
Post by: TheAmmoniacal on July 16, 2017, 10:36:26 PM
Those welds do look great, no improvement needed! Maybe try a few with flux for fun? :)
Title: Re: low cost DIY battery spot welder [guesses on ... - solved]
Post by: tautech on July 16, 2017, 10:48:10 PM
Those welds do look great, no improvement needed! Maybe try a few with flux for fun? :)
I don't see any point, if you watch the vid there's an attempt to tear the spot welded strip off and to apply additional force than what was shown would only tear the strip or the battery.
This IMO gives the same result as professionally welded battery packs and you never see flux on them.
Title: Re: low cost DIY battery spot welder [guesses on ... - solved]
Post by: tatus1969 on July 16, 2017, 10:55:11 PM
Those welds do look great, no improvement needed! Maybe try a few with flux for fun? :)
did that, updated my previous post  ;)
Title: Re: low cost DIY battery spot welder [guesses on ... - solved]
Post by: Fraser on July 17, 2017, 12:34:27 AM
Regarding cell surface condition.......

OEM's would reject any cell that showed oxidisation or corrosion on the welding surfaces. I have bought many new Ni-Mh cells at discounted prices because they have suffered some level of corrosion on the end caps. Such cells are easily 'recovered' by cleaning the surfaces before spit welding. An OEM does not want such hassle and does not use flux as a result.

Cleaning of cell end caps is a good idea, especially if they have been sitting around for a while. Oxide layers do effect the way the weld forms as they have to be burnt off. This MAY be the true reason behind the double pulse protocol used by some battery tab welders.

I so no problem with using electronics rated flux when welding, it burns odd and cleans the surfaces in the process.

One matter that needs consideration when welding cells is heat. If too much heat is present on the cells surface, damage can result. This is especially so with button cells. Plastic seals can melt or boiling of the cells electrolyte can result.  The minimum weld current and duration should be used in such cases to avoid cell damage. The thin nickel tabs can be discoloured by the very high temperatures and I would be a bit careful about seeing that if working with fragile cell constructions, such as button cells. When using my Chinese Tab welder the cells surface does not get too hot to touch and the tag rips before the weld breaks. There is no discolouration around the welds but they are a lot smaller diameter ! I do prefer the welds produced by this DIY version. Far more in keeping with those I have seen on commercial batteries.

Fraser
Title: Re: low cost DIY battery spot welder [guesses on ... - solved]
Post by: tatus1969 on July 17, 2017, 06:10:22 AM
hmmmm. Fraser that's very interesting, but I'm not sure if you have understood me correctly. I haven't added flux between battery and tab, but between tab and electrode.
Title: Re: low cost DIY battery spot welder [guesses on ... - solved]
Post by: Fraser on July 17, 2017, 06:21:10 AM
Ooooh, I had not thought of that. Interesting.

Fraser
Title: Re: low cost DIY battery spot welder [guesses on ... - solved]
Post by: Kjelt on July 17, 2017, 06:50:38 AM
Also placed my pre-order (see your pm)  :-+ .
Just wondering where do you order those metal strips that you use for the batterypack assembly ? Link ?

Title: Re: low cost DIY battery spot welder [guesses on ... - solved]
Post by: tatus1969 on July 17, 2017, 08:03:17 AM
Also placed my pre-order (see your pm)  :-+ .
Just wondering where do you order those metal strips that you use for the batterypack assembly ? Link ?
I got them from ebay, the search term is Hilumin strip, or battery spot welding nickel strip. For example http://www.ebay.de/itm/2m-Solid-Pure-Nickel-Strap-Strip-Spot-Welding-battery-12mm-x-0-15mm-12x0-15-40A-/263057602801 (http://www.ebay.de/itm/2m-Solid-Pure-Nickel-Strap-Strip-Spot-Welding-battery-12mm-x-0-15mm-12x0-15-40A-/263057602801)
Title: Re: low cost DIY battery spot welder [guesses on ... - solved]
Post by: Fraser on July 17, 2017, 08:16:10 AM
I have several types of strip that I bought from eBay. Some are described as pure nickel whilst others are nickel plated steel. I am uncertain whether the nickel plated steel is any good as I have yet to use it. I do know that it is important that the strip is not TOO conductive as that can present a very low tab resistance path to the probes. This may reduce current flow into the battery cap, and may result in a lower quality weld. That is why you do not see copper battery tabs on welded batteries.

Fraser
Title: Re: low cost DIY battery spot welder [guesses on ... - solved]
Post by: tatus1969 on July 17, 2017, 08:58:14 AM
I forgot to mention, I recently tested these ones:

http://www.ebay.de/itm/10-St%C3%BCck-Hochstrom-L%C3%B6tfahnen-L%C3%B6tbr%C3%BCcken-Akkuverbinder-zb-f%C3%BCr-18650-27x9x0-3/162191637024?ssPageName=STRK%3AMEBIDX%3AIT&_trksid=p2057872.m2749.l2649 (http://www.ebay.de/itm/10-St%C3%BCck-Hochstrom-L%C3%B6tfahnen-L%C3%B6tbr%C3%BCcken-Akkuverbinder-zb-f%C3%BCr-18650-27x9x0-3/162191637024?ssPageName=STRK%3AMEBIDX%3AIT&_trksid=p2057872.m2749.l2649)

Their advantage is that they are 0.3mm and can carry higher battery currents, and they can yet be welded with low energies because of their pre-shaped spots. Just make sure not to repeat my silly mistake and always probe pairs of contacts with the slit inbetween.
Title: Re: low cost DIY battery spot welder [guesses on ... - solved]
Post by: Fraser on July 17, 2017, 09:01:35 AM
 This article caught my eye. How to check what strip material you have been sold ...... pure nickel or the cheaper plated steel.

http://www.ebikeschool.com/how-to-differ-between-pure-nickel-strip-battery-tabs-vs-steel-core/ (http://www.ebikeschool.com/how-to-differ-between-pure-nickel-strip-battery-tabs-vs-steel-core/)

It looks like for my battery applications, steel tabs will be fine. I am not working at high currents where small resistive losses become a factor.

Fraser
Title: Re: low cost DIY battery spot welder [guesses on ... - solved]
Post by: Fraser on July 17, 2017, 09:08:40 AM
A crude but still interesting test of battery connection strip.......

http://www.electric-skateboard.builders/t/carbon-steel-strip-vs-stainless-steel-strip-vs-pure-nickel-strip-fake-nickel-strips-tested-practical-performance-test-results/18633 (http://www.electric-skateboard.builders/t/carbon-steel-strip-vs-stainless-steel-strip-vs-pure-nickel-strip-fake-nickel-strips-tested-practical-performance-test-results/18633)

Fraser
Title: Re: low cost DIY battery spot welder [guesses on ... - solved]
Post by: tautech on July 17, 2017, 05:32:47 PM
hmmmm. Fraser that's very interesting, but I'm not sure if you have understood me correctly. I haven't added flux between battery and tab, but between tab and electrode.
What was your rationale for doing this ?  :-//
Title: Re: low cost DIY battery spot welder [guesses on ... - solved]
Post by: tatus1969 on July 17, 2017, 06:22:53 PM
What was your rationale for doing this ?  :-//
curiosity. to see if that helps reducing coloring. it does 8)

This article caught my eye. How to check what strip material you have been sold ...... pure nickel or the cheaper plated steel.

http://www.ebikeschool.com/how-to-differ-between-pure-nickel-strip-battery-tabs-vs-steel-core/ (http://www.ebikeschool.com/how-to-differ-between-pure-nickel-strip-battery-tabs-vs-steel-core/)
I can make another proposal: measure up a reasonable length of your strip material, press the electrodes of my welder against the ends of that, trigger a pulse of lets say 50J, and take the ohmic resistance that it reports to determine the material  ;)
Title: Re: low cost DIY battery spot welder [guesses on ... - solved]
Post by: tautech on July 17, 2017, 07:07:07 PM
What was your rationale for doing this ?  :-//
curiosity. to see if that helps reducing coloring. it does 8)
In my mind it's just acting as a coolant then so other liquids could have the same result........could you try some others to further satisfy curiosity ?
Title: Re: low cost DIY battery spot welder [guesses on ... - solved]
Post by: tatus1969 on July 18, 2017, 12:16:12 AM
What was your rationale for doing this ?  :-//
curiosity. to see if that helps reducing coloring. it does 8)
In my mind it's just acting as a coolant then so other liquids could have the same result........could you try some others to further satisfy curiosity ?
I'm a bit hesitant to use other liquids like water, because I am afraid of eruptive vaporization. It is just that advantage which flux has that it just crumples instead.
Title: Re: low cost DIY battery spot welder [guesses on ... - solved]
Post by: negativ3 on July 18, 2017, 01:42:22 AM
Please let us know when Paypal is ready to use.
Title: Re: low cost DIY battery spot welder [guesses on ... - solved]
Post by: tatus1969 on July 18, 2017, 01:45:01 AM
Please let us know when Paypal is ready to use.
I had them on the phone last Saturday, they told me that unlocking it for businesses is a manual process and that I will have to wait for one to two weeks  |O I will definitely keep you updated, and notify you immediately.
Title: Re: kWeld - "Next level" DIY battery spot welder
Post by: Kjelt on July 18, 2017, 04:31:26 AM
Oops did we have to wait with the pre-order? I am confused  :-//
Title: Re: kWeld - "Next level" DIY battery spot welder
Post by: Fraser on July 18, 2017, 04:57:25 AM
From what I understand,

Pre order is fine if you do not mind using the 'Stripe' secure credit card payment system. The delay relates to Frank getting his PayPal approved for accepting payments via the web page.

Fraser
Title: Re: kWeld - "Next level" DIY battery spot welder
Post by: Kjelt on July 18, 2017, 05:05:52 AM
Ok good to hear  :-+ , problem is more that credit card transactions cost the seller more than a paypal transfer.
Title: Re: kWeld - "Next level" DIY battery spot welder
Post by: tatus1969 on July 18, 2017, 06:18:53 AM
From what I understand,

Pre order is fine if you do not mind using the 'Stripe' secure credit card payment system. The delay relates to Frank getting his PayPal approved for accepting payments via the web page.

Fraser
Thanks for answering this for me  :)

Ok good to hear  :-+ , problem is more that credit card transactions cost the seller more than a paypal transfer.
That appears not to be the case here. Paypal charges more than Stripe... Anyway, they both charge something, but that is my duty  ;)
Title: Re: kWeld - "Next level" DIY battery spot welder
Post by: Kjelt on July 18, 2017, 06:50:23 AM
Good to hear now I don't feel guilty  :)
Title: Re: kWeld - "Next level" DIY battery spot welder
Post by: tatus1969 on July 18, 2017, 06:54:41 AM
Good to hear now I don't feel guilty  :)
Companies like Visa and Paypal should feel guilty, not you!
Title: Re: kWeld - "Next level" DIY battery spot welder
Post by: tatus1969 on July 18, 2017, 06:57:18 AM
It was again exaggerated complexity that kept me from getting where I want. There is Paypal, Paypal Express, Paypal PLUS, then they tell you something about different APIs, bank account authorization, and so on. To summarize this: Paypal is now available in the shop, it was again easier/quicker than expected!
Title: Re: kWeld - "Next level" DIY battery spot welder
Post by: tatus1969 on July 18, 2017, 07:33:06 AM
I wasn't happy with the lifetime of my regular Turnigy 3S/5Ah/50C packs. I know that my usage profile for welding with them was far from daily life duty, I think during my abuse test with the cookie can it was more or less 50% duty cycle at 1kA. I have ruined two packs until they both showed noticable swell. They are still usable, and pulse current is still at 900A, but I am aware that this literally playing with fire, and I wouldn't copying this to anyone.

Hence, I decided to order one of these, and make a test under "realistic" usage conditions for welding:

https://hobbyking.com/media/catalog/product/cache/3/image/565x414/9df78eab33525d08d6e5fb8d27136e95/1/7/175937_9210000231-0.jpg

These are rated at 130C (pulse), which is 650A (!). Let's see what they will deliver in practice.
Title: Re: kWeld - "Next level" DIY battery spot welder
Post by: DBecker on July 18, 2017, 01:11:17 PM
I expect that the flux is primarily excluding atmospheric gases as the weld cools, preventing discoloring.  You might compare the effect to mineral oil and brake fluid.

Title: Re: kWeld - "Next level" DIY battery spot welder
Post by: maukka on July 18, 2017, 06:11:03 PM
I went with a Turnigy Graphene 6000mAh 5S1P 65 battery (https://hobbyking.com/en_us/turnigy-graphene-6000mah-5s1p-65c.html). According to Mooch (https://www.e-cigarette-forum.com/forum/blog-entry/lipo-pack-safety-grades-and-performance-table.7807/) they seem to be the best performers in high current applications (low internal resistance).
Title: Re: kWeld - "Next level" DIY battery spot welder
Post by: tatus1969 on July 18, 2017, 06:45:41 PM
I went with a Turnigy Graphene 6000mAh 5S1P 65 battery (https://hobbyking.com/en_us/turnigy-graphene-6000mah-5s1p-65c.html). According to Mooch (https://www.e-cigarette-forum.com/forum/blog-entry/lipo-pack-safety-grades-and-performance-table.7807/) they seem to be the best performers in high current applications (low internal resistance).
That is what I also ordered, but 5Ah/3S. Will be interesting to see my system running at 5S, that is still on my to do list.
Title: Re: kWeld - "Next level" DIY battery spot welder
Post by: BFX on July 19, 2017, 03:32:12 AM
Did you try power up your Gerät by MOT? For users which refuse buy an battery?  :box:
Title: Re: kWeld - "Next level" DIY battery spot welder
Post by: tatus1969 on July 19, 2017, 03:49:06 AM
Did you try power up your Gerät by MOT? For users which refuse buy an battery?  :box:
That'll not work easily because the module expects DC, the power switch is not bidirectional. One would need to add a diode with at 1000A pulse rating at the input, but that would also require a firmware extension that synchronizes firing with the rectified waveform.

The options that I can recommend at this time are a capable enough Lipo battery [that still has to be evaluated], a good car battery, and a suitable ultra capacitor.
Title: Re: kWeld - "Next level" DIY battery spot welder
Post by: tatus1969 on July 21, 2017, 12:28:14 AM
All the parts and tools for the new electrode system have arrived now. I will make a first complete build with video, but the first critical question is already answered: does the cable crimp work? See this picture of a cross section  :-+

(http://www.eevblog.com/forum/projects/guesses-on-what-i-am-attempting-here/?action=dlattach;attach=333744)

(http://www.eevblog.com/forum/projects/guesses-on-what-i-am-attempting-here/?action=dlattach;attach=333747)

Title: Re: kWeld - "Next level" DIY battery spot welder
Post by: Kjelt on July 21, 2017, 01:32:10 AM
 :-+ that looks as it is supposed to be, contact me please before shipping as it now looks like this crimp connection and new electrode system are really what I would like.
Title: Re: kWeld - "Next level" DIY battery spot welder
Post by: tatus1969 on July 21, 2017, 04:06:37 AM
:-+ that looks as it is supposed to be, contact me please before shipping as it now looks like this crimp connection and new electrode system are really what I would like.
If you like to change, or cancel and redo your order, please just give me a note. I can refund you whathever the difference is, and you don't need to worry about having to pay double shipping.

Cheers
Frank
Title: Re: kWeld - "Next level" DIY battery spot welder
Post by: tatus1969 on July 21, 2017, 04:17:50 AM
Here are pictures from the first build of the new electrode arrangement. The clamping mechanism works very well. I have done some welds with it, and it develops less heat than the previous design. I'll keep it like that and this is (or the parts for it) is what will be delivered when ordering it from the shop.

(http://www.eevblog.com/forum/projects/guesses-on-what-i-am-attempting-here/?action=dlattach;attach=333786)

(http://www.eevblog.com/forum/projects/guesses-on-what-i-am-attempting-here/?action=dlattach;attach=333788)

(http://www.eevblog.com/forum/projects/guesses-on-what-i-am-attempting-here/?action=dlattach;attach=333790)
Title: Re: kWeld - "Next level" DIY battery spot welder
Post by: Fraser on July 21, 2017, 08:47:07 AM
I decide that a simple hydraulic crimping tool would be useful to have in my tools collection so I have bought one this evening.
It is likely not that great for serious work but should meet my needs and those of this project. I also intend to use it as a mini hydraulic press once I have made up some flat face 'dies'.

There are two very similar looking versions on eBay. One is rated at 8T, whilst the other has a stronger head and is rated at 10T. The 8T comes with 8 dies and the 10T comes with 9 dies. I went for the 10T version.

The cost is £21.99 delivered from a UK warehouse. They are cheaper direct from China but I did not want to wait.

http://www.ebay.co.uk/itm/10-Ton-Hydraulic-Crimper-Crimping-Tool-Wire-Battery-Cable-Lug-Terminal-9-Dies-/322502047411?epid=1944118370&hash=item4b169eb6b3:g:LWEAAOSwT-FZCFV2 (http://www.ebay.co.uk/itm/10-Ton-Hydraulic-Crimper-Crimping-Tool-Wire-Battery-Cable-Lug-Terminal-9-Dies-/322502047411?epid=1944118370&hash=item4b169eb6b3:g:LWEAAOSwT-FZCFV2)

Fraser
Title: Re: kWeld - "Next level" DIY battery spot welder
Post by: cs.dk on July 22, 2017, 06:11:15 PM
Thanks for the link, Fraser.. I though hydraulic crimpers were a lot more expensive..  :-+
Had to buy this one; http://www.ebay.co.uk/itm/322465802286 (http://www.ebay.co.uk/itm/322465802286)
Title: Re: kWeld - "Next level" DIY battery spot welder
Post by: Fraser on July 22, 2017, 08:49:20 PM
Yes I was surprised as well. I considered the 16T version but it lacked the smaller 4,6 and 8mm dies that I would find useful. If I ever need to crimp the larger sizes I will certainly buy the 16T version as well.

Fraser
Title: Re: kWeld - "Next level" DIY battery spot welder
Post by: tatus1969 on July 22, 2017, 08:53:57 PM
I decide that a simple hydraulic crimping tool would be useful to have in my tools collection so I have bought one this evening.
It is likely not that great for serious work but should meet my needs and those of this project. I also intend to use it as a mini hydraulic press once I have made up some flat face 'dies'.

There are two very similar looking versions on eBay. One is rated at 8T, whilst the other has a stronger head and is rated at 10T. The 8T comes with 8 dies and the 10T comes with 9 dies. I went for the 10T version.

The cost is £21.99 delivered from a UK warehouse. They are cheaper direct from China but I did not want to wait.
Mine is a pure mechanical one, limited to 50qmm. It is less versatile as it has a fixed revolver style tool set, which is not milled but punched. But it has one advantage, it is quick to use.
Title: Re: kWeld - "Next level" DIY battery spot welder
Post by: cs.dk on July 22, 2017, 09:05:35 PM
For 4 and 6 mm i usually use DuraSeal ringterminals. Not lugs like the bigger (battery) ones. I've never seen a 8 mm2 cable. In Denmark we go from 6 mm2 to 10 mm2, that i'm aware of. Thats why i supposed i don't need em.

Mechanical ones are fine for most things, i use one at work everyday. But for a 70 mm2, you really need to push hard.
Title: Re: kWeld - "Next level" DIY battery spot welder
Post by: tatus1969 on July 22, 2017, 09:53:57 PM
For 4 and 6 mm i usually use DuraSeal ringterminals. Not lugs like the bigger (battery) ones. I've never seen a 8 mm2 cable. In Denmark we go from 6 mm2 to 10 mm2, that i'm aware of. Thats why i supposed i don't need em.

Mechanical ones are fine for most things, i use one at work everyday. But for a 70 mm2, you really need to push hard.
We had to do 6 x 150qmm on a ship once, to supply a 500kW hydraulic power pack. That was luckily done by the shipyard, they have no problem with that  ;)

the wire gauge that I use for the welder's electrode cable is an important part of the electrical system, also because it mainly defines the maximum pulse current level. If you choose to use cables with a larger cross section, then you'd have to pay attention to the total resistance budget, and make sure not to exceed the 2kA absolute maximum current level. Two days ago I made a(nother silly) mistake during my tests with the new electrode holder, by using a 5mm thick flat steel bar as weld material "simulator". I forgot to separate the electrodes by at least 20cm and placed them close to each other instead as I would do for a normal weld. I fired four or five times until I noticed that this was more than one second of continuous 1.2kA current flow. The battery didn't like it, and the Deans battery connector that is still there, even less. The welder has no problem with this, except that it realizes that the weld spot resistance is very very low and most of the energy goes elsewhere, which causes it to keep the current flowing until it times out or the energy was delivered at last.
Title: Re: kWeld - "Next level" DIY battery spot welder
Post by: cs.dk on July 22, 2017, 09:59:51 PM
Just courious about your product, but can you reliably weld 2 thicker plates together, lets say 0,8 mm sheet metal? If so, i could in deed be interested in one.
Title: Re: kWeld - "Next level" DIY battery spot welder
Post by: Fraser on July 22, 2017, 10:00:52 PM
Interesting to read about the 8mm2 size. That explains why that size is not present in the 8T version of my crimper :) I wanted the smaller sizes for when I do projects that require a metal tube to be crimped down onto a cable or rod. The tubes can be non standard diameters so having the 8mm2 die just looked to be useful :)

For smaller automotive type terminals I use the insulated ones and have the correct good quality crimping tool to compress them. The crimper even indents the plastic sleeve with the die details ! That crimping too was quite expensive but when dealing with automotive electrical connections, I take no chances.

I managed to get nice quality bootlace ferrule crimping tool a few years ago. Using bootlace ferrule crimps certainly tidies up my terminal block connections. Love that tool :)

Fraser
Title: Re: kWeld - "Next level" DIY battery spot welder
Post by: tatus1969 on July 23, 2017, 08:46:36 AM
Just courious about your product, but can you reliably weld 2 thicker plates together, lets say 0,8 mm sheet metal? If so, i could in deed be interested in one.
I'm afraid but I have no experience with that. Do you know what current levels and pulse times are required for that? The power switch of my welder electronics can reliably withstand 2kA for 200ms.

I found this interesting site: http://www.portablewelders.com/spot-welding-technical (http://www.portablewelders.com/spot-welding-technical)

It suggests at least 6kA for 200ms. The switch resistance of my welder is 120 microOhms. A current of 6kA would result in a power dissipation of 4.3kW, or 720W per transistor (assuming equal distribution, which is not the case). According to the datasheet of the used transistors, they allow a maximum pulse duration of 10ms at this power level. Which means: no, the kWeld circuit cannot do that for the required 200ms.

I managed to get nice quality bootlace ferrule crimping tool a few years ago. Using bootlace ferrule crimps certainly tidies up my terminal block connections. Love that tool :)
I'm still searching for the one that crimps well and is affordable. I have very good professional work experience with the Knipex 5512, that is in my opinion the one and only. Because that one is very expensive, I bought a "clone" for personal use - and I am quite disappointed. It is not machined precisely enough to do >=22AWG crimps.
Title: Re: kWeld - "Next level" DIY battery spot welder
Post by: Kjelt on July 23, 2017, 05:43:38 PM
The even more expensive knipex with six crimpsides was half price on amazon a half year back perhaps still. The reason was they made a new one that went two steps in awg further but who needs that. So scored one for 105 euros instead of al ost 200 and every crimp is a pure delight.
Title: Re: kWeld - "Next level" DIY battery spot welder
Post by: cs.dk on July 23, 2017, 05:45:46 PM
I'm afraid but I have no experience with that. Do you know what current levels and pulse times are required for that?

I have no idea - But you have a working device next to you ;)
Title: Re: kWeld - "Next level" DIY battery spot welder
Post by: tatus1969 on July 23, 2017, 06:57:53 PM
I'm afraid but I have no experience with that. Do you know what current levels and pulse times are required for that?

I have no idea - But you have a working device next to you ;)
That, yes. But no .8mm sheet metal :-//
Title: Re: kWeld - "Next level" DIY battery spot welder
Post by: Fraser on July 25, 2017, 06:47:18 AM
My 10T hydraulic lug crimping tool arrived today.

I must say I am very impressed with it. How do they manage to make such a relatively complex tool and sell it for so little ? The tool is well designed and made from what I can see. The pump action Is quick as apparently the design provides fast initial movement until resistance is felt, then the action slows down. Turning the pressure release knob results in very quick retraction of the lower die and piston. On the10T version, the die locating pins appear to be a better design than those seen on the 8T version. They snap into the die holders and the dies remain well retained and aligned.

For occasional use, I can certainly recommend this tool.

Fraser
Title: Re: kWeld - "Next level" DIY battery spot welder
Post by: tatus1969 on July 25, 2017, 08:26:07 AM
My 10T hydraulic lug crimping tool arrived today.

I must say I am very impressed with it. How do they manage to make such a relatively complex tool and sell it for so little ? The tool is well designed and made from what I can see. The pump actio. Is quick as apparently the desig. Provides fast initial movement until resistance is felt, then the action slows down. Turning the pressure release knob results in very quick retraction of the lower die and piston. On the10T version, the die locating pins appear to be a better design than those seen on the 8T version. They snap in to the die holders and the dies remain well retained and aligned.

For occasional use, I can certainly recommend this tool.

Fraser
I already regret it that I went for the cheaper option... |O
Title: Re: kWeld - "Next level" DIY battery spot welder
Post by: tatus1969 on July 25, 2017, 08:37:19 AM
A quick progress update on this project:
- production of 25 copies electronic module is progressing well. I had a delay of one week here waiting for the microprocessors from Arrow, but the parcel is now at customs clearance here in Germany (there was some annoyance regarding export control restrictions, I had to calm Mr Trump that I will not be building any rockets from them). The PCBs have been manufactured in the mean time.
- I have completed the firmware update functionality. All that is needed for that is a terminal program that can talk YMODEM (extraPutty and TeraTerm do this job well), an adapter cable (will be added to the shop for a few €), and an Arduino style FT232 USB->UART adapter configured for 3.3V operation (I will also sell them via the shop for convenience).
- I have designed a housing for the welder, see these pictures and please tell me how you like it. I'll upload it so that anyone can print it. I'll not be selling them in my shop, as I don't have a 3D printer.

I still wait for the new battery and some parts to make a video showing the new stuff, hopefully by this weekend  :D

Title: Re: kWeld - "Next level" DIY battery spot welder
Post by: Fraser on July 25, 2017, 08:45:03 AM
I like the case. Very nice design.

Thank you for the update on the first 25 modules :). I am in no great rush as I have other projects in flow along with selling off my excess test gear on eBay :) I will be happy to receive my module whenever it is convenient for you to ship it. I am just pleased that I have pre-ordered one to ensure I get it.

Fraser
Title: Re: kWeld - "Next level" DIY battery spot welder
Post by: tatus1969 on July 26, 2017, 05:51:18 PM
I think that it will still be possible to keep delivery by mid August, I will keep you updated. Had to call DHL customs yesterday to hear that they have high workload and would have eventually contacted me the next days because they need an EORI number from me.  :wtf:
Title: Re: kWeld - "Next level" DIY battery spot welder
Post by: tatus1969 on July 31, 2017, 10:08:24 AM
I've been working on the assembly manual, and have just uploaded a first (incomplete) version to the kicksurfer website. I have made this a downloadable product in my store that is free of charge for all registered users: https://www.kicksurfer.de/index.php/product/assembly-manual/ (https://www.kicksurfer.de/index.php/product/assembly-manual/)  That'll not help much against far east copiers, but maybe a bit...

And I have tested a different approach to manufacture the bus bars, the brass bars are just too expensive to finish. I have attached first pictures. These are laser-cut from 4mm x 12mm x 75mm aluminum bars. The first tests are very promising, the switch resistance goes up from 0.12 to 0.145 micro-ohms. That is just 25 micro-ohms more. They don't heat up noticeably during heavy firing.

Their price is quite good, so that for all people who have already purchased the brass bars, I can offer the following:
- if you have ordered them "raw" you can choose to receive the finished aluminum bars at no extra cost
- if you have ordered them "finished", I'll additionally refund the labor cost

Of course it'll also be okay to leave an order untouched.

I'll create a separate mail to all customers to ask for their wishes.

(https://endless-sphere.com/forums/download/file.php?id=219259)
(https://endless-sphere.com/forums/download/file.php?id=219263)
Title: Re: kWeld - "Next level" DIY battery spot welder
Post by: Fraser on July 31, 2017, 09:00:59 PM
My only concern regarding using Aluminium for the buss bars is the high reactivity of aluminium with the atmosphere. Aluminium oxide is a very poor conductor. Brass will also oxidise. Copper buss bars may be the best option, but also the most expensive.

I was considering what protection the bars may need to prevent such oxidisation becoming an issue over time. The old trick was to cover the area around the contact surface with an air excluder such as vaseline petrolium jelly. This may need to be considered but I do not think it is good to use it on the actual contact surface itself.

Fraser
Title: Re: kWeld - "Next level" DIY battery spot welder
Post by: Kjelt on July 31, 2017, 09:31:36 PM
I've been working on the assembly manual, and have just uploaded a first (incomplete) version to the kicksurfer website. I have made this a downloadable product in my store that is free of charge for all registered users: https://www.kicksurfer.de/index.php/product/assembly-manual/ (https://www.kicksurfer.de/index.php/product/assembly-manual/)  That'll not help much against far east copiers, but maybe a bit...
Great  :-+ , I just can't find the download button but ordered it so I expect you will mail it ?  :-//

Quote
And I have tested a different approach to manufacture the bus bars, the brass bars are just too expensive to finish.

What was the problem, the milling is it to tough or does the bit bite into the metal? It might be good as Fraser indicates to switch to Copper, but I will look into this myself.
Can you provide me (us) with the exact mechanical layout (thickness, length, wideness, and position of the holes and diameter) of the bars, than I can look at my local metaldump if I can find a suitable copper donorpiece and already start cutting it up and working on that  :) 
Do you think it would matter if the barr is made out of two or three parallel parts or perhaps made thicker, since it is the overall resistance that counts right?
Title: Re: kWeld - "Next level" DIY battery spot welder
Post by: Fraser on July 31, 2017, 09:41:30 PM
Kjelt,

You need to 'order' the manual and go through checkout as if you were buying it. You then see a link to click for the download in your checkout receipt. No charge is made to you and no card/PayPal is needed. It just requires you to log in.

Fraser
Title: Re: kWeld - "Next level" DIY battery spot welder
Post by: Kjelt on July 31, 2017, 09:42:35 PM
Yes thanks, the email had some delay but it is all clear now  :-+
Title: Re: kWeld - "Next level" DIY battery spot welder
Post by: tatus1969 on August 01, 2017, 12:06:42 AM
Kjelt,

You need to 'order' the manual and go through checkout as if you were buying it. You then see a link to click for the download in your checkout receipt. No charge is made to you and no card/PayPal is needed. It just requires you to log in.

Fraser
thanks for helping me out  :D
Title: Re: kWeld - "Next level" DIY battery spot welder
Post by: tatus1969 on August 01, 2017, 01:24:32 AM
My only concern regarding using Aluminium for the buss bars is the high reactivity of aluminium with the atmosphere. Aluminium oxide is a very poor conductor. Brass will also oxidise. Copper buss bars may be the best option, but also the most expensive.

I was considering what protection the bars may need to prevent such oxidisation becoming an issue over time. The old trick was to cover the area around the contact surface with an air excluder such as vaseline petrolium jelly. This may need to be considered but I do not think it is good to use it on the actual contact surface itself.
I've got the same feedback on other places, and I have started investigating it. I found a shop that sells galvanic articles, and it would be possible to add chemical zinc, and then galvanize with gold. That would be a good match for the gold PCB traces.

On the other hand, I have built an audio amplifier decades ago, and I still have the bulk capacitors with screw terminals that are connected with aluminum bars. The capacitor's screw terminals were made from tinned brass.

That makes me think: would it prevent contact corrosion if I would order tinned PCB's instead of gold plated next time?

What was the problem, the milling is it to tough or does the bit bite into the metal? It might be good as Fraser indicates to switch to Copper, but I will look into this myself.
Can you provide me (us) with the exact mechanical layout (thickness, length, wideness, and position of the holes and diameter) of the bars, than I can look at my local metaldump if I can find a suitable copper donorpiece and already start cutting it up and working on that  :) 
Do you think it would matter if the barr is made out of two or three parallel parts or perhaps made thicker, since it is the overall resistance that counts right?
I indeed had problems with drills biting into the metal, but meanwhile I have specialized soft metal drills that perform much better. The work steps on the brass bars are the following:
- cut to length
- measure and centerpunch all drill positions (I will use a template instead for "mass" production)
- drill 4.5mm holes
- drill 6.5mm holes
- deburr with countersink drill
- sand all faces

That sums up, wich was why I decided to set the price for that work relatively high. Also to prevent myself from drowning in machining work.

Here are the dimensions of the original brass bars. The new aluminm bar is identical but is only 4mm thick (the maximum that my provider can laser with this contour).

(http://www.eevblog.com/forum/projects/guesses-on-what-i-am-attempting-here/?action=dlattach;attach=336868)
Title: Re: kWeld - "Next level" DIY battery spot welder
Post by: Kjelt on August 01, 2017, 01:54:27 AM
Thanks for the info Frank  :-+ Itsure takes time if you do all those steps,almost time for a CNC  ;)
Title: Re: kWeld - "Next level" DIY battery spot welder
Post by: tatus1969 on August 01, 2017, 01:56:13 AM
almost time for a CNC  ;)
definitely!!
Title: Re: kWeld - "Next level" DIY battery spot welder
Post by: Fraser on August 01, 2017, 02:11:28 AM
I have been looking at the cost and availability of 12.7mm x 12.7mm copper bar. In the UK it will cost me around £10 inc postage. As I am doing the machining myself I am tempted to go with copper bars. I may find some thinner copper bar cheaper as 12.7 x 12.7 is overkill. One nice property of copper is that its ovidation does not interfere with conduction. Hence its use in building utility mains bus bars :)

Fraser
Title: Re: kWeld - "Next level" DIY battery spot welder
Post by: kony on August 01, 2017, 03:47:36 AM
Get the aluminium busbars nickel plated. Cheap & effective corrosion protection.
Title: Re: kWeld - "Next level" DIY battery spot welder
Post by: tatus1969 on August 01, 2017, 06:31:25 AM
I just ordered some bottles of chemical nickel plating solvent, it is not very expensive and I will treat all sold aluminum bus bars with that. For aluminium, they sell an "activator" fluid.
Title: Re: kWeld - "Next level" DIY battery spot welder
Post by: tatus1969 on August 01, 2017, 06:35:57 AM
I have been looking at the cost and availability of 12.7mm x 12.7mm copper bar. In the UK it will cost me around £10 inc postage. As I am doing the machining myself I am tempted to go with copper bars. I may find some thinner copper bar cheaper as 12.7 x 12.7 is overkill.
The  wisdom A Lot Helps A Lot is in fact true here  ;) Anyhow, I have calculated the ohmic resistance of the new 4x12x75mm alu bus bars with 48 micro ohms...

One nice property of copper is that its ovidation does not interfere with conduction. Hence its use in building utility mains bus bars :)
The problem was that I have a cheap laser cutting service at hand, and they don't offer copper. They're already ordered as aluminum.
Title: Re: kWeld - "Next level" DIY battery spot welder
Post by: tatus1969 on August 02, 2017, 08:25:19 AM
Just wanted to share this with you before going to sleep. Today the XT90 plugs arrived that I was waiting for. As the battery came with them, I wanted to test the suitability of these before cutting the wires and soldering XT150. First conclusion: they do not support insertion of AWG8.

What is more interesting is the first data that I captured from the new Turnigy nano-tech 3S / 5Ah / 130C (=650A) battery. The welder has measured an impressive current of 1230A. The oscilloscope diagram taken from (almost) the battery terminals shows a voltage drop of 6.56V at this current. This results in an internal resistance of these beasts of only 5.3mOhm. That is comparable to what is achievable with supercapacitors. Now the battery has to show how well it likes currents at this level (as specified, this is only 1.9 times of rated current). I will do a stress test in a new video this weekend.

(https://endless-sphere.com/forums/download/file.php?id=219329)

(https://endless-sphere.com/forums/download/file.php?id=219328)
Title: Re: kWeld - "Next level" DIY battery spot welder
Post by: Fraser on August 02, 2017, 09:04:29 AM
I have ordered those XT90 plug sets for my unit. I got a good deal on 10 pairs of connectors, so plenty to experiment with.

I intend to use a pair of the contacts in parallel for each power cable from the battery.  I can split the cable strands into two smaller bunches to suit the connector.

Fraser
Title: Re: kWeld - "Next level" DIY battery spot welder
Post by: fuzzoli on August 04, 2017, 09:33:08 PM
Will the bare boards be available for purchase?  I noticed only the fully assembled boards are listed in the shop.  Thanks!
Title: Re: kWeld - "Next level" DIY battery spot welder
Post by: tatus1969 on August 04, 2017, 11:37:11 PM
Will the bare boards be available for purchase?  I noticed only the fully assembled boards are listed in the shop.  Thanks!
The bare boards would be no problem, but I decided to protect the firmware code against Chinese copying (encryption + special bootloader), because it has a number of novel features and I don't want to make it too easy for them. I don't have a QFP48 ZIF socket here [yet], so I cannot pre-program the bare microcontrollers.
Title: Re: kWeld - "Next level" DIY battery spot welder
Post by: Fraser on August 05, 2017, 03:26:04 AM
I ordered some 12.7mm x 12.7mm x 300mm square copper bar today. In the UK it cost me £12 delivered. I think this excellent project deserves decent buss bars though :) I am considering tapping the holes M4 to increased the contact area between the bolt head and the copper buss bar. That may be overkill though. At least copper is easy to work with :)

I also ordered some nice large 5mm RC EC5 connector pairs that are rated at 120A continuous and they take 10awg cables :)

Fraser
Title: Re: kWeld - "Next level" DIY battery spot welder
Post by: tatus1969 on August 05, 2017, 03:40:23 AM
Will the bare boards be available for purchase?  I noticed only the fully assembled boards are listed in the shop.  Thanks!
The bare boards would be no problem, but I decided to protect the firmware code against Chinese copying (encryption + special bootloader), because it has a number of novel features and I don't want to make it too easy for them. I don't have a QFP48 ZIF socket here [yet], so I cannot pre-program the bare microcontrollers.
I'm also not sure if it is worth it. I just uploaded the part list (except 0603 resistors / capacitors) to Digikey, the calculated total is 60.36€ plus VAT. I would sell the programmed microprocessor for 10€, and my price for a bare board would be another 10€, so there is ~20€ to save, which would be quickly eaten up by shipping costs.
Title: Re: kWeld - "Next level" DIY battery spot welder
Post by: tatus1969 on August 05, 2017, 04:07:47 AM
I ordered some 12.7mm x 12.7mm x 300mm square copper bar today. In the UK it cost me £12 delivered. I think this excellent project deserves decent buss bars though :) I am considering tapping the holes M4 to increased the contact area between the bolt head and the copper buss bar. That may be overkill though. At least copper is easy to work with :)
I think it's safe to say that they will not be the weakest link of the chain  8)

I also ordered some nice large 5mm RC EC5 connector pairs that are rated at 120A continuous and they take 10awg cables :)
I just did a measurement with the XT90 connectors that I forgot in the first place. The voltage drop across one contact pair at 1205A is just 46mV, which results in a contact resistance of 38 micro ohms, or 76 micro ohms round trip. The power's dissipation during the pulse is then 55W.

I'll repeat that with the XT150, but I think that this value is already good enough, considered that the system will have a duty cycle of maybe 20% max. The only disadvantage is that it only fits cables up to 6.5mm diameter, and that the soldering terminal is too small for AWG8 cross section either. I will stick with XT150, that is perfect for this application, although a bit expensive. And maybe add an XT90 option if there is enough interest.
Title: Re: kWeld - "Next level" DIY battery spot welder
Post by: Fraser on August 05, 2017, 04:14:05 AM
Tatus1969,

In case I have not said it before, thank you very much for not only making your design available to us, but also for selling it at such a reasonable cost. I know that the profit margin is very slim and it is little reward for all your hard work, both in developing the design and the work required to sell us a kit.

I know it does not pay the bills, but you have my sincerest thanks for this act of kindness  :-+

Fraser
Title: Re: kWeld - "Next level" DIY battery spot welder
Post by: tatus1969 on August 05, 2017, 04:28:36 AM
Tatus1969,

In case I have not said it before, thank you very much for not only making your design available to us, but also for selling it at such a reasonable cost. I know that the profit margin is very slim and it is little reward for all your hard work, both in developing the design and the work required to sell us a kit.

I know it does not pay the bills, but you have my sincerest thanks for this act of kindness  :-+

Fraser
My reward will not (only) be the paid bills, but the (hopefully positive) feedback from you folks making use of it, talking about it, and maybe doing the one or other review. I just had a job interview today (I had quit my last job because I didn't enter into a supporting environment when taking it two years ago), and one of the things that I said was that I am looking for a job where I can do something meaningful. (They do custom electric vehicle conversions [their first project was a DeLoran - yes it can do 88mph], and I'm very excited.) I keep driving this project because I have the same feeling here as well.

p.s. and if I'm lucky it will get me the Rohde&Schwarz oscilloscope that Dave is giving away - I participated and of course showed this project among others 8)
Title: Re: kWeld - "Next level" DIY battery spot welder
Post by: Kjelt on August 05, 2017, 07:28:34 AM
Tatus1969,
In case I have not said it before, thank you very much for not only making your design available to us, but also for selling it at such a reasonable cost. I know that the profit margin is very slim and it is little reward for all your hard work, both in developing the design and the work required to sell us a kit.
I know it does not pay the bills, but you have my sincerest thanks for this act of kindness  :-+
Fraser
+1 very well worded,
Also already my big thanks to you Frank for sharing this great project  :-+  :-+  :-+
Title: Re: kWeld - "Next level" DIY battery spot welder
Post by: tatus1969 on August 05, 2017, 07:51:00 PM
Also already my big thanks to you Frank for sharing this great project  :-+  :-+  :-+
Thanks alot, it is a bit overwhelming :D I accept rewards in the form of honest public feedback and reviews  ;)
Title: Re: kWeld - "Next level" DIY battery spot welder
Post by: tatus1969 on August 10, 2017, 03:45:55 PM
I am busy with the next product video, and realized that the new probe design is now thermally the limiting factor. Too bad as it is the only part that you need to hold. Therefore I started a third iteration, the idea is to use 6mm copper rod and thread that down to M5. The holder will be threaded as well, which means that you then can screw in the electrodes. That should significantly reduce ohmic losses there. Parts ordered, I'll keep you updated.
Title: Re: kWeld - "Next level" DIY battery spot welder
Post by: Kjelt on August 12, 2017, 06:08:08 AM
I just stumbled upon a box with 140 elcos 2200uF/63V
I guess even if I place them all parallel it still would not hold sufficient energy to do a proper weld?
Title: Re: kWeld - "Next level" DIY battery spot welder
Post by: tatus1969 on August 12, 2017, 07:31:51 AM
I just stumbled upon a box with 140 elcos 2200uF/63V
I guess even if I place them all parallel it still would not hold sufficient energy to do a proper weld?
Could be worth a try, resistance will most probably be low enough when paralleling all of them. Do you have that data? It may even be necessary to add more cable length to keep total resistance high enough to not exceed the 2000A limit.

You should use as much voltage as possible, my design should be good for up to 30V, although not tested yet.

The stored energy at 30V is 140J, the system efficiency with my new battery is 15% to have a number to start with. That would allow weld energies up to 20J. Close, but not enough I think.

I am concentrating on the Turnigy nanotech 3S 5Ah 130C. I stress tested it two days ago while shooting video, and then accidentially deleted the entire footage, 30Gb... :?

What I can already say that a complete discharge cycle resulted in approx 900 pulses of 30J into 1mOhm, and an accumulated pulse time of 15 seconds, at a current of 1400A average. And most importantly, absolutely no visible battery swell.

That is enough for me to say that I can recommend them for my welder. The only limiting factor is that they have only AWG10 wires, which limits pulse repetition rate. The battery temperature needs to be checked as well, I could not run my rapid firing test in one go, there were quite a few cooling breaks.
Title: Re: kWeld - "Next level" DIY battery spot welder
Post by: Kjelt on August 12, 2017, 07:38:07 AM
Thanks for the info, i don't have the esr for the elco unfortunately but can measure it. But since it is a normal series (cheap) the esr will probably not be low enough. I will check the turnigy out, tips where to buy them? Also going to need a charger. I am not running any production just a few cells here and then and perhaps some other application.
Title: Re: kWeld - "Next level" DIY battery spot welder
Post by: tatus1969 on August 12, 2017, 08:29:56 AM
Thanks for the info, i don't have the esr for the elco unfortunately but can measure it. But since it is a normal series (cheap) the esr will probably not be low enough. I will check the turnigy out, tips where to buy them? Also going to need a charger. I am not running any production just a few cells here and then and perhaps some other application.
You can get them here:
https://hobbyking.com/en_us/turnigy-nano-tech-5000mah-3s-65-130c-lipo-pack.html

The charger that I use is SkyRC RS16, available from many sources. That can do up to 6S, which is not needed here.
Title: Re: kWeld - "Next level" DIY battery spot welder
Post by: tatus1969 on August 13, 2017, 10:08:41 PM
The manufacturing of the pre-ordered kWeld electronics is running well, and I expect to have received everything by end of next week. I will start testing and programming them right after arrival and expect to be able to ship in week 34. If you have pre-ordered one, then I hope that you like working with the system as much as I do, and please give me your honest feedback.

In the meantime, there have been a few more additions and improvements. I am showing them on Youtube:

https://youtu.be/rQnODV4VQjU (https://youtu.be/rQnODV4VQjU)

- the system firmware has been extended by a bootloader that allows firmware updates via a simple serial connection. All you need is a terminal program that supports YMODEM file transfers, and an adapter that is available in the shop: https://www.kicksurfer.de/index.php/product/kweld-firmware-update-tool/ (https://www.kicksurfer.de/index.php/product/kweld-firmware-update-tool/)
(https://endless-sphere.com/forums/download/file.php?id=219979)

- a first sample of a 3D printed housing has arrived, and I am currently testing it. I plan to make it available in the shop, and also to provide the 3D data for free to enable you printing your own.
(https://endless-sphere.com/forums/download/file.php?id=219977)

- I have tested a new type of Lipo battery for use with the welder: Turnigy nano-tech 3S 5Ah 130C (https://hobbyking.com/en_us/turnigy-nano-tech-5000mah-3s-65-130c-lipo-pack.html (https://hobbyking.com/en_us/turnigy-nano-tech-5000mah-3s-65-130c-lipo-pack.html)). This is the first battery that has survived more than one hour of continuous torture testing without any measurable swell or other damage. This is so far the only Lipo that I can definitely recommend to you. You can download the torture test results here: https://www.kicksurfer.de/wp-content/uploads/2017/08/kWeld-torture-test.zip (https://www.kicksurfer.de/wp-content/uploads/2017/08/kWeld-torture-test.zip)

- the electrode system needed to go through a third iteration. The battery torture test showed that the previous system had a too high ohmic resistance and was heating up too quickly. As a side effect, I could again significantly reduce the involved machining effort. The new system only requires crimping the cable to a brass tube, thread-tapping tube and copper electrode, and heat shrinking an isolation. This also makes electrode replacement easier than ever before.
(https://endless-sphere.com/forums/download/file.php?id=219978)

As the previous electrode design did not meet my quality requirements, I will inform all pre-order customers that they will receive the new design instead at no additional cost.
Title: Re: kWeld - "Next level" DIY battery spot welder
Post by: Kjelt on August 14, 2017, 03:02:18 AM
 :-+ very nice improvements again.
Title: Re: kWeld - "Next level" DIY battery spot welder
Post by: mzzj on August 14, 2017, 07:14:37 PM
I just stumbled upon a box with 140 elcos 2200uF/63V
I guess even if I place them all parallel it still would not hold sufficient energy to do a proper weld?
Sufficient energy but at wrong voltage level. (unless you couple them with transformer)
60 volts give you more likely loud bang and sparks but poor or no weld at all. And charged to ~20 volts you don't have enough energy.
Title: Re: kWeld - "Next level" DIY battery spot welder
Post by: Marco on August 15, 2017, 07:16:42 PM
Why would 60v not work? Too much energy in too little time?
Title: Re: kWeld - "Next level" DIY battery spot welder
Post by: Kjelt on August 15, 2017, 08:06:27 PM
Why would 60v not work? Too much energy in too little time?
the kWeld was designed for max. 30V , I think the Mosfets are the limitation ?
But it does not matter, a carbattery would go nicely also. The batterypacks are out of stock so I have to look at another alternative.
Title: Re: kWeld - "Next level" DIY battery spot welder
Post by: Fraser on August 15, 2017, 08:11:33 PM
I am going to try a large capacity sealed lead axis 12V battery with my kWeld. Hopefully it will be up to the job and less likely to complain than a LiPo.

From memory I have brand new 15Ah and 36Ah SLA 12V Gel batteries.

Fraser
Title: Re: kWeld - "Next level" DIY battery spot welder
Post by: mzzj on August 15, 2017, 10:11:11 PM
Why would 60v not work? Too much energy in too little time?
Something like that. Not sure about the exact physic behind it but for sure it didn't seem to work. (tried some years ago)
Title: Re: kWeld - "Next level" DIY battery spot welder
Post by: tatus1969 on August 16, 2017, 12:19:41 AM
Why would 60v not work? Too much energy in too little time?
Something like that. Not sure about the exact physic behind it but for sure it didn't seem to work. (tried some years ago)
I can imagine that too much current can cause problems because the pulse time control of existing systems may be too coarse to achieve the ultra short pulses that will be necessary for this. The kWeld firmware pulse control loop runs at a 10 microsecond interval and should be able to handle this as well. The other problem that I can imagine is that a current that is too high may instantly blow away some material and ignite an electric arc instead, eating more material.

brand new 15Ah and 36Ah SLA 12V Gel batteries.
Do you have the equipment to measure those's ESR? An oscilloscope and a power resistor of 0.5  ~ 1.0 ohm that you can sacrifice would be enough.

I just ordered six of these: Maxwell BCAP0310 P270 T10 supercapacitors. They have an ESR of 2.2 milliOhm, and I calculated that four of them in series should already do the job for pulses up to 50 joules. That would be another cost effective solution, as these cost only 10€ each.
Title: Re: kWeld - "Next level" DIY battery spot welder
Post by: tatus1969 on August 16, 2017, 01:42:41 AM
I've got some work on my desk   :D

(https://endless-sphere.com/forums/download/file.php?id=220172)
Title: Re: kWeld - "Next level" DIY battery spot welder
Post by: Marco on August 16, 2017, 01:49:40 AM
Something like that. Not sure about the exact physic behind it but for sure it didn't seem to work. (tried some years ago)

Too short a pulse might evaporate metal before the melt can spread I guess.
Title: Re: kWeld - "Next level" DIY battery spot welder
Post by: tatus1969 on August 18, 2017, 05:29:45 AM
Something like that. Not sure about the exact physic behind it but for sure it didn't seem to work. (tried some years ago)

Too short a pulse might evaporate metal before the melt can spread I guess.
It is not the voltage that needs to be limited but the current. I got good results at 1000A with the old Lipo, and it is also good with the new Lipo and 1400A. The kWeld power switch is software-limited to 2000A. The current is determined only by the combined system ESR, and the weld spot resistance. We'll have to live with zero ohm weld spot resistance. When using a 12V power supply, and limiting the current to 1700A, this yields a minimum system resistance of 7 milliOhms. Double that resistance, and you can use a 24V supply. But there is no real benefit in going to higher voltages, you'll only reduce system efficiency further. The 12V system delivers approx 15% of the energy drawn from the battery into a 1 milliOhm weld spot, the other 85% are wasted in battery, power switch and cabling.
Title: Re: kWeld - "Next level" DIY battery spot welder
Post by: Fraser on August 19, 2017, 01:40:30 AM
Another piece of my 'kWeld parts collection' arrived today..... some 5mm copper rod to make the new threaded version of the probes. I thought I would psot some pictures of my parts collection for this project. I bought my own parts rather than the official kWeld parts kits as I want to experiment and will need more material. For many people without the bits in their parts bins, the kWeld kits of parts make better financial sense.

I do like the foot pedal I found though. It was actually bought to add foot pedal control to my Chinese Tab welder but it can now serve both that and the kWeld. The brass hollow rod was being sold by a chap who had many in stock. They look like long stand-off's, maybe left overs from a project. They are all 100mm long and have finished ends. I will be having 100mm long probes for my kWeld.

I also purchased a selection of high current connectors for various uses. I followed the OP's recommendation and bought the XT150 types as well as the EC5's.

The battery will be a decent capacity Yuasa 12V sealed lead acid gel type that I already have as that is quite a saving.

Fraser
Title: Re: kWeld - "Next level" DIY battery spot welder
Post by: tatus1969 on August 19, 2017, 08:18:55 AM
I will be having 100mm long probes for my kWeld.
:-+ but make sure to fill the brass tube entirely with the electrode copper, or it may have excessive resistance / heating.
Title: Re: kWeld - "Next level" DIY battery spot welder
Post by: SirJMD on August 21, 2017, 06:24:59 PM
I'd love to see a "shot counter". This would make it great for evaluating the state of the battery (or other power source). If the number of shots starts to decrease dramatically, we know the battery is dying.
Title: Re: kWeld - "Next level" DIY battery spot welder
Post by: tatus1969 on August 21, 2017, 11:22:49 PM
I'd love to see a "shot counter". This would make it great for evaluating the state of the battery (or other power source). If the number of shots starts to decrease dramatically, we know the battery is dying.
Thanks, very good idea! I've directly put this on my todo list. I'll make it an input energy meter, and I'll also implement a function that measures the battery ESR.
Title: Re: kWeld - "Next level" DIY battery spot welder
Post by: SirJMD on August 22, 2017, 08:38:10 PM
I'd love to see a "shot counter". This would make it great for evaluating the state of the battery (or other power source). If the number of shots starts to decrease dramatically, we know the battery is dying.
Thanks, very good idea! I've directly put this on my todo list. I'll make it an input energy meter, and I'll also implement a function that measures the battery ESR.

Sounds great! I'm looking forward to receving the kWeld and start testing.

I was thinking of ordering some supercapacitors and use those as a power source. I'm unsure how the capacitors will cope with the high discharge rates. The Maxwell ones I've looked at is rated at 250A maximum, with an internal resistance of 2,2 mOhm and 2,5V nominel.

I was thinking of using 6 in series, which would result in just under 60F at 15V, for a total of ~6.5kJ. I'm not sure if the current capabilities of these are sufficient.
Title: Re: kWeld - "Next level" DIY battery spot welder
Post by: tatus1969 on August 25, 2017, 07:16:17 AM
I was thinking of ordering some supercapacitors and use those as a power source. I'm unsure how the capacitors will cope with the high discharge rates. The Maxwell ones I've looked at is rated at 250A maximum, with an internal resistance of 2,2 mOhm and 2,5V nominel.

I was thinking of using 6 in series, which would result in just under 60F at 15V, for a total of ~6.5kJ. I'm not sure if the current capabilities of these are sufficient.
That must be the previous version of their Boostcap parts, the current ones have 2.7V. It appears that I have almost the same type of cells here: BCAP0310 P270 T10, these have 2.2mR as well.

I am trying to use as few of them as possible, and will start with four. They have ridiculously strong solder tabs, and I had to first get a suitable soldering iron, the 80W Weller didn't blend...

I realized though that, if it works good enough at all, these will only be able to deliver a single pulse. And as you don't really want to wait for several seconds for them to recharge, we will need quite a decent power supply. I think a 400-600W ATX power supply will do, but we need a current limiter betwen PSU and capacitors, because these normally operate in hiccup mode and that is not what we want here. I am thinking of a boost converter with input current measurement, but it will need to be quite beefy. Do you have another idea of how to accomplish this? I think any dissipative solution is out at these power levels.
Title: Re: kWeld - "Next level" DIY battery spot welder
Post by: tatus1969 on August 25, 2017, 07:20:39 AM
It was quite some work, but I have managed to ship all orders in time (week 34) as promised! Thank you for your patient waiting, and I am curious about your feedback.
Title: Re: kWeld - "Next level" DIY battery spot welder
Post by: Kjelt on August 25, 2017, 07:30:19 AM
For the supercaps, how about those carbattery psu's they are quite beefy and with a good voltage (13-14V).

I am eagerly waiting for the postman to show up with the kWeld although I do not have a suitable powersource yet.
Title: Re: kWeld - "Next level" DIY battery spot welder
Post by: Fraser on August 25, 2017, 07:45:17 AM
Regarding power sources, one of the cheapest is a small car battery as fitted in say a Classic Mini. In the UK, a decent one is only about £25. They are built for abuse as cars are not the kindest loads or chargers ! Car battery chargers are also cheap and available. Basic solid technology, if a little agricultural :)

Wet batteries are risky though as there is the acid spill and hydrogen accumulation explosion risk.... especially when heavily loading them with a spark producing welder ! I am going to use heavy duty 12V Gel batteries in a well ventilated area.

Fraser
Title: Re: kWeld - "Next level" DIY battery spot welder
Post by: tatus1969 on August 25, 2017, 07:51:26 AM
For the supercaps, how about those carbattery psu's they are quite beefy and with a good voltage (13-14V).
I just checked ebay for that, you only get 6A output current models when limiting the price to 20€. At that current level recharging would last 139 seconds (5 x 310F charged to 13.5V)...

If we want the system to be able to fire a 50J weld once a second, and the system efficiency if 15% (based on measurements with my new battery), then we need to suppy 50 / 0.15 = 333W of continuous power. For my solution with a current limiting step-down converter with lets's say 90% efficiency, this meand that a 12V power source needs to be able to deliver 333 / 12 / 0.9 = 30.8A. A >= 650W ATX PSU should be able deliver this, these start at 30-40€.
Title: Re: kWeld - "Next level" DIY battery spot welder
Post by: Kjelt on August 25, 2017, 07:56:50 AM
I am not sure if a pc psu likes these giant currentjumps, they might shut down on OCP.
 Perhaps some form of current limiter between the psu and supercaps ?
Title: Re: kWeld - "Next level" DIY battery spot welder
Post by: tatus1969 on August 25, 2017, 08:07:53 AM
Perhaps some form of current limiter between the psu and supercaps ?
That's exactly what I am talking about in the previous posts  ;D
Title: Re: kWeld - "Next level" DIY battery spot welder
Post by: Marco on August 26, 2017, 08:37:01 AM
It is not the voltage that needs to be limited but the current.

With this circuit, a low dynamic resistance thyristor isn't terribly expensive and could handle the current.

I am not sure if a pc psu likes these giant currentjumps, they might shut down on OCP.
 Perhaps some form of current limiter between the psu and supercaps ?

Easier to use a PSU with a current limiter rather than an ATX PSU. If you want to charge at max power with an ATX supply you would have to use a buck converter with an input filter to smooth the current.
Title: Re: kWeld - "Next level" DIY battery spot welder
Post by: tatus1969 on August 26, 2017, 09:34:04 AM
With this circuit, a low dynamic resistance thyristor isn't terribly expensive and could handle the current.
You cannot switch DC with a thyristor.

Easier to use a PSU with a current limiter rather than an ATX PSU. If you want to charge at max power with an ATX supply you would have to use a buck converter with an input filter to smooth the current.
I am looking for the solution at lowest possible price. The buck converter will cost maybe 20-30€, the ATX PSU another 30-40€, totaling 50-70€. Can you can recommend a 12V / 40A PSU that can easily be sourced and meets this price.
Title: Re: kWeld - "Next level" DIY battery spot welder
Post by: Marco on August 26, 2017, 09:32:26 PM
You cannot switch DC with a thyristor.

That's not how capacitive discharge works. You charge the capacitor with a low current switching converter, then you dump all the energy from the capacitor with the thyristor. When the current drops to zero the thyristor turns off.

Quote
I am looking for the solution at lowest possible price. The buck converter will cost maybe 20-30€, the ATX PSU another 30-40€, totaling 50-70€. Can you can recommend a 12V / 40A PSU that can easily be sourced and meets this price.

Hmm, looking around, it's hit or miss to find a Mean Well clone which can be easily modded into constant current. Some have current limiting, some shut down when they detect a fault ... not like they have accurate data sheets :/
Title: Re: kWeld - "Next level" DIY battery spot welder
Post by: tatus1969 on August 27, 2017, 01:27:10 AM
That's not how capacitive discharge works. You charge the capacitor with a low current switching converter, then you dump all the energy from the capacitor with the thyristor. When the current drops to zero the thyristor turns off.
The main idea behind my welder is that it measures the amount of energy that is dumped into the weld spot, and stops the current when a user adjustable threshold is exceeded. This provides very consistent welds. This can only be achieved with MOSFETs.
Title: Re: kWeld - "Next level" DIY battery spot welder
Post by: SirJMD on August 27, 2017, 04:37:01 AM
That's not how capacitive discharge works. You charge the capacitor with a low current switching converter, then you dump all the energy from the capacitor with the thyristor. When the current drops to zero the thyristor turns off.
The main idea behind my welder is that it measures the amount of energy that is dumped into the weld spot, and stops the current when a user adjustable threshold is exceeded. This provides very consistent welds. This can only be achieved with MOSFETs.

Aha. I was wondering why you didn't use thyristors instead of MOSFETs, since they come in rather large packages that can handle several thousands of amps, while being relatively cheap.

Have you looked into forced commutation? Possibly a class D commutation setup might do it.
Title: Re: kWeld - "Next level" DIY battery spot welder
Post by: tatus1969 on August 27, 2017, 05:55:53 AM
Aha. I was wondering why you didn't use thyristors instead of MOSFETs, since they come in rather large packages that can handle several thousands of amps, while being relatively cheap.

Have you looked into forced commutation? Possibly a class D commutation setup might do it.
I had considered them, and there were several reasons why I decided against them:
- a 300A SCR would probably have done the job, these are ~30€ which is same cost as I have now
- I was concerned if I would be able to design a reliable forced communitation circuit - it it fails to turn off the SCR, then the fuse is the last hope to prevent something from catching fire
- the voltage drop of the SCR would probably be 2V @ 1000A, which is more than 10 times of what it is now
- they are much bigger and I wanted to integrate everything on a circuit board
- last but not least, my knowledge of MOSFETs is several decades higher than that of SCRs
Title: Re: kWeld - "Next level" DIY battery spot welder
Post by: Kjelt on August 27, 2017, 07:07:45 PM
Awaiting the package this week so I need to do some scouting for powersources.

Does the wire need to be silicon?
I can find 10 and 16mm2 awg7 and awg5 i believe in flexible wire for in the power cabinet.
I probably gonna buy some anyway for the next item:

Yesterday evening I met someone who might be interested in swapping my R&S HF generator that is eating dust since I do nothing with hf, against a 1500W 45A  digital VC and CC controlled power supply  8)

If that deal is happening then I am seriously looking for some 5 or 6 supercapacitors, I am only not sure how many F's they should have ?  Any link besides Ebay or suggestion is welcome  :)

I also see some protection boards with loadbalancing and current limiting, what is that about? Since we do not want current limiting in this application is it safe to use supercapacitors this way or could they also explode as LiPos?
Title: Re: kWeld - "Next level" DIY battery spot welder
Post by: JohnG on August 28, 2017, 01:00:55 AM
Aha. I was wondering why you didn't use thyristors instead of MOSFETs, since they come in rather large packages that can handle several thousands of amps, while being relatively cheap.

Have you looked into forced commutation? Possibly a class D commutation setup might do it.
I had considered them, and there were several reasons why I decided against them:
- a 300A SCR would probably have done the job, these are ~30€ which is same cost as I have now
- I was concerned if I would be able to design a reliable forced communitation circuit - it it fails to turn off the SCR, then the fuse is the last hope to prevent something from catching fire
- the voltage drop of the SCR would probably be 2V @ 1000A, which is more than 10 times of what it is now
- they are much bigger and I wanted to integrate everything on a circuit board
- last but not least, my knowledge of MOSFETs is several decades higher than that of SCRs

At low voltage, it is very tough to beat a power MOSFET. Cost is way down from where it used to be, they are robust, and fully controllable. Any bipolar device (SCRs included) have a saturation voltage of a few tenths of a volt, at least. Since this is a pretty slow application, the large capacitance of multiple high-current MOSFETs should not be a problem.

I don't have a ton of experience with thyristors, either, but what little I have had made me think that they are a lot more finicky and less straightforward than they seem.

John
Title: Re: kWeld - "Next level" DIY battery spot welder
Post by: anishkgt on August 28, 2017, 02:32:56 AM
I've designed one with a Microwave Oven Transformer and and another version on its way. There the switch on time is always controlled  with a dual SCR in a back to back configuration.

SCR or thyristors are basically used with AC voltages as they switch OFF at zero cross but when dealing with dc supply MOSFTETS do a better job.
Title: Re: kWeld - "Next level" DIY battery spot welder
Post by: tatus1969 on August 28, 2017, 03:27:28 AM
Does the wire need to be silicon?
I can find 10 and 16mm2 awg7 and awg5 i believe in flexible wire for in the power cabinet.
Haven't heard of silicon wires yet  8) Are they any good? :P That reminds me of a scene from Terminator 2: in the German translation, Arnie is referring to his high performance silicone CPU. The audience in that movie theater didn't catch why I had burst into laughter  :o

I chose silicone high flex because a) it eases electrode handling and b) it is 200°C rated and won't immediately burst into flames when something unwanted happens.

a 1500W 45A  digital VC and CC controlled power supply  8)
I dream of one of these  ^-^

If that deal is happening then I am seriously looking for some 5 or 6 supercapacitors, I am only not sure how many F's they should have ?  Any link besides Ebay or suggestion is welcome  :)
I have some Maxwell BCAP0310 P270 T10 here, but I haven't found the time to test them yet. Their DC ESR is 2.2 mOhm, I first want to see if that is enough or not, before I can recommend them. I'll keep you updated!

I also see some protection boards with loadbalancing and current limiting, what is that about? Since we do not want current limiting in this application is it safe to use supercapacitors this way or could they also explode as LiPos?
Supercapacitors don't like being overcharged, similar to Lipos. In a similar way, they need balancers when connected in series. For low current applications, that can be a simple resistor, but in our cases we need an active circuit. Typically that is a (e.g. 2.6V) comparator that switches a transistor which connects a resistor in parallel with the cell.

What they like even less is being operated at high temperatures. It is the same as for regular electrolytic capacitors: every 10°C more halves their lifetime.

I haven't heard yet that they can explode, and I have never made this experience. They rather tend to put other things on fire because of their extreme power density  ;)
Title: Re: kWeld - "Next level" DIY battery spot welder
Post by: Kjelt on August 28, 2017, 07:10:29 AM
I chose silicone high flex because a) it eases electrode handling and b) it is 200°C rated and won't immediately burst into flames when something unwanted happens.
Ah yes and you solder that wire to the electrodes that will also need the insulation of the wire to withstand the higher temperature.
Well I found bigger silicone wire (16mm2 upto 120mm2) from HELU or LAPP and othere manufacturers at www.tme.eu (http://www.tme.eu) , a bit pricy but available if needed to lower the resistance even further  8)

Quote
I dream of one of these  ^-^
me too, I so hope that the deal goes through, a dream would come true.
He even has one with 120A  :o  but that one he wants to keep to jumpstart his wifes car, he says he puts it at 16V and can start the car without battery just on that one power supply.
A bit rediculous because the listprice of these supplies are >5k€ but he has gotten them cheap so yeah if he has a practical use for it who am I to judge but I know some people that read this will burst in tears.

Quote
I have some Maxwell BCAP0310 P270 T10 here,I'll keep you updated!
Great! I am looking forward of hearing the experience.

Quote
Supercapacitors don't like being overcharged, similar to Lipos. In a similar way, they need balancers when connected in series. For low current applications, that can be a simple resistor, but in our cases we need an active circuit. Typically that is a (e.g. 2.6V) comparator that switches a transistor which connects a resistor in parallel with the cell.
If I get this correctly if you have 4 supercaps in series and charge it with a controlled Voltage of 10V, still one of the caps might get more than 2.6V due to imbalances in the capacitors?
Than a balancer circuit is also on the shopping list  ;)
Title: Re: kWeld - "Next level" DIY battery spot welder
Post by: ozwolf on August 28, 2017, 09:07:20 AM
G'day,

I've been watching this for a while now.  I had a look at your shop and find "out of stock".

Any plans to assemble more kits?

Ozwolf
Title: Re: kWeld - "Next level" DIY battery spot welder
Post by: tatus1969 on August 28, 2017, 03:10:57 PM
G'day,

I've been watching this for a while now.  I had a look at your shop and find "out of stock".

Any plans to assemble more kits?

Ozwolf
I will definitely make new kits after having received feedback on this first batch, and eventually having included the one or other improvement or feature.
Title: Re: kWeld - "Next level" DIY battery spot welder
Post by: tatus1969 on August 28, 2017, 06:11:30 PM
Ah yes and you solder that wire to the electrodes that will also need the insulation of the wire to withstand the higher temperature.
The electrodes receive a fraction of the heat that is generated at the weld spot, I don't see that we can do anything against this. When welding at higher energies like 100J, they, the electrode holder, and the connecting cable will indeed get quite hot. I alreday have this on my improvement list, because I think that some form of cooling and/or a better heat insulation for your hands is advisable.

available if needed to lower the resistance even further
Be careful when further lowering the resistance. In this application you are basically short circuiting a battery, and there is nothing except battery ESR and the cabling that limits the current. (The power switch is negligible with <0.2mOhm) The welder will go into overcurrent as soon as 2kA is exceeded. And I haven't done robustness testing at this current level yet, only at 1.5kA. The stored inductive energy will almost double from that (E = L * I^2 / 2).

jumpstart his wifes car ... some people that read this will burst in tears.
|O :palm:

If I get this correctly if you have 4 supercaps in series and charge it with a controlled Voltage of 10V, still one of the caps might get more than 2.6V due to imbalances in the capacitors?
Exactly. There are two contributing factors to this. a) of course the capacity variation between them, b) variations in leakage current that causes them to self discharge.
Title: Re: kWeld - "Next level" DIY battery spot welder
Post by: Kjelt on August 28, 2017, 06:19:22 PM
Thanks for the info I have to dig somewhat deeper in that balancing circuit because 4 or 5 caps are in series you can only charge them with the 40Amps when there is no or little resistance between them, if a balancing circuit uses a fet to switch a resistor across one capacitor the resistor should be very low ohms not to influence the charge current ?
If the resistor is too low it drains the charged capacitor, so not sure how this exactly works then. But that is offtopic so probably open another topic about that  :)
Title: Re: kWeld - "Next level" DIY battery spot welder
Post by: tatus1969 on August 28, 2017, 06:30:24 PM
Thanks for the info I have to dig somewhat deeper in that balancing circuit because 4 or 5 caps are in series you can only charge them with the 40Amps when there is no or little resistance between them, if a balancing circuit uses a fet to switch a resistor across one capacitor the resistor should be very low ohms not to influence the charge current ?
If the resistor is too low it drains the charged capacitor, so not sure how this exactly works then. But that is offtopic so probably open another topic about that  :)
I don't understand that current limit? Is that maybe the current carrying capability of the balancer's PCB track that connects the cells? We need special treatment for them in this case anyway, because they will probably immediately melt in this application. A few strips of solder wick will solve that.

The FET / resistor combination is in parallel to the cell, so it does not influence regular charging. It's only purpose is to reduce charging current when the cell voltage gets too high. For example, if we want to charge the cells to 2.6V, then the balancer can kick in at just this voltage and make sure that the steady state voltage will not exceed this. It does not need to hurry here, and it can "work" with the remaining 0.1V.

Additionally, the balancer should have a beefy shottky diode in series with another resistor to remove any possible negative charge. This can always happen when deeply discharging them.
Title: Re: kWeld - "Next level" DIY battery spot welder
Post by: Kjelt on August 28, 2017, 07:04:35 PM
Ah yes I understand now, I am a kind of person that likes to see it (in a schematic)  :)
Ofcourse the normal charge "chain" is not broken so there is still current flowing through the capacitors. Thanks  :-+
Title: Re: kWeld - "Next level" DIY battery spot welder
Post by: tatus1969 on August 28, 2017, 09:28:00 PM
The other capacitor option that I want to investigate, has arrived: 30x 100F far east cheapo capacitors (http://www.ebay.de/itm/263097739655 (http://www.ebay.de/itm/263097739655)). I almost would have bet that they are fake or at least overrated, but I measured 113F capacitance and 13mOhm ESR per cell. Not too bad!

But for now I have to concentrate on the user manual...  ???
Title: Re: kWeld - "Next level" DIY battery spot welder
Post by: SvanGool on August 28, 2017, 09:33:23 PM
Quote
13mOhm ESR per cell. Not too bad!

Don't forget that the ESR multiplies with the number of cells, so you are going to get app. max 200 Amps @ 13 mOhm.
Title: Re: kWeld - "Next level" DIY battery spot welder
Post by: Kjelt on August 28, 2017, 10:24:26 PM
Quote
13mOhm ESR per cell. Not too bad!

Don't forget that the ESR multiplies with the number of cells, so you are going to get app. max 200 Amps @ 13 mOhm.
per string, so five strings would be 1000 Amps.  8)
Title: Re: kWeld - &quot;Next level&quot; DIY battery spot welder
Post by: anishkgt on August 28, 2017, 10:26:10 PM
Yea close to an MOT. Out of curiosity how much max amps does the exiting give out ?


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Title: Re: kWeld - "Next level" DIY battery spot welder
Post by: tatus1969 on August 28, 2017, 10:58:08 PM
Quote
13mOhm ESR per cell. Not too bad!

Don't forget that the ESR multiplies with the number of cells, so you are going to get app. max 200 Amps @ 13 mOhm.
don't forget that the voltage also multiplies. So if one cell delivers 2.7/0.013 = 207A, then six in series will also do that. And I have five strings available that I can parallel.
Title: Re: kWeld - &quot;Next level&quot; DIY battery spot welder
Post by: tatus1969 on August 28, 2017, 11:05:20 PM
Yea close to an MOT. Out of curiosity how much max amps does the exiting give out ?
You mean the welder plus the current Lipo? That is around 1500A. I'm not sure if an MOT delivers that?
Title: Re: kWeld - "Next level" DIY battery spot welder
Post by: SvanGool on August 28, 2017, 11:15:37 PM
Quote
13mOhm ESR per cell. Not too bad!

Don't forget that the ESR multiplies with the number of cells, so you are going to get app. max 200 Amps @ 13 mOhm.
don't forget that the voltage also multiplies. So if one cell delivers 2.7/0.013 = 207A, then six in series will also do that. And I have five strings available that I can parallel.

That is what I said, but I didn't realize you were planning on using all the caps (5 strings) for one welder.  :)
Title: Re: kWeld - "Next level" DIY battery spot welder
Post by: tatus1969 on August 28, 2017, 11:16:43 PM
Quote
13mOhm ESR per cell. Not too bad!

Don't forget that the ESR multiplies with the number of cells, so you are going to get app. max 200 Amps @ 13 mOhm.
don't forget that the voltage also multiplies. So if one cell delivers 2.7/0.013 = 207A, then six in series will also do that. And I have five strings available that I can parallel.

That is what I said, but I didn't realize you were planning on using all the caps (5 strings) for one welder.  :)
ok, got it  :)
Title: Re: kWeld - &quot;Next level&quot; DIY battery spot welder
Post by: anishkgt on August 28, 2017, 11:51:32 PM
Yea close to an MOT. Out of curiosity how much max amps does the exiting give out ?
You mean the welder plus the current Lipo? That is around 1500A. I'm not sure if an MOT delivers that?
Yea MOT (microwave oven transformer) delivers much more than that close 1800A. That is of course after rewinding the secondary with 2AWG copper wire.


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Title: Re: kWeld - "Next level" DIY battery spot welder
Post by: SirJMD on August 29, 2017, 06:53:24 AM
A rewired MOT could be a good power source. I don't know how AC will affect the weld though.

I've ordered a 5000mAh Lipo and some various stuff. Will see how this works and continue from there.
Title: Re: kWeld - &quot;Next level&quot; DIY battery spot welder
Post by: anishkgt on August 29, 2017, 07:41:07 AM
Using a MOT would not fit the purpose of the K-weld because can be very bulky and heavy. On the other hand it can deliver enormous amperes after rectification and proper rewiring.


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Title: Re: kWeld - "Next level" DIY battery spot welder
Post by: Kjelt on August 29, 2017, 07:44:10 AM
Well the six supercaps and supply will also be beefy as well as a car battery.

BTW received the kWeld today looks very nice  :-+ and will start this weekend.
Also the psu deal is going through although the specs are different it is a 3kW psu 0-45V 0-70A  8)
But it has some small issues so I also need to do some TLC there.
Title: Re: kWeld - &quot;Next level&quot; DIY battery spot welder
Post by: SirJMD on August 29, 2017, 05:52:18 PM
Using a MOT would not fit the purpose of the K-weld because can be very bulky and heavy. On the other hand it can deliver enormous amperes after rectification and proper rewiring.


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The purpose is exactly what the user want it to be. If I want a stationary battery welder, then I don't care about size or weight. If you want a small portable welder, that's your choice :)

I like the kWeld so far because of the build quality and functionality. Now I just need to find a good and realiable power source. I'm a bit worried that the continued hammering of the lipo packs might be asking for trouble.
Title: Re: kWeld - &quot;Next level&quot; DIY battery spot welder
Post by: anishkgt on August 29, 2017, 06:06:10 PM
Then the MOT would be a good choice here as a power source.


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Title: Re: kWeld - &quot;Next level&quot; DIY battery spot welder
Post by: tatus1969 on August 29, 2017, 06:27:43 PM
Then the MOT would be a good choice here as a power source.
We would also need a bridge rectifier that can handle these currents, as the kWeld can only switch DC currents.
Title: Re: kWeld - &quot;Next level&quot; DIY battery spot welder
Post by: anishkgt on August 29, 2017, 06:30:56 PM
Yes that would be a enormous one to get the job done. Tatus1969 if you remember I had published a video on my channel showing a pcb for spot welding using a MOT https://youtu.be/WAoY9HTdF6o


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Title: Re: kWeld - "Next level" DIY battery spot welder
Post by: tatus1969 on August 29, 2017, 06:33:24 PM
the psu deal is going through although the specs are different it is a 3kW psu 0-45V 0-70A  8)
:-DD

But it has some small issues so I also need to do some TLC there.
I'm not a native English speaker and wonder what that abbreviation stands for? :)
Title: Re: kWeld - "Next level" DIY battery spot welder
Post by: tautech on August 29, 2017, 07:13:22 PM
But it has some small issues so I also need to do some TLC there.
I'm not a native English speaker and wonder what that abbreviation stands for? :)
Tender Love and Care.  ;)
Title: Re: kWeld - "Next level" DIY battery spot welder
Post by: tatus1969 on August 29, 2017, 07:24:49 PM
But it has some small issues so I also need to do some TLC there.
I'm not a native English speaker and wonder what that abbreviation stands for? :)
Tender Love and Care.  ;)
Thanks  :-+ :-+ :-+
Title: Re: kWeld - &quot;Next level&quot; DIY battery spot welder
Post by: tatus1969 on August 29, 2017, 07:28:28 PM
Yes that would be a enormous one to get the job done. Tatus1969 if you remember I had published a video on my channel showing a pcb for spot welding using a MOT
Yes I had watched that video. You are switching the MOT with an SCR on the primary, that is a common approach. This way you can chop the weld pulse into multiples of 10 milliseconds. I didn't go for that because I wanted a welder that has full and fine control over the pulse time, and the idea of maintaining constant pulse energy cannot be realized with MOT/SCR in my opinion. Therefore I went for the harder way - DC supply and MOSFET switch.
Title: Re: kWeld - &quot;Next level&quot; DIY battery spot welder
Post by: anishkgt on August 29, 2017, 07:31:36 PM
I actually meant to show the size of the MOT and you could use it as power source for the kweld to charge the caps.

The secondary wiring should be thinner to get the desired voltage and thick enough to get the desired amperes.


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Title: Re: kWeld - &quot;Next level&quot; DIY battery spot welder
Post by: tatus1969 on August 29, 2017, 07:41:26 PM
I actually meant to show the size of the MOT and you could use it as power source for the kweld to charge the caps.

The secondary wiring should be thinner to get the desired voltage and thick enough to get the desired amperes.


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Ah, great, I didn't realize that idea. Okay, that means that you use the MOT to make up a decent power supply. You'd also need a high power current limiting voltage regulator then, preferably a buck converter. Or would you try to see how much current the MOT delivers, and just let if flow? Or, at a second thought, we could use primary side phase angle control to set the current.
Title: Re: kWeld - &quot;Next level&quot; DIY battery spot welder
Post by: anishkgt on August 29, 2017, 07:56:49 PM
What is your desired voltage and current ? Since your using a lipo I am guessing it would be 12v and mayb 700A ? A 20 turns of 20 AWG silicone wire would give the desired voltage and amp. The turn is just a guess, you may have to increase or decrease it as needed.


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Title: Re: kWeld - &quot;Next level&quot; DIY battery spot welder
Post by: SirJMD on August 29, 2017, 08:36:37 PM
I actually meant to show the size of the MOT and you could use it as power source for the kweld to charge the caps.

The secondary wiring should be thinner to get the desired voltage and thick enough to get the desired amperes.


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Ah, great, I didn't realize that idea. Okay, that means that you use the MOT to make up a decent power supply. You'd also need a high power current limiting voltage regulator then, preferably a buck converter. Or would you try to see how much current the MOT delivers, and just let if flow? Or, at a second thought, we could use primary side phase angle control to set the current.

I would just "let it flow".

I did a quick look for a rectifier bridge and found one capable of 1.8 kA surge for ~45 euro. I haven't checked the datasheet but it might be suitable.
Title: Re: kWeld - &quot;Next level&quot; DIY battery spot welder
Post by: tatus1969 on August 29, 2017, 10:48:39 PM
What is your desired voltage and current ? Since your using a lipo I am guessing it would be 12v and mayb 700A ? A 20 turns of 20 AWG silicone wire would give the desired voltage and amp. The turn is just a guess, you may have to increase or decrease it as needed.


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Desired voltage is 12V if you want to run kWeld directly from your main supply. You can also use lower voltages, but then you need provide an additional 12V supply for the logic. The current should be between 1kA and 1.5kA. Lower currents are also possible, but that will limit the welding capabilities.
Title: kWeld - "Next level" DIY battery spot welder
Post by: anishkgt on August 29, 2017, 10:50:55 PM
Oh well then the MOT would be a perfect fit for 1kA and 2AWG wire with 3 windings at the secondary and then filtering and rectification follows.

A secondary supply to power the pcb.



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Title: Re: kWeld - &quot;Next level&quot; DIY battery spot welder
Post by: Kjelt on August 30, 2017, 12:00:48 AM
The current should be between 1kA and 1.5kA.
The main fuse was 300A I believe but can withstand these currents for short peaks or how is that designed?
Title: Re: kWeld - &quot;Next level&quot; DIY battery spot welder
Post by: tatus1969 on August 30, 2017, 12:12:12 AM
The current should be between 1kA and 1.5kA.
The main fuse was 300A I believe but can withstand these currents for short peaks or how is that designed?
The time-current curve of the used fuse shows 1 second max at 1kA, which would translate to 0.25 seconds at 2kA. The hardware-limited maximum pulse duration is 0.2 seconds. The fuse will certainly not survive 2kA / 200ms pulses with high repetition rates, but the rest of the system would neither. During my 1.5kA torture / battery discharge test with the new Turnigy nanotech, I continuously monitored several temperatures, and the fuse was by far not the limiting factor - less than 50°C.
Title: Re: kWeld - "Next level" DIY battery spot welder
Post by: Kjelt on August 30, 2017, 12:31:56 AM
Ok thanks clear!
Colleague sent this, no supercaps or batteries required :-DD
https://www.telonic.co.uk/Lab-Power-LAB-DCH20-1500-p/lab-dch20-1500.htm (https://www.telonic.co.uk/Lab-Power-LAB-DCH20-1500-p/lab-dch20-1500.htm)
Title: Re: kWeld - "Next level" DIY battery spot welder
Post by: tatus1969 on August 30, 2017, 12:53:29 AM
Ok thanks clear!
Colleague sent this, no supercaps or batteries required :-DD
https://www.telonic.co.uk/Lab-Power-LAB-DCH20-1500-p/lab-dch20-1500.htm (https://www.telonic.co.uk/Lab-Power-LAB-DCH20-1500-p/lab-dch20-1500.htm)
if that is an option for anyone, then I guess I'll have to rethink the price of my welder :-DD
Title: Re: kWeld - "Next level" DIY battery spot welder
Post by: SvanGool on August 30, 2017, 05:08:52 AM
I have some Maxwell BCAP0310 P270 T10 here, but I haven't found the time to test them yet. Their DC ESR is 2.2 mOhm, I first want to see if that is enough or not, before I can recommend them. I'll keep you updated!

I tried to make a simulation in LTSpice for your Spotwelder based on capacitors. Requirements:

I first tried your idea of BCAP0310:
(http://homit.nl/EEVblog/screenshot.132.jpg)

The graphs:
(http://homit.nl/EEVblog/screenshot.133.jpg)

Some comments:

The result would be, if no mistakes made :), that with 4xBCAP0310 app. 40 Joule welds can be made with 2 mOhm material in 25 ms. The voltages are on the low side for the circuit so it might be necessary to use a Schottky diode and a larger capacitor on the supply of the electronics.
I also did the simulation for 4x BCAP0650: with increase of the wires to 70cm each, all conditions are met and a 75 Joule pulse is possible in 25 ms.

Edit: I updated the screenshots with the latest versions that match the LTSpice files attached in a later post, some cosmetic changes and corrected the Chrg_Cntrl parameters
Title: Re: kWeld - "Next level" DIY battery spot welder
Post by: SirJMD on August 30, 2017, 06:02:41 AM
Ok thanks clear!
Colleague sent this, no supercaps or batteries required :-DD
https://www.telonic.co.uk/Lab-Power-LAB-DCH20-1500-p/lab-dch20-1500.htm (https://www.telonic.co.uk/Lab-Power-LAB-DCH20-1500-p/lab-dch20-1500.htm)

I think I can top that.. >:D

Might need something to step it down.. 70 Mvar at 132 kV.
(http://peecee.dk/uploads/082017/reactor.jpg)
Title: Re: kWeld - "Next level" DIY battery spot welder
Post by: Kjelt on August 30, 2017, 07:14:38 AM
Cheap capacitors
BCAP0310:
BCAP0650:
Wow very nice simulation thanks :-+
Pricing from Maxwell at Mouser is pretty weird.
The BCAP0310s are affordable at around €10 ex VAT a piece but the 0650 is already €35 then the 3000 is "only" €50. So if the 310s would suffice that would be good news otherwise I will probably get the 3000 or even 3400.
Anybody have seen better (lower) prices for those new supercaps except dubious sources such as Ebay?
Title: Re: kWeld - "Next level" DIY battery spot welder
Post by: SirJMD on August 30, 2017, 03:54:30 PM
I have some Maxwell BCAP0310 P270 T10 here, but I haven't found the time to test them yet. Their DC ESR is 2.2 mOhm, I first want to see if that is enough or not, before I can recommend them. I'll keep you updated!

I tried to make a simulation in LTSpice for your Spotwelder based on capacitors. Requirements:
  • Cheap capacitors
  • Normal capacitor voltage above 10V
  • Around 50 Joule in 20 ms
  • Less than 1500A maximum current for 1-4 mOhm material
  • Short circuit current below 2000A
  • Able to weld 10 consecutive welds in 10 seconds

I first tried your idea of BCAP0310:
http://homit.nl/EEVblog/screenshot.130.jpg (http://homit.nl/EEVblog/screenshot.130.jpg)

The graphs:
http://homit.nl/EEVblog/screenshot.129.jpg (http://homit.nl/EEVblog/screenshot.129.jpg)

Some comments:
  • The circuit "Charge_Cntrl" is an additional MOSfet that sees to it that the power supply is not connected when a pulse is fired.
  • The CC_PSU is one of those $20 12V/54A server supplies that can be adjusted to 10.8V
  • The circuit "Weld_Cntrl" is your electronics
  • Do check the parameters, their might still be a mistake in there

The result would be, if no mistakes made :), that with 4xBCAP0310 app. 40 Joule welds can be made with 2 mOhm material in 25 ms. The voltages are on the low side for the circuit so it might be necessary to use a Schottky diode and a larger capacitor on the supply of the electronics.
I also did the simulation for 4x BCAP0650: with increase of the wires to 70cm each, all conditions are met and a 75 Joule pulse is possible in 25 ms.

Looks promising. Shouldn't it be a CC/CV source for charging the caps?

We most likely need to balance the caps or individually manage their voltage, with something like a BMS. For example charge them individually, like how it's done with lipo packs.
Title: Re: kWeld - "Next level" DIY battery spot welder
Post by: SvanGool on August 30, 2017, 05:45:39 PM
@Tatus1969:
I forgot to include the 300A fuse (which is also for capacitors still a good idea) in the internal resistance parameters, it is estimated to have a DC resistance of 375 uOhm, as far as I can find information about that. But I don't see it back in your resistance estimates either or is it already included in one of the parameters?

@Kjelt:
I also simulated 4x BCAP3000s (which I own myself also), they need at least 2x 1 meter AWG8 to not pass the current limits and are then capable of supplying 100 Joule in 25 ms. So they are real "beasts", but a lot of power is "burned" in the cabling. If a higher voltage than 10.8V is required, this spot-welder would be unsuitable for more than 4x BCAP3000, at this moment, for the currents produced.

@SirJMD:
You are correct, the power supply should be the "CC first then CV" type of power supply, that is also what the circuit is simulating.
I didn't simulate a balancer, that would normally operate in parallel of the capacitors shown. But yes, I would at least recommend a "top balancer"/protection for these capacitors. It would need quite some "MOSFet switching" to be able to charge the capacitors individually, I think the current proposed solution with the CC/CV power supply with one additional MOSFet would be a more practical solution.
Title: Re: kWeld - "Next level" DIY battery spot welder
Post by: tatus1969 on August 30, 2017, 06:35:04 PM
I tried to make a simulation in LTSpice for your Spotwelder based on capacitors.
Thanks a lot for that, I'll check carefully and give feedback. Can you provide the simulation files?

Your idea to take a used server PSU is brilliant. Do you know which models are the most common? It seems that almost every model and brand uses a different output connector.

I forgot to include the 300A fuse (which is also for capacitors still a good idea) in the internal resistance parameters, it is estimated to have a DC resistance of 375 uOhm, as far as I can find information about that. But I don't see it back in your resistance estimates either or is it already included in one of the parameters?
I was busy with the operation manual during the last days, and a precision shunt resistor just arrived. I will use that to provide more accurate figures. I already know that I was off by ~10% with my crude current measurement by using a section of AWG8 as a shunt. The cable resistance appears to be higher than expected.

I also simulated 4x BCAP3000s (which I own myself also), they need at least 2x 1 meter AWG8 to not pass the current limits and are then capable of supplying 100 Joule in 25 ms. So they are real "beasts", but a lot of power is "burned" in the cabling. If a higher voltage than 10.8V is required, this spot-welder would be unsuitable for more than 4x BCAP3000, at this moment, for the currents produced.
I included a section in the operation manual that discusses the inductive kickback situation. As mentioned there, I'll try to find the absolute limit through experiments. For now, I am using an estimation (2J is the energy that the TVS diode can take), and that already suggests that the current needs to be limited further when going to long cable lengths. And it would be wise to control the short circuit current (0Ohm weld spot resistance) to stay on the safe side.
Title: kWeld - "Next level" DIY battery spot welder
Post by: anishkgt on August 30, 2017, 08:08:50 PM
A server psu such as https://www.ebay.com/itm/121957144997 (https://www.ebay.com/itm/121957144997)would help.

I use two of these similar ones to power my lipo charger - iCharger 406DUO


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Equipments: DSO104z, Hakko FX888D
Title: Re: kWeld - "Next level" DIY battery spot welder
Post by: SvanGool on August 30, 2017, 09:09:42 PM
Can you provide the simulation files?
Attached.
I used a standard free LTSpiceIV / LTSpiceXVII (http://www.linear.com/designtools/software/#LTspice) version, without any modification (except for changing the options for "background" colors, enabling grid and increasing line thickness for plots).

I modified the "Charge_Cntrl" pulse-timing, because there was an error in there (increased number of pulses) and I modified that timing to be always fitting, using the CV behavior of the power supply (both modifications are corrected in the screenshots of my earlier post).
Here is a detailed picture showing the charging between the two first welding pulses:

(http://homit.nl/EEVblog/screenshot.134.jpg)


Do you know which models are the most common?
I purchased a second-hand HP DPS-600PB to test, it can be modified to adjust voltage between 8-13.8v.


I was busy with the operation manual during the next days, and a precision shunt resistor just arrived. I will use that to provide more accurate figures. I already know that I was off by ~10% with my crude current measurement by using a section of AWG8 as a shunt. The cable resistance appears to be higher than expected.
I included a section in the operation manual that discusses the inductive kickback situation. As mentioned there, I'll try to find the absolute limit through experiments. For now, I am using an estimation (2J is the energy that the TVS diode can take), and that already suggests that the current needs to be limited further when going to long cable lengths. And it would be wise to control the short circuit current (0Ohm weld spot resistance) to stay on the safe side.
When you have more information about the parameters and inductive kickback, I can adjust the model to have a better match with the real-life behavior  :)


Quote from: anishkgt
A server psu such as https://www.ebay.com/itm/121957144997would (https://www.ebay.com/itm/121957144997would) help.
I use two of these similar ones to power my lipo charger - iCharger 406DUO
Looking at the price, that indeed might be a good candidate, do you know what the CC/CV behavior is and if the voltage is adjustable?
Title: Re: kWeld - &quot;Next level&quot; DIY battery spot welder
Post by: anishkgt on August 30, 2017, 09:18:06 PM
Nope I've not tested it to that extreme.  But I can if one can guide me.


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Title: Re: kWeld - &quot;Next level&quot; DIY battery spot welder
Post by: plazma on August 31, 2017, 05:14:23 AM
I bought some Sony 18650 cells for my RC car. The specs got me thinking if they would be good for this application. Max. 100A per cell for <6s. 35A max. continuous. The model is Sony US18650VTCA. In a 2s10p setup it would give max. 1000A 7.4V.
Title: Re: kWeld - &quot;Next level&quot; DIY battery spot welder
Post by: anishkgt on August 31, 2017, 05:55:21 AM
Oh don't bother 18650 cells. You'd need a lot of them compared to just one lipo.


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Title: Re: kWeld - &quot;Next level&quot; DIY battery spot welder
Post by: plazma on August 31, 2017, 06:35:53 AM
Oh don't bother 18650 cells. You'd need a lot of them compared to just one lipo.


Www.Georgehobby.wordpress.com

Equipments: DSO104z, Hakko FX888D
18650 cells can have very different chemistries and current ratings. Show me a similar volume LiPo with better current rating than the Sony cell.
Title: Re: kWeld - &quot;Next level&quot; DIY battery spot welder
Post by: anishkgt on August 31, 2017, 07:01:11 AM
Well I was talking about the size to capacity ratio. They can have different chemistries but the burst amps is what makes the difference. A lipo is good at it.


Www.Georgehobby.wordpress.com

Equipments: DSO104z, Hakko FX888D
Title: Re: kWeld - &quot;Next level&quot; DIY battery spot welder
Post by: plazma on August 31, 2017, 07:07:28 AM
Looks like my first message got truncated to half. The Sony cell can give 35A continuous and 100A max. for 6s. A 2s10p pack would give 1000A 7.2V max. I also wrote the cell type Sony US18650VTC5A.
Title: Re: kWeld - &quot;Next level&quot; DIY battery spot welder
Post by: SvanGool on August 31, 2017, 10:01:14 AM
Nope I've not tested it to that extreme.  But I can if one can guide me.

You would need a normal large electrolytic capacitor of e.g. 22000uF/16V, like http://www.mouser.com/ProductDetail/Cornell-Dubilier/229TTA016M  (http://www.mouser.com/ProductDetail/Cornell-Dubilier/229TTA016M) and a storage oscilloscope to show you a few milliseconds when you connect the power supply you proposed (rating 12V/100A). Connect the oscilloscope to the capacitor and set it to trigger just above 0V and then connect the power-supply to the capacitor (matching polarity of PSU and cap). Do you use thick wiring between PSU and cap.

The picture on the oscilloscope should look similar to this, when your power supply would operate, as desired, for ultra-capacitor usage:

(http://homit.nl/EEVblog/screenshot.135.jpg)

Title: Re: kWeld - &quot;Next level&quot; DIY battery spot welder
Post by: tatus1969 on August 31, 2017, 06:22:39 PM
Nope I've not tested it to that extreme.  But I can if one can guide me.

You would need a normal large electrolytic capacitor of e.g. 22000uF/16V, like http://www.mouser.com/ProductDetail/Cornell-Dubilier/229TTA016M  (http://www.mouser.com/ProductDetail/Cornell-Dubilier/229TTA016M) and a storage oscilloscope to show you a few milliseconds when you connect the power supply you proposed (rating 12V/100A). Connect the oscilloscope to the capacitor and set it to trigger just above 0V and then connect the power-supply to the capacitor (matching polarity of PSU and cap). Do you use thick wiring between PSU and cap.

The picture on the oscilloscope should look similar to this, when your power supply would operate, as desired, for ultra-capacitor usage:
I would be surprised if they would have a current limiting circuit. I had ordered one 1kW model yesterday and will check that. But they do have remote voltage sensing, and this can eventually be turned into a constant current supply in combination with a beefy measurement shunt and an opamp circuit.
Title: Re: kWeld - "Next level" DIY battery spot welder
Post by: tatus1969 on August 31, 2017, 06:25:10 PM
another question: does anyone know how the matching connectors for these are called, and where they can be ordered? I don't want to solder directly to the PSU.

(https://img.rcgroups.com/http://uploads.tapatalk-cdn.com/20160827/45306669a39da9a17dd7032f4f512433.jpg?h=M6EOt_-5NinT1qn0n0H82w)
Title: Re: kWeld - &quot;Next level&quot; DIY battery spot welder
Post by: anishkgt on August 31, 2017, 06:27:49 PM
Hard to find the connector for that separately as these are attached to the server itself. You will have to solder it that is how I use them. Maybe you could check with supplier or check with any local IT company for any scrap servers that would fit.


Www.Georgehobby.wordpress.com

Equipments: DSO104z, Hakko FX888D
Title: Re: kWeld - "Next level" DIY battery spot welder
Post by: Kjelt on August 31, 2017, 06:40:22 PM
another question: does anyone know how the matching connectors for these are called, and where they can be ordered? I don't want to solder directly to the PSU.
That will be extremely difficult, perhaps you can measure the pitch between the individual traces (you can see the sliding of the connectors) and buy a standard card edge connector of the right width and remove the pins that are not used or might become a short hazzard.
Title: Re: kWeld - "Next level" DIY battery spot welder
Post by: tatus1969 on August 31, 2017, 07:00:52 PM
another question: does anyone know how the matching connectors for these are called, and where they can be ordered? I don't want to solder directly to the PSU.
That will be extremely difficult, perhaps you can measure the pitch between the individual traces (you can see the sliding of the connectors) and buy a standard card edge connector of the right width and remove the pins that are not used or might become a short hazzard.
found them, they are using these: https://www.digikey.de/products/de/connectors-interconnects/card-edge-connectors-edgeboard-connectors/303?k=&pkeyword=&pv69=367&FV=ffe0012f%2C160003f%2C1640001%2C1680002%2C17a8000d%2C1f140000&mnonly=0&ColumnSort=0&page=1&stock=1&quantity=0&ptm=0&fid=0&pageSize=25 (https://www.digikey.de/products/de/connectors-interconnects/card-edge-connectors-edgeboard-connectors/303?k=&pkeyword=&pv69=367&FV=ffe0012f%2C160003f%2C1640001%2C1680002%2C17a8000d%2C1f140000&mnonly=0&ColumnSort=0&page=1&stock=1&quantity=0&ptm=0&fid=0&pageSize=25)

these ones are even better: https://www.digikey.de/product-detail/de/te-connectivity-amp-connectors/1761426-1/A107664-ND/4021545 (https://www.digikey.de/product-detail/de/te-connectivity-amp-connectors/1761426-1/A107664-ND/4021545) [EDIT: these have four positions too many...]
Title: Re: kWeld - &quot;Next level&quot; DIY battery spot welder
Post by: tatus1969 on August 31, 2017, 07:44:01 PM
Looks like my first message got truncated to half. The Sony cell can give 35A continuous and 100A max. for 6s. A 2s10p pack would give 1000A 7.2V max. I also wrote the cell type Sony US18650VTC5A.
I only have incomplete data on these, can you share the information that you have? I didn't know that they should be good for 100A pulse. My experience though is that most Liion cells are optimized for energy density, whereas Lipos are optimized for power density:
US18650VTC5A:                        2.9kW/kg (35A cont, 3.7V, 45g)
Turnigy nanotech 3S/5Ah/130C: 8.1kW/kg (325A cont, 11.1V, 442g)

Afaik, Lipos can currently only be beaten by supercapacitors.
Title: Re: kWeld - &quot;Next level&quot; DIY battery spot welder
Post by: SirJMD on August 31, 2017, 07:54:00 PM
I bought some Sony 18650 cells for my RC car. The specs got me thinking if they would be good for this application. Max. 100A per cell for <6s. 35A max. continuous. The model is Sony US18650VTCA. In a 2s10p setup it would give max. 1000A 7.4V.

100A from a 18650 sounds a bit too high. It's around 40C - many Lipo packs can't even handle that. I couldn't find the datasheet for the model you mentioned, but for US18650VTC5 the maximum discharge seems to be around 20A, or around 8C.
Title: Re: kWeld - &quot;Next level&quot; DIY battery spot welder
Post by: plazma on August 31, 2017, 07:57:19 PM
All specs are better with that LiPo. Internal impedance is very low.
Title: Re: kWeld - &quot;Next level&quot; DIY battery spot welder
Post by: SirJMD on August 31, 2017, 08:11:41 PM
Looks like my first message got truncated to half. The Sony cell can give 35A continuous and 100A max. for 6s. A 2s10p pack would give 1000A 7.2V max. I also wrote the cell type Sony US18650VTC5A.
I only have incomplete data on these, can you share the information that you have? I didn't know that they should be good for 100A pulse. My experience though is that most Liion cells are optimized for energy density, whereas Lipos are optimized for power density:
US18650VTC5A:                        2.9kW/kg (35A cont, 3.7V, 45g)
Turnigy nanotech 3S/5Ah/130C: 8.1kW/kg (325A cont, 11.1V, 442g)

Afaik, Lipos can currently only be beaten by supercapacitors.

I would be cautious about drawing that high current form li-ion cells. "Fun" things start to happen when the cells get hot.

Good quality 18650 cells can be a bit pricy, so in that regard I think the supercaps are the best option so far, if they can take the beating.
But we would have to include a management system for them, to protect against overcharging.
Title: Re: kWeld - "Next level" DIY battery spot welder
Post by: SvanGool on August 31, 2017, 08:13:29 PM
Found them, they are using these: https://www.digikey.de/products/de/connectors-interconnects/card-edge-connectors-edgeboard-connectors/303?k=&pkeyword=&pv69=367&FV=ffe0012f%2C160003f%2C1640001%2C1680002%2C17a8000d%2C1f140000&mnonly=0&ColumnSort=0&page=1&stock=1&quantity=0&ptm=0&fid=0&pageSize=25 (https://www.digikey.de/products/de/connectors-interconnects/card-edge-connectors-edgeboard-connectors/303?k=&pkeyword=&pv69=367&FV=ffe0012f%2C160003f%2C1640001%2C1680002%2C17a8000d%2C1f140000&mnonly=0&ColumnSort=0&page=1&stock=1&quantity=0&ptm=0&fid=0&pageSize=25)

these ones are even better: https://www.digikey.de/product-detail/de/te-connectivity-amp-connectors/1761426-1/A107664-ND/4021545 (https://www.digikey.de/product-detail/de/te-connectivity-amp-connectors/1761426-1/A107664-ND/4021545) [EDIT: these have four positions too many...]

Be aware that the TE Standard Edge II card edge connectors have a contact rating of 3A  ???
I would take a look at TE "Crown edge" or "SEC-II".
Title: Re: kWeld - "Next level" DIY battery spot welder
Post by: tatus1969 on August 31, 2017, 09:29:06 PM
Found them, they are using these: https://www.digikey.de/products/de/connectors-interconnects/card-edge-connectors-edgeboard-connectors/303?k=&pkeyword=&pv69=367&FV=ffe0012f%2C160003f%2C1640001%2C1680002%2C17a8000d%2C1f140000&mnonly=0&ColumnSort=0&page=1&stock=1&quantity=0&ptm=0&fid=0&pageSize=25 (https://www.digikey.de/products/de/connectors-interconnects/card-edge-connectors-edgeboard-connectors/303?k=&pkeyword=&pv69=367&FV=ffe0012f%2C160003f%2C1640001%2C1680002%2C17a8000d%2C1f140000&mnonly=0&ColumnSort=0&page=1&stock=1&quantity=0&ptm=0&fid=0&pageSize=25)

these ones are even better: https://www.digikey.de/product-detail/de/te-connectivity-amp-connectors/1761426-1/A107664-ND/4021545 (https://www.digikey.de/product-detail/de/te-connectivity-amp-connectors/1761426-1/A107664-ND/4021545) [EDIT: these have four positions too many...]

Be aware that the TE Standard Edge II card edge connectors have a contact rating of 3A  ???
I would take a look at TE "Crown edge" or "SEC-II".
There are 24 of them in parallel per pole, if load sharing works reasonably well then I am not too concerned.
Title: Re: kWeld - "Next level" DIY battery spot welder
Post by: tatus1969 on August 31, 2017, 11:08:15 PM
I have data from a calibrated measurement (3% current accuracy, 3% voltage accuracy):

Setup:         
- kWeld current measurement calibrated with 0.5% shunt resistor         
- probes shorted as shown right (20mm open between holders)         
         
V   A   milliOhms   Where measured
2.72   1452   1.87   Probe system, measured between top of terminal screws
0.472   1451   0.33   Power switch, measured between terminal screws
1.12   1441   0.78   Fuse, measaured between terminal screws
0.272   1441   0.19   Battery plus cable, measured between terminal screw and cable end
0.272   1441   0.19   Battery minus cable, measured between terminal screw and cable end
4.88   1460   3.34   Total system resistance, measured between kWeld cable ends

Title: Re: kWeld - &quot;Next level&quot; DIY battery spot welder
Post by: tatus1969 on September 01, 2017, 03:16:35 AM
But they do have remote voltage sensing, and this can eventually be turned into a constant current supply in combination with a beefy measurement shunt and an opamp circuit.
just found this thread https://endless-sphere.com/forums/viewtopic.php?f=14&t=47415 :-)
Title: Re: kWeld - &quot;Next level&quot; DIY battery spot welder
Post by: SvanGool on September 01, 2017, 06:44:30 AM
But they do have remote voltage sensing, and this can eventually be turned into a constant current supply in combination with a beefy measurement shunt and an opamp circuit.
just found this thread https://endless-sphere.com/forums/viewtopic.php?f=14&t=47415 :-)
I have two DPS-600PB on the way. They can be put in parallel (load sharing) and decreased to 10.8V (which I could not find for other PSUs) for app. 80A. I think I also found a way to solve the potential cc/cv problem by putting a couple of parallel 12V/200W halogen lamps in series between PSUs and caps. Those lamps have a much higher resistance when they are on, which should be enough to start the PSUs.

The mod in the thread you found, only works from 8V up but the supercaps charger should be able to work from 0V up. Maybe a combination is possible by short-circuiting the lamps, by an additional MOSfet, when the voltage reaches 8V. But this is all (or partially) only necessary, when the PSU really switches off, when loaded by a plain supercap bank, let's first test when the goodies arrive :)

Edit: added last paragraph.

Title: Re: kWeld - "Next level" DIY battery spot welder
Post by: SirJMD on September 01, 2017, 05:53:23 PM
And so it begins..!

(http://peecee.dk/uploads/092017/soitbegins.jpg)
Title: Re: kWeld - "Next level" DIY battery spot welder
Post by: tatus1969 on September 02, 2017, 02:01:52 AM
I've got some first results from using Maxwell capacitors. Four of them are enough for 90 joules into a 1 milliohm weld spot. My requirement was 100 joules, and that is not reached yet.

But their ESR is surprisingly low, I measured only 1.5 milliohms per cell, in contrast to the 2.2 milliohm in the datasheet.

(http://www.eevblog.com/forum/projects/guesses-on-what-i-am-attempting-here/?action=dlattach;attach=346859)

Title: Re: kWeld - "Next level" DIY battery spot welder
Post by: Kjelt on September 02, 2017, 03:40:50 AM
Does that mean you need five supercaps or is the voltage then too high?

I am doing the crimp on the cables at the moment, first time I used the hydraulic Amp tool from 1983 i inherited from a friend.
But I find the AWG8 cables a bit thin and 1m too short for my electrode holder that needs to move up and down. So just thinking what about car starter / booster cables. They are available in 500A (25mm2), 700A (35mm2) even 1000A (50mm2) and have fully isolated crocodile clamps that can easily be attached to the supercaps and/or powersupply.

Any thoughts?
Title: Re: kWeld - "Next level" DIY battery spot welder
Post by: SirJMD on September 02, 2017, 04:33:20 AM
I've started testing the kWeld - with sparks going everywhere.

At 50J I burned straight through the nickel strips. At 14.6J I get strong welds but still sparks going everywhere, even though I press down on the electrodes rather hard. Peak current was just over 1400A.

14.6J
6,74ms
1.03 mOhm
1428A

With the calibration it set an offset of 66 and a resistance of 1.95 mOhm.
Title: Re: kWeld - "Next level" DIY battery spot welder
Post by: SirJMD on September 02, 2017, 07:36:14 PM
I've done some more testing and it feels like it shoots much more juice than the setting says.

At just 5 joule I get strong welds where the tabs can only be removed with pliers, with the tabs being ripped apart. At 50 joule it becomes a handheld arc welder.
Title: Re: kWeld - "Next level" DIY battery spot welder
Post by: tatus1969 on September 02, 2017, 08:19:27 PM
I've started testing the kWeld - with sparks going everywhere.

At 50J I burned straight through the nickel strips. At 14.6J I get strong welds but still sparks going everywhere, even though I press down on the electrodes rather hard. Peak current was just over 1400A.

14.6J
6,74ms
1.03 mOhm
1428A

With the calibration it set an offset of 66 and a resistance of 1.95 mOhm.
What kind of nickel strip do you have, is it 0.1mm? And is it maybe nickel plated steel? (You can test it with a Dremel with cutting disc, if it is pure nickel then you won't see any sparks.)

The numbers are consistent though, as 1428^2 * 1.03e-3 * 6.74e-3 = 14.15J. Current and weld spot resistance are also typical, and if you can verify the pulse time for correctness then I think that the system works as it should.

Does that mean you need five supercaps or is the voltage then too high?
No, the voltage is 10.5V now, which is barely enough for the kWeld to be used without an auxiliary logic supply. I want to use as few capacitors as possible to find the optimum price/performance point. These are 10€ each, and everyone counts :-) I don't consider throwing parts on a problem as good engineering. The kWeld power switch will also receive a detailed evaluation in which I will reduce the number of transistors, and at the same time bring the current to its limits. I tried to simulate these things, but it is difficulty to find a realistic model especially for the inductive kickback. Just modeling the current sharing between diode and MOSFETs is almost impossible, the existing models are not accurate at these current levels.

I am doing the crimp on the cables at the moment, first time I used the hydraulic Amp tool from 1983 i inherited from a friend.
Great  :-+

But I find the AWG8 cables a bit thin and 1m too short for my electrode holder that needs to move up and down. So just thinking what about car starter / booster cables. They are available in 500A (25mm2), 700A (35mm2) even 1000A (50mm2) and have fully isolated crocodile clamps that can easily be attached to the supercaps and/or powersupply.
Have you found time to read the operation manual? I am discussing this topic there. You need to find a tradeoff between cable length and ohmic resistance. There are two limits that may not be exceeded: maximum current, and maximum inductive kickback energy.

The system basically short-circuits a capable power supply, and all that's in the way is the loop resistance. I don't remember how are you going to supply the system?

Edit: just took this picture. kneel down at this beautiful piece of art. The two transformers are just 20x25x25mm each, there are only five output caps, the entire power stage (except PFC and input capacitors) is just 70x60x35mm, and it's rated for 12V / 82A.

(http://www.eevblog.com/forum/projects/guesses-on-what-i-am-attempting-here/?action=dlattach;attach=347180)
Title: Re: kWeld - "Next level" DIY battery spot welder
Post by: Fraser on September 02, 2017, 09:14:46 PM
I purchased a Turnigy 5000mAh LiPo pack this week. I also purchased the pretty much essential Turnigy fire containment bag in which the LiPo will live.

For me, I thought it would be nice to have the large 15Ah or 36Ah Pb Gel 12V battery for static use in the lab, but also to have the option for more mobile use using the LiPo battery option. Occasional use will hopefully not stress it too much.
O
Whilst I understand the desire to develop this welder to meet many different needs, I would like to avoid the situation lampooned with early LED digital watches in many cartoons...... that is to say, the nice compact watch on your wrist and the huge power source pulled along behind you on a cart !  In my world, small is beautiful :) The super capacitors seem pretty compact these days but it appears the demands for charging them quickly lead to a quite bulky power supply. Batteries charge more slowly so no need for a large PSU, yet they have large capacity to keep delivering current pulses via the kWeld before needing a recharge. In 'amateur' use this seems desirable.

Fraser

The kWeld is a very neat and compact welder solution that can operate away from utility mains. This is wonderful for portable use away from the lab, or just where you do not want a bulky mains power supply.

IMHO, the beauty of the kWeld design is that it is a well formed 'welding core' , a bit like the thermal imaging 'core' format with which I am more familiar. It may be integrated into a welding system that suits each user. A superb option for those of us who wish to customise and experiment :)

Good luck with the development of the supercapacitor solution, I hope that it provides decent performance whilst not making the welder unwieldy or oversize. It is great to read of your experimentation though as I have no practical knowledge of the modern supercapacitors being discussed here.

If it is not too rude a question, why are people so keen to use the supercapacitors instead of battery power sources ? Lower ESR ? Higher current tolerance ? , it certainly isn't low cost :)

Best Wishes to all my fellow kWeld owners and especially to Frank, the father of the kWeld  :-+
Title: Re: kWeld - "Next level" DIY battery spot welder
Post by: Kjelt on September 02, 2017, 10:03:51 PM
But I find the AWG8 cables a bit thin and 1m too short for my electrode holder that needs to move up and down. So just thinking what about car starter / booster cables. They are available in 500A (25mm2), 700A (35mm2) even 1000A (50mm2) and have fully isolated crocodile clamps that can easily be attached to the supercaps and/or powersupply.
Have you found time to read the operation manual? I am discussing this topic there. You need to find a tradeoff between cable length and ohmic resistance. There are two limits that may not be exceeded: maximum current, and maximum inductive kickback energy.
The system basically short-circuits a capable power supply, and all that's in the way is the loop resistance. I don't remember how are you going to supply the system?
Ah ok clear I thought it was about the output cables.
It is hard for me to measure such low resistances even with a 4 wire multimeter.

What I intend to do now is to use the 1meter 8awg you supplied only for the output wiring (2x50cm) to the electrodes and use a 16mm2 cables from a carstartercable set I just bought to the input with clamps attached. That way I can power the kWeld with a carbattery or supercaps or whatever by just clamping it up instead of using connectors.

At the moment I have no powersource which can provide 1500A.
The labsupply is "only" 70Amps and needs more rework than thought (it was rewired by the previous owner to get out of spec) so that will be something I am going to do the coming week.

I am awaiting the trials and errors you are conducting to buy the correct number and type of supercapacitors.
I do have a small leadbattery I could use for just testing if the kWeld works but that will not suplly enough current just a test to see the system powers up and works. I could also use the powersupply as it is now and test it (it will short the caps of the supply and not have enough current but for a test I know that everything works).

Last but not least the kWeld gets a standard boxhousing with transparent lid but mechanical work will also take time.


Title: Re: kWeld - "Next level" DIY battery spot welder
Post by: Fraser on September 02, 2017, 10:25:44 PM
I bought a couple of LiPo cell monitors and balancing units for my kWeld battery. They are cheap but effective for keeping an eye on the state of the LiPo before, during and after use  :) Useful little gadgets.

One has a large display and several useful functions whilst the other has fewer functions but shows all cell voltages on the same screen for easy monitoring. The cell balancer is also a useful facility to have.

I recommend one of these for those users electing to operate from a LiPo battery pack as they have a low voltage warning alarm that may be set to your needs per cell. There are plenty available on eBay.

Fraser
Title: Re: kWeld - "Next level" DIY battery spot welder
Post by: anishkgt on September 03, 2017, 12:00:30 AM
 and these are more common.

http://www.ebay.com/itm/RC-Lipo-Battery-Low-Voltage-Alarm-1S-8S-Buzzer-Indicator-Checker-Tester-LED-Best-/282397825614?hash=item41c038da4e:g:7bUAAOSw14xWKh-Q (http://www.ebay.com/itm/RC-Lipo-Battery-Low-Voltage-Alarm-1S-8S-Buzzer-Indicator-Checker-Tester-LED-Best-/282397825614?hash=item41c038da4e:g:7bUAAOSw14xWKh-Q)
Small and has an audible alert when a desired voltage has occurred. The buzzers can be replaced with a relay and wire it up to cut-off the load when the pre set voltage has reached.
Title: Re: kWeld - "Next level" DIY battery spot welder
Post by: Fraser on September 03, 2017, 12:16:22 AM
Indeed, there are many versions around and most are very cheap.

When effectively abusing a 3S LiPo battery it seems a very good idea to keep an eye on its cell balance and general health :)

My only concern with a "cut-out' circuit using one of these is whether the cut-out would trigger during the very high current draw of the welding operation ? You could end up with spurious and annoying 'trips' of the welder.

Fraser
Title: Re: kWeld - "Next level" DIY battery spot welder
Post by: tatus1969 on September 03, 2017, 12:47:27 AM
Wired up 5 x BCAP0310 in series now, and the server PSU also had its first task today.

I didn't mod the PSU's output voltage yet, by default it has 12.5V. Even though this is not enough yet for the capacitors (5x2.7=13.5), this setup can do 110J weld energy into 1mOhm.

(http://www.eevblog.com/forum/projects/guesses-on-what-i-am-attempting-here/?action=dlattach;attach=347232)

I don't have balancers on the capacitors yet, but they already show that they want that.

Next will be stress testing them, in order to see if they can handle this current without damage or overheating. But I think that they will need some forced air cooling.

The PSU is doing very well, I'm impressed. With my setup below, it trickle charges the capacitors because it goes into overcurrent shutdown at ~100A every 25ms. At ~9V, it succeeds to start up, but that is partly because of that high impedance lab wiring. I definitely don't recommend doing this, because I fear that the PSU may die on that the sooner or later.

But the good news is that the PSU has a remote sense input that supposedly allows voltage control from 10.5V to 13.5V, which is spot on for the capacitor bank. The idea is: resistor limited pre-charge up to 10.5V (adjustable). Then using the remote sense input (plus an opamp plus a current shunt resistor) to charge with 70A (adjustable) current. Then keep the capacitor topped at 13.5V (adjustable).

At 70A, the PSU is theoretically able to recharge from a 50J / 1mOhm weld pulse in 0.7 seconds. That should be more than fast enough to be usable.

I'll breadboard this and make capacitor torture testing with that setup...
Title: Re: kWeld - "Next level" DIY battery spot welder
Post by: tatus1969 on September 03, 2017, 01:08:02 AM
If it is not too rude a question, why are people so keen to use the supercapacitors instead of battery power sources ? Lower ESR ? Higher current tolerance ? , it certainly isn't low cost :)
Certainly not a rude question :-) My objective is to provide a stationery alternative to the portable Lipo supply. It should be cost effective, and I think I can even beat the price of the suggested Lipo plus the neccesary charger (at least 100€). The five Maxwell capacitors are 7.74€ per 100 each, the control board may be around 40€. I want to design it specifically for the HP DPS-800GB server PSU, there are lots of used at ebay for around 20€.

Best Wishes to all my fellow kWeld owners and especially to Frank, the father of the kWeld  :-+
Thanks, I go a long with that wish!
Title: Re: kWeld - "Next level" DIY battery spot welder
Post by: SirJMD on September 03, 2017, 03:50:38 AM
I've started testing the kWeld - with sparks going everywhere.

At 50J I burned straight through the nickel strips. At 14.6J I get strong welds but still sparks going everywhere, even though I press down on the electrodes rather hard. Peak current was just over 1400A.

14.6J
6,74ms
1.03 mOhm
1428A

With the calibration it set an offset of 66 and a resistance of 1.95 mOhm.
What kind of nickel strip do you have, is it 0.1mm? And is it maybe nickel plated steel? (You can test it with a Dremel with cutting disc, if it is pure nickel then you won't see any sparks.)

The numbers are consistent though, as 1428^2 * 1.03e-3 * 6.74e-3 = 14.15J. Current and weld spot resistance are also typical, and if you can verify the pulse time for correctness then I think that the system works as it should.

It should be pure nickel, but probably isn't. I bought it long ago on eBay, so it's probably plated steel. Sadly I don't have a Dremel or an angle grinder at hand, to test it with.


What kind of pulse is the kWeld making? Single large pulse?
I know that commercial spot welders utilizes a dual pulse. Would that be possible with the kWeld?
Title: Re: kWeld - "Next level" DIY battery spot welder
Post by: tatus1969 on September 03, 2017, 08:40:34 AM
What kind of pulse is the kWeld making? Single large pulse?
I know that commercial spot welders utilizes a dual pulse. Would that be possible with the kWeld?
kWeld is single pulse - I currently keep my position that it doesn't need double pulse technique, because the implemented energy metering is superior. Of course it is very simple to change the behaviour in the firmware... I'm happily up to the discussion.

EDIT: I think that double pulse is necessary in conventional welders because when pulse time is kept constant, then delivered weld spot energy depends on the weld spot resistance. That can vary when there is bad contact due to corrosion or weak contact force. I made the constant energy approach to get rid of these factors.
Title: Re: kWeld - "Next level" DIY battery spot welder
Post by: 3roomlab on September 03, 2017, 01:31:33 PM
i have been trying to learn some of the background "science" of this nice project by tatus1969 from googling
and here is also a version of LTspice simulation, i added a C2 n some diodes to deal with the kick back which i assume is what was mentioned in 1 of the posts as being a danger? it appears due to the very high current, the simulation seem to say the kick back could go over 1kV? not sure about this but maybe someone else can comment on this.

the cable specs are "stretched" to simulate what if lengths.
the simulation is somewhat fun, its a somewhat "non-destructive" way to find cable parameters that fit a certain current/weld output profile
(the txt file needs to be renamed to *.asc for LTspice)

:P
Title: Re: kWeld - "Next level" DIY battery spot welder
Post by: tatus1969 on September 03, 2017, 05:49:07 PM
i have been trying to learn some of the background "science" of this nice project by tatus1969 from googling
and here is also a version of LTspice simulation, i added a C2 n some diodes to deal with the kick back which i assume is what was mentioned in 1 of the posts as being a danger? it appears due to the very high current, the simulation seem to say the kick back could go over 1kV? not sure about this but maybe someone else can comment on this.

the cable specs are "stretched" to simulate what if lengths.
the simulation is somewhat fun, its a somewhat "non-destructive" way to find cable parameters that fit a certain current/weld output profile
(the txt file needs to be renamed to *.asc for LTspice)

:P
Inductive kickback has no theoretical limit. If you manage to instantaneously interrupt the current in an inductor, then it produces -infinity volts.

The switch and diode are not wired in the same way as in kWeld (not really essential, but it may help in our further discussion if you change this): the power transistors are in the ground return path. You need to add a big 50V zener diode across them, because that's their behavior when given too much voltage (MOSFET avalanche). The TVS diode that is in the system as well goes from the + output lead (=cathode) to the - output lead =(anode). The voltage across the swtich at turn off should look like in the picture (standard 1.0m system lead length + 0.2m on the battery, 1400A current).

EDIT: one more comment: the capacitor across the switch is not a good idea, as it stores charge that is dumped into the switch at turn on. The charge at 10V would be 10^2 * 47m / 2 = 4.7J. This would destroy the power switch.
Title: Re: kWeld - "Next level" DIY battery spot welder
Post by: SirJMD on September 03, 2017, 08:33:40 PM
What kind of pulse is the kWeld making? Single large pulse?
I know that commercial spot welders utilizes a dual pulse. Would that be possible with the kWeld?
kWeld is single pulse - I currently keep my position that it doesn't need double pulse technique, because the implemented energy metering is superior. Of course it is very simple to change the behaviour in the firmware... I'm happily up to the discussion.

EDIT: I think that double pulse is necessary in conventional welders because when pulse time is kept constant, then delivered weld spot energy depends on the weld spot resistance. That can vary when there is bad contact due to corrosion or weak contact force. I made the constant energy approach to get rid of these factors.

I've heard that the first pulse's purpose is to remove oils and other impurities, so the second pulse can perform the actual weld.

I'm by no means an expert in that area, but it sounds plausible. I'm not sure how to test it in practice.
Title: Re: kWeld - "Next level" DIY battery spot welder
Post by: SvanGool on September 03, 2017, 09:15:19 PM
... It trickle charges the capacitors because it goes into overcurrent shutdown at ~100A every 25ms ...

I got halogen 12 V/100 W projection lamps in: they measured 100 mOhm when cold and will be about 1.5 Ohm when normally on.
I assume that if you would put such a lamp in between one supply power lead of your power supply and the capacitors, the power supply would operate normally: at the start the lamp would be turned on at 12 V (caps at 0 Volt) and current at app.8 A, while charging the voltage over the lamp will decrease, the resistance of the lamp will decrease and the current will increase after that. Can't test it myself yet  :)
Title: Re: kWeld - "Next level" DIY battery spot welder
Post by: joddi on September 03, 2017, 09:16:40 PM
I'm curious if I can use this LiTiO (6S):
https://www.ev-power.eu/LTO-technology/Lithium-Titanate-Oxid-Battery-Cell-LTO-2-4V-30AH.html?cur=1 (https://www.ev-power.eu/LTO-technology/Lithium-Titanate-Oxid-Battery-Cell-LTO-2-4V-30AH.html?cur=1)

Price may not be competitive but my idea is:
- use 6S LTO battery pack in my car as a secondary battery (should have good cold temperature performance for cold starts)
- make this battery removable from car and use it as a occassional portable powersource (for kWeld...)
- charging would be done in car from alternator
Title: Re: kWeld - "Next level" DIY battery spot welder
Post by: 3roomlab on September 03, 2017, 10:04:34 PM
The switch and diode are not wired in the same way as in kWeld (not really essential, but it may help in our further discussion if you change this)

ops, this is now re-arranged.
thanks for the correction
now even the short battery lead is making quite a ton of voltage spikes
Title: Re: kWeld - "Next level" DIY battery spot welder
Post by: Kjelt on September 04, 2017, 02:08:36 AM
Removed my post since it was my own stupid mistake. The taps were placed back in different order so I found just out while putting everything back that it was an M6 tap instead of an M5 tap I used.  |O
Since now one piece of the electrode brass pipe is damaged I have to find another way to construct the electrodes.
Title: Re: kWeld - "Next level" DIY battery spot welder
Post by: Fraser on September 04, 2017, 02:29:59 AM
We all make mistakes ! At least you discovered why you were having a problem  :)

I was considering other probe designs myself and one that I was going to investigate was using a pair of the XT-150 (or similar bullet connectors) at the probe tip. The female part would be soldered to the brass tube that is filled with a 4mm copper rod. The welding tip would be made from shaped copper rod that is soldered into the male XT-150 connector. The XT-150 plastic casing would not be used. This would make it easy to change between different welding tip shapes and profiles. For example, straight and 30 degree angled tips, or offset/stepped diameter tips for confined space working. I have lathes so can easily experiment with tip shapes.

The drawback of using the XT-150 connectors for the probe tip mounting may be the connection resistance that it may introduce. They are gold plated and oxidisation resistant though.

Just a thought at the moment as I have no time to play for a while.

Fraser
Title: Re: kWeld - "Next level" DIY battery spot welder
Post by: SeanB on September 04, 2017, 02:35:43 AM
Simple fix there Kjelt is to retap with a recoil tap and put in a M5 insert, which uses almost the same diameter and which will recover most of the diameter and most of the strength. Not as good conductivity wise as it is stainless steel as opposed to brass, but so long as tyhe ends which are good conductors are in good electric contact it will work well enough just with slightly higher resistance.

Been there done the same, and did a similar fix.
Title: Re: kWeld - "Next level" DIY battery spot welder
Post by: Fraser on September 04, 2017, 03:08:14 AM
Something else to consider. The brass tube does not need to be very long as it is just a coupler. You need just enough length for the crimped section and a short threaded section for the tip mounting. You can insert the 'coupler' into a nice handpiece made from an insulating material, such as a pens shell. You could also solder a M5 nut to the end of the damaged brass tube and use that as the threaded tip retainer. A brass nut would be best for this.

The brass hollow rod is pretty commonly available on eBay. It might be better to just buy a length and start again ?

Fraser
Title: Re: kWeld - "Next level" DIY battery spot welder
Post by: Kjelt on September 04, 2017, 03:18:28 AM
Simple fix there Kjelt is to retap with a recoil tap and put in a M5 insert, which uses almost the same diameter and which will recover most of the diameter and most of the strength. Not as good conductivity wise as it is stainless steel as opposed to brass
Thanks but the wall of the tube is 0,2mm left so it is to fragile to put anything in, I will visit the hardware junkyard or hardware store somewhere this week to find some alternative. I am not in a hurry since my main powersource is also still under development.

The brass hollow rod is pretty commonly available on eBay. It might be better to just buy a length and start again ?
If the store does not have or I can not find any alternative I will take a look. The problem with Ebay is that it takes sometimes 4 weeks before things show up  ;)
I do like your quick replacement idea though with the connectors, I do not know if I will need that since I won't be doing production type of welding anyway but good thought. I have no idea what the quality of those 150 connectors are, as long as it is cupper under the gold you won't have any issues.
Title: Re: kWeld - "Next level" DIY battery spot welder
Post by: tatus1969 on September 04, 2017, 03:30:23 AM
I've heard that the first pulse's purpose is to remove oils and other impurities, so the second pulse can perform the actual weld.

I'm by no means an expert in that area, but it sounds plausible. I'm not sure how to test it in practice.
Yes, and another rationale is to soften the nickel strip and let it sink to the battery tab through the tip pushing it down.

My experience is that I get consistent welding results from kWeld, no matter how hard I push down the electrodes. I also made welding tests on batteries from I which I had dremele'd away existing strips, which is dramatically changing their surface structure, and I still get the same results. I made some tests with solder flux in the path, and I already though about artificially aging/oxidizing some material. I'm most curious of the feedback on this topic from other kWeld builders.

Removed my post since it was my own stupid mistake. The taps were placed back in different order so I found just out while putting everything back that it was an M6 tap instead of an M5 tap I used.  |O
Since now one piece of the electrode brass pipe is damaged I have to find another way to construct the electrodes.
That was my first question because I was surprised that you said that there would only have been less than 1 mm remaining wall thickness. An M5 tap drill could not have caused that, because the tubes are 6mm outer diameter. Maybe you can source/make that brass tube yourself? Another builder has taken M8 brass threaded rod from his local hardware store. Anyway, you don't want to know all the mistakes (that are not on video) that I went through when starting this :o

using a pair of the XT-150 (or similar bullet connectors) at the probe tip
Interesting idea! When considering alternative probe systems, there is one unresolved thing that I have on my todo list. Even when all contact resistances and cross sections are perfect, the probes still heat up too quickly when doing higher energy welds like 100J. This is because copper is a very good thermal conductor and it sucks a lot of heat from the glowing weld spot itself. Thermal mass (larger structures like my initial probe design) only helps to delay this problem. Better insulation would help, for example a surrounding teflon tube, or better heat dissipation capability - a heat sink? Fan cooling?...

The drawback of using the XT-150 connectors for the probe tip mounting may be the connection resistance that it may introduce. They are gold plated and oxidisation resistant though.
During my torture tests, I continuously checked several temperatures. The XT150 did not get any hotter than the AWG8 wire.
Title: Re: kWeld - "Next level" DIY battery spot welder
Post by: tatus1969 on September 04, 2017, 04:57:03 AM
for anyone trying to buy the Turnigy nanotech battery. Hobbyking doesn't seem to be well organized. When searching globally, they say that it is out of stock. But the EU warehouse does have them: https://hobbyking.com/en_us/turnigy-battery-nano-tech-5000mah-3s-65-130c-lipo-pack-xt-90.html
Title: Re: kWeld - "Next level" DIY battery spot welder
Post by: Fraser on September 04, 2017, 05:20:10 AM
With regard to the thermal issue with prolonged use of the copper probes, I can see why this can become a proble.

I used to use Portisol Gas soldering irons and these utilised a clever axial heatsink at the base of the heated tip. This significantly reduced the heat to which the handle assembly was exposed. Pictures attached.

Sadly such a radial heatsink can make the probes bulky and harder to use.

Fraser
Title: Re: kWeld - "Next level" DIY battery spot welder
Post by: Fraser on September 04, 2017, 05:38:34 AM
There are many reansistor heatsink that may be pressed into service as a probe shaft heat disipator.

TO5 (8mm) is the most common fitting but smaller diameters are available.

Fraser
Title: Re: kWeld - "Next level" DIY battery spot welder
Post by: Fraser on September 04, 2017, 05:50:47 AM
Heatsink with 5mm hole down the centre. The outer diameter is a little too large though. You get the idea though  :)
Title: Re: kWeld - "Next level" DIY battery spot welder
Post by: tautech on September 04, 2017, 06:20:30 AM
A very useful (to me) 8mm brass rod resource is broken ballcock arms. Farmers with stock water drinking troughs should have several in their scrap metal pile. Sometimes used in toilet cisterns too (if not plastic) and they usually have a 5/16" UNC thread on one end and are forged into a hockey stick shape on the other to act as a fulcrum on the plunger to shut off the water. ~10' (250mm) of 8mm brass rod in each piece.
All plumber and rural suppliers should have new shiny ones in stock that can be cut into the lengths you need.

Thinking outside the square can be useful.  ;)
Title: Re: kWeld - "Next level" DIY battery spot welder
Post by: tatus1969 on September 04, 2017, 06:53:17 AM
Heatsink with 5mm hole down the centre. The outer diameter is a little too large though. You get the idea though  :)
Thanks! I have these in mind as well, but I'll have to see how that looks in reality and how usable that arrangement will be.

p.s. that was my first ever soldering iron ages ago:
(http://www.eevblog.com/forum/projects/guesses-on-what-i-am-attempting-here/?action=dlattach;attach=347657)
Title: Re: kWeld - "Next level" DIY battery spot welder
Post by: tatus1969 on September 04, 2017, 08:22:58 AM
I'm curious if I can use this LiTiO (6S):
https://www.ev-power.eu/LTO-technology/Lithium-Titanate-Oxid-Battery-Cell-LTO-2-4V-30AH.html?cur=1 (https://www.ev-power.eu/LTO-technology/Lithium-Titanate-Oxid-Battery-Cell-LTO-2-4V-30AH.html?cur=1)

Price may not be competitive but my idea is:
- use 6S LTO battery pack in my car as a secondary battery (should have good cold temperature performance for cold starts)
- make this battery removable from car and use it as a occassional portable powersource (for kWeld...)
- charging would be done in car from alternator
I checked the specs, they say <1mOhm per cell. Whatever that means. If the reality is close to 1mOhm, they would be fine. You would probably charge them to <13V. Current would then be 13/(6+3.3) = 1400A.
Title: Re: kWeld - "Next level" DIY battery spot welder
Post by: SirJMD on September 04, 2017, 05:46:39 PM
I've heard that the first pulse's purpose is to remove oils and other impurities, so the second pulse can perform the actual weld.

I'm by no means an expert in that area, but it sounds plausible. I'm not sure how to test it in practice.
Yes, and another rationale is to soften the nickel strip and let it sink to the battery tab through the tip pushing it down.

My experience is that I get consistent welding results from kWeld, no matter how hard I push down the electrodes. I also made welding tests on batteries from I which I had dremele'd away existing strips, which is dramatically changing their surface structure, and I still get the same results. I made some tests with solder flux in the path, and I already though about artificially aging/oxidizing some material. I'm most curious of the feedback on this topic from other kWeld builders.

The strips and cells I've tested with are 3+ years, so there you have your age test ;)
I've ordered some new strips that I hope are pure nickel. Where did you get yours? I like the slot and dimples.

One limitation I've noticed is that the high current makes it difficult, if not impossible, to weld thin wires. They.. vaporize. I'd really like to be able to weld fuse wire, like Tesla uses.
Title: Re: kWeld - "Next level" DIY battery spot welder
Post by: tatus1969 on September 04, 2017, 07:32:56 PM
One limitation I've noticed is that the high current makes it difficult, if not impossible, to weld thin wires. They.. vaporize. I'd really like to be able to weld fuse wire, like Tesla uses.
The minimum pulse width is 50us, which would result in ~ 0.1 joulses (into 1mOhm). I'll make some tests, but I have the hope that it is just an issue with the minimum adjustable energy (2J). I already had received the suggestion to make the dial knob logarithmic, which would easily enable lowering that limit.
Title: Re: kWeld - "Next level" DIY battery spot welder
Post by: tatus1969 on September 04, 2017, 08:17:55 PM
ops, this is now re-arranged.
thanks for the correction
now even the short battery lead is making quite a ton of voltage spikes
To me this clearly shows the limitations of SPICE when using components this far beyond their ratings. Both voltage peak level and shape aren't even close to reality as shown in the scope screenshot. Thanks for the simulation, and let's continue this way, but at the moment I see my doubts confirmed.
Title: Re: kWeld - "Next level" DIY battery spot welder
Post by: SirJMD on September 04, 2017, 09:43:37 PM
One limitation I've noticed is that the high current makes it difficult, if not impossible, to weld thin wires. They.. vaporize. I'd really like to be able to weld fuse wire, like Tesla uses.
The minimum pulse width is 50us, which would result in ~ 0.1 joulses (into 1mOhm). I'll make some tests, but I have the hope that it is just an issue with the minimum adjustable energy (2J). I already had received the suggestion to make the dial knob logarithmic, which would easily enable lowering that limit.

Sounds great.

I was actually thinking that a rotary encoder, or simply up/down buttons, would work better than the current dial.
Title: Re: kWeld - &quot;Next level&quot; DIY battery spot welder
Post by: anishkgt on September 04, 2017, 10:18:25 PM
One limitation I've noticed is that the high current makes it difficult, if not impossible, to weld thin wires. They.. vaporize. I'd really like to be able to weld fuse wire, like Tesla uses.
The minimum pulse width is 50us, which would result in ~ 0.1 joulses (into 1mOhm). I'll make some tests, but I have the hope that it is just an issue with the minimum adjustable energy (2J). I already had received the suggestion to make the dial knob logarithmic, which would easily enable lowering that limit.

Sounds great.

I was actually thinking that a rotary encoder, or simply up/down buttons, would work better than the current dial.
Certainly a rotary encoder would be better than a pot. Can have precise numbers.


Www.Georgehobby.wordpress.com

Equipments: DSO104z, Hakko FX888D
Title: Re: kWeld - "Next level" DIY battery spot welder
Post by: tatus1969 on September 04, 2017, 10:54:39 PM
I was actually thinking that a rotary encoder, or simply up/down buttons, would work better than the current dial.
Certainly a rotary encoder would be better than a pot. Can have precise numbers.
On the list :-)
Title: Re: kWeld - "Next level" DIY battery spot welder
Post by: Fraser on September 05, 2017, 01:05:26 AM
Hi and Lo current range selection, in combination with the pot, should be enough for most battery welding tasks.

Welding metal with high currents is not normally a task that required precise setting of the energy. Near enough is good enough in most cases. Sure a rotary encoder is nice as it can be the press switch type to select various stepped menu's. But do we really need lots of menu's in a battery tab welder ?

This is great fun, but we could be heading into 'Weld-nut" territory if we get too bound up in the desire for features and precision energy injection  ;D

I have no objection to improvements in the design though. It currently obeys the KISS principle though. Nice and easy to use  :) There could always be 'Standard' and 'Advanced' modes I suppose ?
To be honest, I am just very pleased with the design that Frank has come up with to date. If he decides to enhance the design further..... great, but I am already grateful for the time he has spent on this design for our benefit  :-+

Fraser
Title: Re: kWeld - "Next level" DIY battery spot welder
Post by: 3roomlab on September 05, 2017, 08:22:44 PM
To me this clearly shows the limitations of SPICE when using components this far beyond their ratings. Both voltage peak level and shape aren't even close to reality as shown in the scope screenshot. Thanks for the simulation, and let's continue this way, but at the moment I see my doubts confirmed.

*updated* i found the problem, and derived a messy way to solve it.

the main "model" that hit the spot is skin effect of the copper @ high freq (using lazy web calculators   :-// = 6.5um). i use this thickness to calculate the new resistance/impedance (=410m-ohm). this results in the new pulse shape, to enable the current capability, i created a subckt with alot of it in parallel (to get the right DC resistance). and then varied the weld spot resistance over time.

but i wonder if there is any transmission line expert willing to try this as a RF model?
i wonder, does my method count as a legit way to really simulate high frequency pulse in a welder?

*added* messy model of a 200 element "cable"
Title: Re: kWeld - "Next level" DIY battery spot welder
Post by: tatus1969 on September 06, 2017, 09:38:26 PM
the main "model" that hit the spot is skin effect of the copper @ high freq
I wouldn't be surprised at these high current, but are you sure that skin effect plays a role here? The MOSFET switching time is not very fast, rise time is 7 microseconds. (That is okay for the transistors even at this current level, switching loss is always less than 2000A * 30V * 7us = 0.42J.)

I think that the ~50V constant voltage in the oscilloscope screenshot is mainly caused by avalanche breakdown of the six large MOSFETs. The freewheeling diode does its best but it can only divert a fraction of the current through it. The combined die size of the six MOSFETs is approx 80 mm^2, that of the diode is much smaller.
Title: Re: kWeld - "Next level" DIY battery spot welder
Post by: tatus1969 on September 06, 2017, 10:03:17 PM
I've got new results from the capacitor based supply. Same basic procedure: repeated 50J pulses into a 1mOhm weld spot resistance. That resistance was a bit high this time (1.3mOhm), and the resulting pulse duration is approx 40ms.

During this test, the 5xBCAP0310 were kept topped at 12.5V by the HP server supply. There is no current control mechanism yet, so I assume that the PSU went to its current limit of 100A during recharge. When I pulse faster than maybe once a second, it shuts down after a few pulses.

The caps receive approx 1050A^2 * (5*1.5mOhm) * 40ms = 330J during each pulse, so I decided to fan-cool them and limit the pulse rate to once every 4 seconds. The results are as follows (ambient=25°C, I hadn't let them cool down from a previous test):

(http://www.eevblog.com/forum/projects/guesses-on-what-i-am-attempting-here/?action=dlattach;attach=348412)

There is some more headroom (max 70°C), but this shows me that a 5S configuration is not capable enough. On the other hand, I could not see any degradation or damage from this abuse because the current indicates that their ESR is not rising:

(http://www.eevblog.com/forum/projects/guesses-on-what-i-am-attempting-here/?action=dlattach;attach=348414)

I did some calculations, and a 3S2P configuration will reduce the energy loss per 50J pulse to 113J, which is only one third of what it is now. This will allow my targeted pulse rate of once per second. But how to charge them? I don't really want to go for the additional cost of a 70A step down converter...
Title: Re: kWeld - "Next level" DIY battery spot welder
Post by: Kjelt on September 06, 2017, 10:23:26 PM
So how many F's should the caps be for 5S to be ok ? The BCAP0350 are also around €10.- (but higher ESR of 3,2mOhms)
The ones above that double the F's (650) but start to go to three times the price  :(
But is it allowed to just put two strings parallel ? Then 5SP2 would be a mediate option for around €100.- total cost
Title: Re: kWeld - "Next level" DIY battery spot welder
Post by: Fraser on September 06, 2017, 10:29:28 PM
Yay! My kWeld arrived today  :D

I delayed its despatch due to being on holiday. Thanks Frank, it's perfect  :-+

Now to find some time to build it into a complete system.

Fraser
Title: Re: kWeld - "Next level" DIY battery spot welder
Post by: tatus1969 on September 07, 2017, 02:20:00 AM
So how many F's should the caps be for 5S to be ok ? The BCAP0350 are also around €10.- (but higher ESR of 3,2mOhms)
The ones above that double the F's (650) but start to go to three times the price  :(
But is it allowed to just put two strings parallel ? Then 5SP2 would be a mediate option for around €100.- total cost
A 5S2P configuration would lose 187J per weld pulse. The more cells added in series, the more the losses. I have attached the spreadsheet that I made for my estimations. The 650F model can also be used in place of two BCAP0310, but as you say the price isn't as good. I don't recommend the BCAP0350 because of its higher ESR.

I'm currently digging into a two-phase sync buck converter.

Yay! My kWeld arrived today  :D
Great! :-+

Title: Re: kWeld - "Next level" DIY battery spot welder
Post by: wire.rat on September 07, 2017, 02:26:03 AM
Hi all,

I would recommend this probe that i bought from taobao.com. It has served be very well in the past 6 month with my chinese Transformer spot welder , and it comes with a thick copper cable and connectors and only a little warm after 200 welds with 0.15mm pure nickel strips/
The probes cost about 30USD before shipping and I think it is really worth the money.
The welding pins can be easily bought from taobao, so theres no shortage of supply there.
The Welding Probes initially came as a pair enclosed in a plastic part that holds them together, but i have taken them apart to get more precise moment with them

Here's some photos of my spot welder, probes and photos of the welds that i get with the probes and the item page on taobao. If anyone needs it, i can help to order and ship them.

http://imgur.com/a/N8x5L (http://imgur.com/a/N8x5L)

I will be adding photos of the welds after i finish welding a 16S5P battery using LG F1L 18650 cells in a couple of hours!

https://item.taobao.com/item.htm?spm=a230r.1.14.33.76bf5238gg0NQ&id=539313013540&ns=1&abbucket=17#detail (https://item.taobao.com/item.htm?spm=a230r.1.14.33.76bf5238gg0NQ&id=539313013540&ns=1&abbucket=17#detail)
Title: Re: kWeld - "Next level" DIY battery spot welder
Post by: SirJMD on September 10, 2017, 05:22:32 AM
A bit more testing done. It's possible to weld thin copper wires at 2 joules.

The weld on the right is were done by placing one electrode on the wire and the other on the battery.
The two other welds (right and middle) were done by placing both electrodes on the wire. It's clear that a fair amount of the energy was lost in the copper wire (discolored).

(http://peecee.dk/uploads/092017/weld.jpg)
Title: Re: kWeld - "Next level" DIY battery spot welder
Post by: romantao on September 11, 2017, 11:14:52 PM
Hi everyone,

Just wanted to share my recent experience with the Kweld.

I assembled my system and connected it to a 12V 65Ah Lead acid battery

http://www.ultracell.co.uk/datasheets/uxlseries/UXL65-12.pdf (http://www.ultracell.co.uk/datasheets/uxlseries/UXL65-12.pdf)

I made a 34cm extension cord connected to the kit using this connector
http://www.mouser.com/ds/2/22/DS-SB50(5) (http://www.mouser.com/ds/2/22/DS-SB50(5))[1]-482233.pdf and its crimps
http://pt.mouser.com/ProductDetail/Anderson-Power-Products/5952-BK/?qs=sGAEpiMZZMtjzVbpKqo2YZRH3O%252bLIhj7nHGm4CGYoVc%3d (http://pt.mouser.com/ProductDetail/Anderson-Power-Products/5952-BK/?qs=sGAEpiMZZMtjzVbpKqo2YZRH3O%252bLIhj7nHGm4CGYoVc%3d)

The connector and contacts are rated for 120A continuous.

A weld test over a nickel strip of 0.15mm is reporting:

E=65.3J
I=1002
R=1.43mOhm
t=54.27ms

Here are some photos of my prototype. Its so much easy to work with a tool like this (previously I was using a sunkko but it was not fit for this job)

Regards
Title: Re: kWeld - "Next level" DIY battery spot welder
Post by: tatus1969 on September 12, 2017, 12:52:36 AM
A bit more testing done. It's possible to weld thin copper wires at 2 joules.
Sounds good! If you are more interested in lower energies, then I would prepare a logarithmic firmware that goes down to 0.5J (lower values do not make sense because the min pulse width is 50us). You would need to wire up one of these www.ebay.de/itm/252757338778 (http://www.ebay.de/itm/252757338778), or buy my programming adapter kit: https://www.kicksurfer.de/index.php/product/kweld-firmware-update-tool/ (https://www.kicksurfer.de/index.php/product/kweld-firmware-update-tool/)
Title: Re: kWeld - "Next level" DIY battery spot welder
Post by: Fraser on September 12, 2017, 01:24:25 AM
Romantao,

Nice work  :-+

Fraser
Title: Re: kWeld - "Next level" DIY battery spot welder
Post by: maukka on September 12, 2017, 01:53:20 AM
Got mine too and it's working perfectly with the Turnigy nano-tech 3S 5000mAh battery (https://hobbyking.com/en_us/turnigy-battery-nano-tech-5000mah-3s-65-130c-lipo-pack-xt-90.html?___store=en_us) Frank also suggested. First I tried a too overkill of a lipo (https://hobbyking.com/en_us/graphene-6000mah-6s-65c-w-xt90.html), which just activated the overcurrent protection (or exploded with sparks and a bang on the electrodes, wife says thanks for the heart attack) during the calibration phase.

15-20 Joules seemed enough for 0.15mm strips (used some old one ripped from packs for testing). ~1200-1350A measured.

(http://i.imgur.com/4etA1kq.jpg)
Title: Re: kWeld - "Next level" DIY battery spot welder
Post by: SirJMD on September 12, 2017, 06:29:47 AM
A bit more testing done. It's possible to weld thin copper wires at 2 joules.
Sounds good! If you are more interested in lower energies, then I would prepare a logarithmic firmware that goes down to 0.5J (lower values do not make sense because the min pulse width is 50us). You would need to wire up one of these www.ebay.de/itm/252757338778 (http://www.ebay.de/itm/252757338778), or buy my programming adapter kit: https://www.kicksurfer.de/index.php/product/kweld-firmware-update-tool/ (https://www.kicksurfer.de/index.php/product/kweld-firmware-update-tool/)

I think 1 joule might be the sweet spot for the thin wires. 2 joule melted the wire a bit too much.
Title: Re: kWeld - "Next level" DIY battery spot welder
Post by: Fraser on September 12, 2017, 06:39:06 AM
Can the firmware provide a 1 Joule to full power operating range without losing too much resolution ?

In the 'good ol' days' we used to use multi turn potentiometers in applications where a 270 degrees pot was too great a change in resistance per degree for a task. I might fit a 10 turn pot on my unit  ;D  Modern techniques use encoders as has already been suggested. I still like the Hi/Lo range switch option though.

Fraser
Title: Re: kWeld - "Next level" DIY battery spot welder
Post by: tatus1969 on September 12, 2017, 08:08:18 AM
Can the firmware provide a 1 Joule to full power operating range without losing too much resolution ?
I'm sure it can, I'll test making the dial behaving exponentially tomorrow. Attached the spreadsheet for the intended formula. First 20%: 7J, then: 19J .. 48J .. 121J .. 304J. At 500J you don't care for milliJoules.

Title: Re: kWeld - "Next level" DIY battery spot welder
Post by: ovnr on September 12, 2017, 08:52:37 AM
Tatus: I haven't kept up with the thread as much as I probably should have, but any plans for another batch of kWelds?
I wanted one, but had already spent a bit too much money on other frivolous things that month.
Title: Re: kWeld - "Next level" DIY battery spot welder
Post by: ozwolf on September 12, 2017, 08:58:42 AM
Tatus: I haven't kept up with the thread as much as I probably should have, but any plans for another batch of kWelds?
I wanted one, but had already spent a bit too much money on other frivolous things that month.

Same here...
Title: Re: kWeld - "Next level" DIY battery spot welder
Post by: HackedFridgeMagnet on September 12, 2017, 09:07:16 AM
+1 for me
Title: Re: kWeld - "Next level" DIY battery spot welder
Post by: tatus1969 on September 12, 2017, 08:29:13 PM
+1 for me
Tatus: I haven't kept up with the thread as much as I probably should have, but any plans for another batch of kWelds?
I wanted one, but had already spent a bit too much money on other frivolous things that month.

Same here...
Tatus: I haven't kept up with the thread as much as I probably should have, but any plans for another batch of kWelds?
I wanted one, but had already spent a bit too much money on other frivolous things that month.
I'm already busy sourcing components : :)
Title: Re: kWeld - "Next level" DIY battery spot welder
Post by: tatus1969 on September 13, 2017, 02:06:16 AM
A customer had reported a kWeld that had its main voltage regulator broken (see picture). He is using a 6S Lipo instead of the recommended 3S. After some research, I realized that I paid much attention to the robustness of the power switch while overlooking what is happening at the battery terminals. Of course that also sees high voltage spikes from inductive kickback, which is exceeding the main regulator's input voltage ratings.

Although it never happened to me during all my experiments that the regulator broke down, I highly recommend applying the modification that I summarized in the attached document. If you do not have the resources to do this by yourself, then of course I offer to have the unit sent back to me, modified, and delivered back to you, all free of charge.

(https://endless-sphere.com/forums/download/file.php?id=221489)
Title: Re: kWeld - "Next level" DIY battery spot welder
Post by: Fraser on September 13, 2017, 02:20:15 AM
Frank,

You are a true Gentleman. It is obvious from your posts.

Your design is, by its very nature, a kind of ongoing development project. It is not unreasonable to expect the odd issue or two, in spite of your careful and thorough testing before production.

If I were wishing to return a board to you for rework, I would want to pay all postage costs. It just seems unfair to expect you to pay such on this project. It is not like you are making some huge profit on the kit is it ! That is just my old fashioned way I suppose. I can implement any changes needed myself anyway so you will not be receiving a board from me :)

Keep up the great work and thank you again for sharing this excellent project with us. Doing so risks experiencing undiscovered issues that can be a hassle to sort out for 'customers'. I hope you do not suffer any hassle due to sharing your unit with us. You do not deserve such.

Fraser
Title: Re: kWeld - "Next level" DIY battery spot welder
Post by: SirJMD on September 13, 2017, 04:24:34 AM
A customer had reported a kWeld that had its main voltage regulator broken (see picture). He is using a 6S Lipo instead of the recommended 3S. After some research, I realized that I paid much attention to the robustness of the power switch while overlooking what is happening at the battery terminals. Of course that also sees high voltage spikes from inductive kickback, which is exceeding the main regulator's input voltage ratings.

Although it never happened to me during all my experiments that the regulator broke down, I highly recommend applying the modification that I summarized in the attached document. If you do not have the resources to do this by yourself, then of course I offer to have the unit sent back to me, modified, and delivered back to you, all free of charge.

(https://endless-sphere.com/forums/download/file.php?id=221489)

Very nice of you to support your "customers" the way you offer to. Highly appreciated.

Great work!
Title: Re: kWeld - "Next level" DIY battery spot welder
Post by: tatus1969 on September 13, 2017, 06:57:09 AM
Your design is, by its very nature, a kind of ongoing development project. It is not unreasonable to expect the odd issue or two, in spite of your careful and thorough testing before production.
Yes, which is why I wanted to wait for your all feedback and also you all (ab)using it, before ordering a next, larger batch. Although I should do this timely, there are so many people knocking on my door now  :)
Title: Re: kWeld - "Next level" DIY battery spot welder
Post by: Fraser on September 13, 2017, 07:07:34 AM
Frank,

I will always be using my kWeld on 14V or less so is there any reason why I should not fit a lower voltage TVS better matched to my maximum intended supply ? I was thinking of one that engaged at say 20V and fully clamped at say around 22V. It's working voltage of 18V would prevent any unwelcome issues with a fully charged car battery p.d.

Best Wishes

Fraser
Title: Re: kWeld - "Next level" DIY battery spot welder
Post by: tatus1969 on September 13, 2017, 07:16:23 AM
Frank,

I will always be using my kWeld on 14V or less so is there any reason why I should not fit a lower voltage TVS better matched to my maximum intended supply ? I was thinking of one that engaged at say 16V and fully clamped at say around 20V.

Best Wishes

Fraser
Yes, that would leave much more safety margin. And it would also allow you using a PTC / resettable fuse of lets say 0.5~2 ohm instead of a resistor. The 10 ohm resistor adds ~0.5V of voltage drop from the battery (operating current is 40-50mA, with pulses of ~300mA during holdup capacitor recharge). I'll revise the entire supply circuit in the next revision, and tend to use a linear regulator with enough input voltage rating instead. Power dissipation will be 1W at 30V, but who cares at welding power in the kW range...
Title: Re: kWeld - "Next level" DIY battery spot welder
Post by: Fraser on September 13, 2017, 07:48:02 AM
Many thanks Frank. That is what I will do on my kWeld them.

Fraser
Title: Re: kWeld - "Next level" DIY battery spot welder
Post by: anishkgt on September 13, 2017, 11:19:15 AM
silly question here. Forgive me for that.

what does the ohm mean here ? resistance of the nickel between the two points at which the elctrodes touch ? or the wire during weld ?
Title: Re: kWeld - "Next level" DIY battery spot welder
Post by: tatus1969 on September 13, 2017, 05:21:46 PM
silly question here. Forgive me for that.

what does the ohm mean here ? resistance of the nickel between the two points at which the elctrodes touch ? or the wire during weld ?
It displays the measured resistance between the electrode tips. EDIT: this is true when welding. During calibration, it displays the combined wiring/electrode holder resistance at the output. So somehow both of your answers are correct. And it shows that your question was not silly  :)
Title: Re: kWeld - "Next level" DIY battery spot welder
Post by: tatus1969 on September 13, 2017, 07:10:23 PM
Many thanks Frank. That is what I will do on my kWeld them.
One more thought: a 0.5R polyfuse is maybe too little resistance. You have to assume that the inductively driven voltage at the input is ~50V. When your TVS clamps at 20V, then the current would be (50-20)/0.5=60A. If the TVS can sufficiently clamp this current, then you're fine. Otherwise it may be wise to increase the resistance. At 2 Ohms, the current is reduced to 15A which I like much more. Power dissipation is not an issue, because the voltage spikes last less than 20 microseconds.
Title: Re: kWeld - "Next level" DIY battery spot welder
Post by: Fraser on September 13, 2017, 08:49:23 PM
Hi Frank,

Thanks for the advice. I will add a little resistance as you suggest.

I have elected to use a P6KE18A TVS rated at 100A so it is quite robust. I already have them in my component stock so may as well use them 🙂

Best Wishes

Fraser
Title: Re: kWeld - "Next level" DIY battery spot welder
Post by: anishkgt on September 14, 2017, 01:23:13 AM
Maybe a bit off topic.

Just need to clear my doubts on getting amps and resistance put into the nickel strips by this formula
I = U * diameter [mm2] / (0.0175 * length [m])

with that i get this result
I = 0.29 * 25 / (0.0175 * 0.13)
  = 3,186A for 20ms


How true is this ? i did start a thread on this but am just curious and lost at the same time as to how to calculate it without any additional components or costly gadgets.
Title: Re: kWeld - "Next level" DIY battery spot welder
Post by: tatus1969 on September 14, 2017, 03:02:35 AM
I = 0.29 * 25 / (0.0175 * 0.13)
Please elaborate more on the numbers, except for the specific resistance of copper (not nickel) I cannot see how you came to them.
Title: Re: kWeld - "Next level" DIY battery spot welder
Post by: anishkgt on September 14, 2017, 03:16:50 AM
Oh i am sorry that i missed that out

I = 0.29 * 25 / (0.0175 * 0.13)
V = 0.29 (on a cable with two tapping 13cm apart)
size of cable in mm2 = 25
0.0175 is a constant (not sure what it is but i got the formula from here http://avdweb.nl/contact/12-contacts/1-avandalen.html (http://avdweb.nl/contact/12-contacts/1-avandalen.html))
distance between two taps on the cable = 13cm (here 0.13m)
Title: Re: kWeld - "Next level" DIY battery spot welder
Post by: SirJMD on September 14, 2017, 06:33:46 AM
Just finished testing copper strips and copper wire. No success at all. I think the copper conducts way too good.
Title: Re: kWeld - "Next level" DIY battery spot welder
Post by: tatus1969 on September 14, 2017, 07:26:23 PM
Just finished testing copper strips and copper wire. No success at all. I think the copper conducts way too good.
I did some quick research on this. To weld copper strips, one supposedly needs 2500A+, tungsten electrodes, an inert gas. There is also an interesting thread here: https://endless-sphere.com/forums/viewtopic.php?t=84680
Title: Re: kWeld - "Next level" DIY battery spot welder
Post by: tatus1969 on September 14, 2017, 07:29:07 PM
Oh i am sorry that i missed that out

I = 0.29 * 25 / (0.0175 * 0.13)
V = 0.29 (on a cable with two tapping 13cm apart)
size of cable in mm2 = 25
0.0175 is a constant (not sure what it is but i got the formula from here http://avdweb.nl/contact/12-contacts/1-avandalen.html (http://avdweb.nl/contact/12-contacts/1-avandalen.html))
distance between two taps on the cable = 13cm (here 0.13m)
That is Ohm's law combined with https://en.wikipedia.org/wiki/Electrical_resistivity_and_conductivity
Title: Re: kWeld - "Next level" DIY battery spot welder
Post by: anishkgt on September 14, 2017, 07:30:42 PM
Yes but how reliable would it be ?
Title: Re: kWeld - "Next level" DIY battery spot welder
Post by: tatus1969 on September 14, 2017, 07:33:15 PM
Yes but how reliable would it be ?
What do you mean by that?
Title: Re: kWeld - "Next level" DIY battery spot welder
Post by: anishkgt on September 14, 2017, 07:34:50 PM
I mean can we determine the amp draw using this method, that is with that formula ?
Title: Re: kWeld - "Next level" DIY battery spot welder
Post by: tatus1969 on September 14, 2017, 07:36:28 PM
I mean can we determine the amp draw using this method, that is with that formula ?
Did you take the time to understand the wiki article and relate it to the formula? That should answer your question.
Title: Re: kWeld - "Next level" DIY battery spot welder
Post by: anishkgt on September 16, 2017, 04:54:12 AM
well i did read it but with lack of knowledge on them i was lost if this road would be correct.
Title: Re: kWeld - "Next level" DIY battery spot welder
Post by: tatus1969 on September 16, 2017, 05:07:27 PM
well i did read it but with lack of knowledge on them i was lost if this road would be correct.
It is only Ohms law, R=V/I, and the specific resistance of copper, R= 0.0175 * length / crosssection.  :-//
Title: Re: kWeld - "Next level" DIY battery spot welder
Post by: tatus1969 on September 16, 2017, 05:42:43 PM
well i did read it but with lack of knowledge on them i was lost if this road would be correct.
It is only Ohms law, R=V/I, and the specific resistance of copper, R= 0.0175 * length / crosssection.  :-//
By the way. It seems that you want to copy my invention of using an energy metering approach into your design. If you do this for yourself, I am fine with that, but if you want to implement and sell it and by this damage my business, I would find this very immoral. I am not a large company that has enough money and doesn't care about this, but a husband and father trying to make a living from this and other projects in a self employed business.
Title: Re: kWeld - "Next level" DIY battery spot welder
Post by: anishkgt on September 16, 2017, 06:22:19 PM
Oh Tatus i had begun this project of mine a year back and they are not based on the capacitve discharge welding, rather they work on ac and determining the amp drawn was harder where the ac had to be rectified and then fed into the MCU and again there would be voltage drop down the way.

I brought this question up because it was done here http://avdweb.nl/contact/12-contacts/1-avandalen.html (http://avdweb.nl/contact/12-contacts/1-avandalen.html) and wish to know how true it was by asking for others opinion. It had nothing to with your project and in fact am not going to add it into my either though the approach to it is totally different. Was only shedding some light to it so maybe yourself or others could make use of it.

Secondly i know how hard to sell something to some pennies out of it. I had sold quite a few of earlier spot welders. I have the second version pcbs with me that i had posted here in the forum http://www.eevblog.com/forum/manufacture/some-china-pcb-manufacturer-recommend/50/ (http://www.eevblog.com/forum/manufacture/some-china-pcb-manufacturer-recommend/50/).

I too am a dad and a husband but this is not my primary job i work in the IT industry and these are just my hobby which am interested in with that said i do not copy and paste ideas, i try to do it my way with my own ideas. So Tatus need not worry about copy your ideas or designs into mine. :)


Hope that clears your mind.
Title: Re: kWeld - "Next level" DIY battery spot welder
Post by: anishkgt on September 16, 2017, 06:55:41 PM
Impressive project by the way Tatus :clap:. Seems one of a kind and i hope this would bring you fortune. :-+ As far as i have read, growth and fame has always begun in a closed small room, a grage or in the basement.
Title: Re: kWeld - "Next level" DIY battery spot welder
Post by: tatus1969 on September 16, 2017, 07:20:52 PM
Impressive project by the way Tatus :clap:. Seems one of a kind and i hope this would bring you fortune. :-+ As far as i have read, growth and fame has always begun in a closed small room, a grage or in the basement.
Thanks, in this case it would an attic  8)
Title: Re: kWeld - "Next level" DIY battery spot welder
Post by: anishkgt on September 16, 2017, 07:22:18 PM
Impressive project by the way Tatus :clap:. Seems one of a kind and i hope this would bring you fortune. :-+ As far as i have read, growth and fame has always begun in a closed small room, a grage or in the basement.
Thanks, in this case it would an attic  8)


ha ha ha  :-DD that is a close match to 'closed small room'
Title: Re: kWeld - "Next level" DIY battery spot welder
Post by: mazzic518 on September 17, 2017, 10:11:58 AM
I definitely want one looking forward to the second batch.
Title: Re: kWeld - "Next level" DIY battery spot welder
Post by: Mikko Saarisalo on September 19, 2017, 04:45:10 AM
+1 for the waiting list for next production run.  I would not mind making and paying a pre-order for one or two units.

(Just registered to this site for this very purpose... :) )

cheers
-mikko
Title: Re: kWeld - "Next level" DIY battery spot welder
Post by: mcinque on September 25, 2017, 03:07:30 AM
SirJMD, my compliments to you about how you're handling this little issue with your customers  :-+

Can I take advantage of this post to ask you the role of this three components (D16,D6 and D7-12, TVSs and zener) in your schematic? TVS are there to clamp voltage of course, maybe to manage the wiring inductance kickback? And why the zener on the mosfets? Of course to protect them from overvoltages, but are they needed because of the inductive kickbacks coming from the welding pulses?

Sorry for my ingorance  ;D
Title: Re: kWeld - "Next level" DIY battery spot welder
Post by: tatus1969 on September 25, 2017, 09:51:39 PM
SirJMD, my compliments to you about how you're handling this little issue with your customers  :-+
Thanks  ;)

Can I take advantage of this post to ask you the role of this three components (D16,D6 and D7-12, TVSs and zener) in your schematic? TVS are there to clamp voltage of course, maybe to manage the wiring inductance kickback? And why the zener on the mosfets? Of course to protect them from overvoltages, but are they needed because of the inductive kickbacks coming from the welding pulses?

Sorry for my ingorance  ;D
Yes, the TVS is there to reduce the stress that the transistors see during inductive kickback at turn-off. The zeners are there to protect the MOSFET gates from overvoltage. As I had to assume fast transients at their drains, and the gates are only loosely driven, I am afraid of gate overvoltage from charge build up through their Miller capacitances.
Title: Re: kWeld - "Next level" DIY battery spot welder
Post by: Fraser on September 25, 2017, 10:55:51 PM
When dealing with high energies, the 'belt and braces' approach is more than justified  :-+

I would place TVS diodes all over the unit if I thought it were needed, but you have already come up with an excellent robust design.

Sadly my kit is still in its box awaiting its turn on my to-do list.

Off topic but maybe of interest ?

I was demonstrating my Chinese Transformer based battery tab welder to my neighbour at the weekend. My first weld resulted in a loud BANG, from inside the unit and its lights went out. I thought I had blown the fuse but no, it was fine. House power was still on as well. The give-away was the lack of the neon light on the power switch ..... no mains power was getting to it.

A quick look inside revealed no smell of burning or obvious failure. A continuity check proved that the mains power cable Neutral wire was open circuit. Further investigation revealed that the blue insulation on the wire after it entered the units case looked slightly discoloured white in a couple of places. I pulled on the cable and the insulation could be seen to stretch ! I cut open the wires insulation and found just white powder inside at two separate locations. The copper wire had turned to powder ! No signs of heat damage.... the copper was gone. I looked at the cable quality and found that the manufacturer had used really low current cable with very little copper cross sectional area and very fine strands in the insulated wires. I am not certain of the failure mode, be it corrosion or gradual erosion of the fine wires, but it gave up in the end. I am fitting decent quality 13A rated cable to it instead.

Fraser
Title: Re: kWeld - "Next level" DIY battery spot welder
Post by: tatus1969 on September 27, 2017, 04:50:39 AM
Sadly my kit is still in its box awaiting its turn on my to-do list.
Then it's time to let the Tiger out  ;)

a loud BANG, from inside the unit and its lights went out.
That reassures me to continue my work! I am busy sourcing components for a 100 unit production batch.
Title: Re: kWeld - "Next level" DIY battery spot welder
Post by: Southerner on September 27, 2017, 05:32:11 AM

That reassures me to continue my work! I am busy sourcing components for a 100 unit production batch.
Do you have an estimated cost for the next batch?  I would be interested in one.
Title: Re: kWeld - "Next level" DIY battery spot welder
Post by: tatus1969 on September 27, 2017, 05:33:43 AM

That reassures me to continue my work! I am busy sourcing components for a 100 unit production batch.
Do you have an estimated cost for the next batch?  I would be interested in one.
I'll publish that once I have all prices from my suppliers. I expect that to be completed in 1-2 weeks from now.
Title: Re: kWeld - "Next level" DIY battery spot welder
Post by: tatus1969 on September 27, 2017, 06:32:59 PM
Guess what this will become  8)

(http://www.eevblog.com/forum/projects/guesses-on-what-i-am-attempting-here/?action=dlattach;attach=355097)

(http://www.eevblog.com/forum/projects/guesses-on-what-i-am-attempting-here/?action=dlattach;attach=355099)
Title: Re: kWeld - &quot;Next level&quot; DIY battery spot welder
Post by: Bratster on September 27, 2017, 06:40:57 PM
Capacitor charging interface for a server power supply?

Sent from my Nexus 6 using Tapatalk

Title: Re: kWeld - "Next level" DIY battery spot welder
Post by: Kjelt on September 28, 2017, 12:27:23 AM
A raspberry pi / beaglebone  kWeld shield?  :popcorn:
Title: Re: kWeld - &quot;Next level&quot; DIY battery spot welder
Post by: tatus1969 on September 29, 2017, 07:56:34 AM
Capacitor charging interface for a server power supply?
Bang on!

A raspberry pi / beaglebone  kWeld shield?  :popcorn:
Would that be another product idea?  ;)
Title: kWeld - "Next level" DIY battery spot welder
Post by: anishkgt on September 29, 2017, 07:58:56 AM
Curious, which cad do you use to get those 3D images ?


Www.Georgehobby.wordpress.com

Equipments: DSO104z, Hakko FX888D
Title: Re: kWeld - "Next level" DIY battery spot welder
Post by: tatus1969 on September 29, 2017, 08:53:25 PM
Curious, which cad do you use to get those 3D images ?
I'm using old-fashioned Eagle and export into Sketchup.
Title: Re: kWeld - &quot;Next level&quot; DIY battery spot welder
Post by: anishkgt on September 29, 2017, 09:00:50 PM
Oh ok well that is a lot of work to do. Eagle is fine but moving it to sketchup is some work. I guess kicad is better with 3D but have to manually link the symbol to the layout.


Www.Georgehobby.wordpress.com

Equipments: DSO104z, Hakko FX888D
Title: Re: kWeld - &quot;Next level&quot; DIY battery spot welder
Post by: tatus1969 on September 29, 2017, 09:09:48 PM
Oh ok well that is a lot of work to do. Eagle is fine but moving it to sketchup is some work. I guess kicad is better with 3D but have to manually link the symbol to the layout.
the export/import is automatic, you just have to download or draw the objects. I get most of them through the warehouse, some of them are STEP files from the manufacturers. For this project, I didn't draw a single object from scratch. The biggest work was refining the heat sinks, as the manufacturer model only had a solid block instead of the fins.

I only wish that I had done that before ordering the PCBs. Look closer how the large connector's pins poke through the board :wtf:
Title: Re: kWeld - &quot;Next level&quot; DIY battery spot welder
Post by: anishkgt on September 29, 2017, 09:13:20 PM
Yea can be quite hard. I guess some day I'll have to start with kicad just because of the new licensing of eagle and the advantage of 3D rendering of kicad. If altium was cheaper would have taken that.


Www.Georgehobby.wordpress.com

Equipments: DSO104z, Hakko FX888D
Title: Re: kWeld - &quot;Next level&quot; DIY battery spot welder
Post by: tatus1969 on October 01, 2017, 10:46:35 PM
Capacitor charging interface for a server power supply?
The boards from Elecrow have arrived much earlier than I expected. Ordered on 23rd, received on 27th. :-+

Although I have to work on sourcing components for kWeld, I couldn't resist to build and power up one. It instantly came up with all four phases, and voltage regulation also works already ;D

Target specs: output voltage 6-10V adjustable (the design can do 0-12), current 0-80A adjustable. The design can operate in CV and CC modes. It fits all HP DPB800GB DPS800GB server PSU models that I found so far on the internet.

Apart from being a high power super capacitor charger, it can also be used to build a 12V / 80A current limited PSU for less than 100€.

I'll have to see how much current the design can do continuously, but it has a temperature monitoring circuit that linearly reduces current and regulates a max temperature. This makes it suitable for permanent short circuit under all load conditions.

(http://www.eevblog.com/forum/projects/guesses-on-what-i-am-attempting-here/?action=dlattach;attach=356373)
Title: Re: kWeld - "Next level" DIY battery spot welder
Post by: Fraser on October 01, 2017, 10:55:15 PM
Nice work Frank  :-+

Very neat design.

Fraser
Title: Re: kWeld - &quot;Next level&quot; DIY battery spot welder
Post by: anishkgt on October 01, 2017, 11:08:04 PM
Good job frank. With a little mode I guess it should fit other psu as well. But don't you think the power supply for kweld is a bit oversized. Just my opinion.


Www.Georgehobby.wordpress.com

Equipments: DSO104z, Hakko FX888D
Title: Re: kWeld - &quot;Next level&quot; DIY battery spot welder
Post by: tatus1969 on October 02, 2017, 12:37:48 AM
Good job frank. With a little mode I guess it should fit other psu as well. But don't you think the power supply for kweld is a bit oversized. Just my opinion.
I want the system to allow welding at 50J with one second repetition rate. This means that the PSU needs to supply 50J / 0.1 * 1sec = 500W on average. (The 0.1 is the system efficiency)
Title: Re: kWeld - &quot;Next level&quot; DIY battery spot welder
Post by: anishkgt on October 02, 2017, 12:42:02 AM
Cool sounds good enough.


Www.Georgehobby.wordpress.com

Equipments: DSO104z, Hakko FX888D
Title: Re: kWeld - "Next level" DIY battery spot welder
Post by: joddi on October 04, 2017, 11:12:46 AM
I want the system to allow welding at 50J with one second repetition rate. This means that the PSU needs to supply 50J / 0.1 * 1sec = 500W on average. (The 0.1 is the system efficiency)

Nice target, but it also means your whole system has to be capable to disipate continuously 500W of heat somewhere...

I'm waiting for next batch of your electronics to order one. I need to weld copper braid to brass sheet with oposite electrodes, so probably more pulse energy will be necessary, but I don't care much about repetition rate (30s would be ok). I'm thinking of 500J pulses or maybe more and I'm prepared to double power MOSFET switch if necessary.
Title: Re: kWeld - "Next level" DIY battery spot welder
Post by: tatus1969 on October 04, 2017, 07:42:02 PM
your whole system has to be capable to disipate continuously 500W of heat somewhere...
Most of the heat is dissipated in the super capacitors, which is why they will receive a decent fan. And this 50J/1sec target is not a continuous one, because the electrodes also receive substantial heat from the weld spot itself. A fixed electrode system could handle this, but the handheld system needs regular cooling breaks. I have set the 1sec goal because I do not want to limit the usability because one constantly had to wait for the capacitors to recharge.

I'm waiting for next batch of your electronics to order one. I need to weld copper braid to brass sheet with oposite electrodes, so probably more pulse energy will be necessary, but I don't care much about repetition rate (30s would be ok). I'm thinking of 500J pulses or maybe more and I'm prepared to double power MOSFET switch if necessary.
I don't think that kWeld is up to this task. I tried to weld two 0.1mm copper sheets together without success. Copper requires a significantly higher output power, and 1500A is not enough.
Title: Re: kWeld - &quot;Next level&quot; DIY battery spot welder
Post by: anishkgt on October 04, 2017, 08:19:39 PM
Kweld is intended for battery tab spot welding. Maybe you could do a diy spot welder with a MOT.


Www.Georgehobby.wordpress.com

Equipments: DSO104z, Hakko FX888D
Title: Re: kWeld - "Next level" DIY battery spot welder
Post by: tatus1969 on October 07, 2017, 04:08:53 AM
The capacitor charger test load has arrived, and I couldn't resist to make a first test with a higher load. Results: 35A at 8.5V -> 297W. Hottest spot of the charger are the large heat sink and the inductors: 50°C. It amazes me how small power circuits can be with modern components  8)

Sadly, I had to stop here because the server PSU seems to have problems, it reaches 105°C at one spot of its PCB. I'll have to solve that before continuing. I have another ten bulbs waiting (these are 50W).
Title: Re: kWeld - &quot;Next level&quot; DIY battery spot welder
Post by: anishkgt on October 07, 2017, 04:59:10 AM
That's a lot of work your going through frank but I guess it's part of the fun and it pays off at the end


Www.Georgehobby.wordpress.com

Equipments: DSO104z, Hakko FX888D
Title: Re: kWeld - &quot;Next level&quot; DIY battery spot welder
Post by: tatus1969 on October 07, 2017, 07:30:14 AM
it's part of the fun and it pays off at the end
Definitely the fun, but I am also learning a lot. This is my first four phase buck converter, and the amperage is also an order of magnitude more than what I did before. I am also using Infineon's OptiMOS5 MOSFETS for the first time. They are extremely fast, have integrated snubbers, and their diode reverse recovery charge (that quickly causes ringing/EMI problems) is lower than everything else that I know. I have attached pictures from one of the switch nodes at 35A load current, clean as a whistle.

And I hope that it will also pay off, not necessarily only as an accessory for the welder, but also as a high power laboratory supply. A regular 0-12V 0-80A lab supply can easily hit 1000€ or more, this one an order of magnitude cheaper.

And last but not least, I am developing an own business as an engineering service provider, and am collecting references.
Title: kWeld - "Next level" DIY battery spot welder
Post by: anishkgt on October 07, 2017, 07:36:09 AM
Well that's good to know. To be honest, the first paragraph was like French to me but I did understand your point.

The second is quite interesting and if it can be developed into bench power supply then I would be interested to buy one from you if your selling it latter as bench PSU itself with mV resolution. That is of course once your done with the kWeld project.


Www.Georgehobby.wordpress.com

Equipments: DSO104z, Hakko FX888D
Title: Re: kWeld - "Next level" DIY battery spot welder
Post by: Fraser on October 23, 2017, 01:03:27 AM
I very recently took delivery of a Tiertime UP! BOX 3D printer (from fellow forum member Toploser).

As part of my 'getting to know the printer' process I have printed various small parts that I needed. I decided to also print the kWeld case as a test of the warping on large area prints. I always print in ABS so warping is a fact of life and needs careful consideration with regard to bed temperature and object placement on the bed.

I told Frank about my intention to produce a test print of his case ad he asked that I share the results with you here.

The result is far from perfect but then I had expected that as I used all default settings without any additional precautions against warping. The print is not a basket case but it did suffer warping at two corners of the raft and this distorted the corners of the case slightly. I will list the issues I discovered with the print below. Some are due to the default print settings, my failure to adequately preheat the build plate, whilst others are likely minor issues with the case design.

1. Case top is printed inverted to avoid masses of support material. This means the top surface will not be as fine a finish as if the case were printed the other way up.

2. When printing objects with a large base area in ABS, there is always the risk of the ABS lifting at the extremities of the print. This is usually countered by pre-heating the bed for at least 15 minutes and printing in a heated chamber. I failed to adequately pre-heat the build plate and chamber ..... oooops  ;D The result was some warping at two corners of the print.

3. The raft in the UP! series printers is usually pretty good when it comes to ease of removal from the object sat on it. The finish on the objects bottom surface is also pretty good. For some reason the raft did not come away easily from some areas of the case top and I was less impressed with the surface of the stepped down area for the LCD and knob. The 'KWeld' logo on the top of the case also presented some issues as it was not easy to remove the support material without leaving obvious tool marks on the plastic below.

4. The Case top design includes a pair of pillars. I tested their strength when formed in ABS. My conclusion is that they are too fragile and easily break away from case top. I believe these pillars would benefit from a thicker wall or a connical shape with a wider base to carry any lateral load.

I attach pictures of the printer and the parts it produced.

Fraser
Title: Re: kWeld - "Next level" DIY battery spot welder
Post by: Fraser on October 23, 2017, 01:05:14 AM
Pictures continued.....

(Including broken pillar detail)
Title: Re: kWeld - "Next level" DIY battery spot welder
Post by: Fraser on October 23, 2017, 01:15:02 AM
A picture of the excellent UP! BOX unit and some pictures of another part I just printed.

Of significance about this part is that it was printed in the vertical plane rather than horizontal where ABS warping can be an issue.
I am going to try printing the kWeld case in the vertical plane next to see how it comes out. The raft will attach at the rear so any surface blemishes are out of sight. The print will take 5 hours so may not get done until a bit later, or tomorrow.

I should state that one of the advantages of printing in ABS is that it can be sanded, filled and painted with modelling products, just like an Airfix model kit  :)  I may sand and paint my kWeld case when I have a good print of it. The Kermet Green is just some UP! Fila that I found at half price ! Not everyones choice of colour me thinks  ;D

Fraser
Title: Re: kWeld - "Next level" DIY battery spot welder
Post by: Fraser on October 24, 2017, 12:49:11 AM
Well the vertical print of the case is under way. Should be finished around 6pm.

It uses a lot of support structure for obvious reasons. The total amount of ABS used is 62g. The conventional inverted flat print uses just over 50g so the additional support material is around 12g. Worth it if the finished product is of good quality though. The ABS filament I am using is genuine higher temperature Tiertime UP! FILA that cost me £10 per 500g reel.

For info, on this print I carried out the correct pre-heat procedure and rotated the object so that the most dense area is facing away from the printers air circulation filter fan. I am wondering if the air flow towards the filter intake on the left hand side encourages faster cooling and shrinkage of the ABS on that side. It is all a learning curve on this new printer. If the print fails, no matter, I will have tried a different approach and discovered its limitations.

Fraser
Title: Re: kWeld - "Next level" DIY battery spot welder
Post by: tatus1969 on October 24, 2017, 01:09:00 AM
4. The Case top design includes a pair of pillars. I tested their strength when formed in ABS. My conclusion is that they are too fragile and easily break away from case top. I believe these pillars would benefit from a thicker wall or a connical shape with a wider base to carry any lateral load.
I'll add that to the improvement list, thanks!
Title: Re: kWeld - "Next level" DIY battery spot welder
Post by: Fraser on October 24, 2017, 02:02:55 AM
Frank,

So far that is the only design issue I have found with the case. It is looking good in the printer at the moment. It is like waiting for a baby to be born :)

Fraser
Title: Re: kWeld - "Next level" DIY battery spot welder
Post by: Fraser on October 24, 2017, 02:10:27 AM
Frank,

I forgot to ask, what design software did you use to create your case please ?

Best Wishes

Fraser
Title: Re: kWeld - "Next level" DIY battery spot welder
Post by: Fraser on October 24, 2017, 03:27:04 AM
The print is almost done....... it looks OK with just a little warping in the front right corner. I have made a major error though. It made me laugh when I noticed. See if you can spot the error :). 5 hours print time wasted  ;D  It is all good experience  :-+

Fraser

Title: Re: kWeld - "Next level" DIY battery spot welder
Post by: tatus1969 on October 24, 2017, 04:49:18 AM
what design software did you use to create your case please ?
Done with Sketchup :-)
Title: Re: kWeld - "Next level" DIY battery spot welder
Post by: tatus1969 on October 24, 2017, 04:57:03 AM
The print is almost done....... it looks OK with just a little warping in the front right corner. I have made a major error though. It made me laugh when I noticed. See if you can spot the error :). 5 hours print time wasted  ;D  It is all good experience  :-+
Took me some time... Mirrored :palm:  :o
Title: Re: kWeld - "Next level" DIY battery spot welder
Post by: Fraser on October 24, 2017, 05:00:18 AM
Frank,

Yes a real  :palm: moment .... no, make that a  :palm: :palm:  ;D

I stupidly mirrored instead of rotated 180 Degrees !

Lesson learnt  ;D

Fraser
Title: Re: kWeld - "Next level" DIY battery spot welder
Post by: Fraser on October 24, 2017, 05:15:20 AM
The case print has completed  :)

We already know it is scrap but I can learn from it and see how well the idea of vertical printing worked.

I am actually pretty pleased with the quality of print produced. The finish is very nice with only the rear panel showing the usual evidence of its attachment to the raft. Such may easily be tidied up and polished if it is an issue.

Sadly there is still an unacceptable amount of warping along the length of the rear panel where it was mounted on the raft. Such is a common issue with printing in ABS. The print bed is currently operating at 90C. Some experienced 3D ABS printers suggest 110C and I will experiment at that temperature.

Pictures of the print followed. There was a lot of support material but it came away very easily and I have no issues with that part of the print process. It worked very well indeed.

I placed the first print attempt next to the latest and I note that the latest print looks darker in colour even though it is the same ABS filament. I prefer that colour and the finish on the surface. No problems with the KWeld Logo this time.

Fraser
Title: Re: kWeld - "Next level" DIY battery spot welder
Post by: Fraser on October 24, 2017, 05:17:26 AM
Pictures continued.....
Title: Re: kWeld - "Next level" DIY battery spot welder
Post by: Fraser on October 24, 2017, 05:19:23 AM
Pictures continued.....
Title: Re: kWeld - "Next level" DIY battery spot welder
Post by: Fraser on October 24, 2017, 05:20:51 AM
Pictures continued....
Title: Re: kWeld - "Next level" DIY battery spot welder
Post by: tatus1969 on October 26, 2017, 10:40:52 PM
and does it fit? I'm curious.
Title: Re: kWeld - "Next level" DIY battery spot welder
Post by: Fraser on October 26, 2017, 11:30:42 PM
I will check.

I can confirm that my UP! BOX printer manages to produce very accurate prints. I needed a plastic sleeve to fit snuggly around a bolt and to have a sliding fit into a tube. I used the dimensions taken from my digital caliper and the resulting 50mm long sleeve was a perfect fit, both on the 6mm bolt and inside the 10.5mm diameter tube. The UP! Software automatically compensates for ABS shrinkage after cooling :)

Fraser
Title: Re: kWeld - "Next level" DIY battery spot welder
Post by: zucca on October 27, 2017, 12:21:02 AM
Thanks tatus1969, read everything in 3 hours or so. Understood almost 30% of it.
Just post it in the Buy/Sell when the next batch is ready.

 ;)

EDIT: Just signed up to your newsletter.
EDIT2: You may want to edit your first post in this thread, new people like me will find quickly what the current status is. For example:
http://www.eevblog.com/forum/projects/diy-programmable-dual-channel-bench-psu-0-50v3a/msg589395/#msg589395 (http://www.eevblog.com/forum/projects/diy-programmable-dual-channel-bench-psu-0-50v3a/msg589395/#msg589395)

Thanks!
Title: Re: kWeld - "Next level" DIY battery spot welder
Post by: tatus1969 on October 28, 2017, 08:12:17 PM
edit your first post in this thread
Thanks for your suggestions! I will do this in a few days. I am almost done with ordering 100x rev3 boards, almost everything else has already arrived.

Maybe a little sneak preview: I could again simplify the production process of the electrode system. This is now the fourth iteration, and I am quite happy with that:

(http://www.eevblog.com/forum/projects/guesses-on-what-i-am-attempting-here/?action=dlattach;attach=364799)
Title: Re: kWeld - "Next level" DIY battery spot welder
Post by: Fraser on October 28, 2017, 09:31:42 PM
That is how I intend to make my probes as well. Easily removable, yet low resistance. You have done a very nice job of those probes :)

Fraser
Title: Re: kWeld - "Next level" DIY battery spot welder
Post by: Kjelt on October 29, 2017, 01:17:45 AM
Maybe a little sneak preview: I could again simplify the production process of the electrode system. This is now the fourth iteration, and I am quite happy with that:
That looks really good, almost resembles a bullet  ;D Is that brass with a copper electrode ?
In the mean time my project has come to a standstill, I am awaiting the final results of which supercaps I need to succesfully weld the tabs, is there already a final outcome?
And my 45V/70A PSU has a major issues, which I am still trying to solve, it is still open for repair.

But I did do some new stuff, I build a jig that will help me do some other welding operation: weld two tabs together, for which I need a vertical welding jig.
So this is how that looks, I found most parts of that jig in the dumpster a few years ago and now have a good use for it.
The electrodes I got where 7mm copper bars for the staggering price of €1.- a piece at my local ironscrap yard  :-+
On top there is a 6mm thread to mount the weldingwire and the bottom is a 5mm tapped hole for your 5mm electrodes I bought from you with the kit.
Title: Re: kWeld - "Next level" DIY battery spot welder
Post by: Fraser on October 29, 2017, 02:28:30 AM
At Franks request I just checked the 3D printed case for fit around the kWeld PCB. I have not printed the final top and bottom pieces but the test piece appears to fit the PCB well. Pictures attached.

I am also intending to make some simple re-enforcement 'washers' for the bases of the two fragile pillars. The rings will be glued in place to provide lateral support. The test piece shown here is just that, an ABS pillar with a snug fit thick ABS washer at its base. I have left the build raft in place for now. The washer will be glued in pace with ABS cement or plastic weld.

I do not have the original Sketchup file so cannot edit the original design.

Fraser

Title: Re: kWeld - "Next level" DIY battery spot welder
Post by: tatus1969 on October 29, 2017, 09:51:15 PM
That looks really good, almost resembles a bullet  ;D Is that brass with a copper electrode ?
Yes, these are 5mm copper rods, crimped to XT150 male "bullets". The electrode holder is CNC machined to fit AWG8 on the other end. Just two crimps to finish everything, one minute of work :-)

In the mean time my project has come to a standstill, I am awaiting the final results of which supercaps I need to succesfully weld the tabs, is there already a final outcome?
And my 45V/70A PSU has a major issues, which I am still trying to solve, it is still open for repair.
After having finished the second kWeld batch, I will go forward with a 2S2P 3S2P BCAP0310-P270-T10 configuration. That has already shown to deliver >1000A in my lab. Your 70A PSU will be perfect for them. The kWeld rev.3 will have an input voltage range from 4V to 30V (SEPIC converter) and will be able to run directly from these capacitors. I have also substantially improved the power switch, I have just made an explicit overload test of the power switch. It is rated at 2000A, and I tested it with 1000 successful pulses at 2200A, followed with 800 pulses at an extreme overload of 2800A (!) before it broke down. Also the inductive kickback handling should be better now, I will test that today.

But I did do some new stuff, I build a jig that will help me do some other welding operation: weld two tabs together, for which I need a vertical welding jig.
So this is how that looks, I found most parts of that jig in the dumpster a few years ago and now have a good use for it.
The electrodes I got where 7mm copper bars for the staggering price of €1.- a piece at my local ironscrap yard  :-+
On top there is a 6mm thread to mount the weldingwire and the bottom is a 5mm tapped hole for your 5mm electrodes I bought from you with the kit.
:-+
Title: Re: kWeld - "Next level" DIY battery spot welder
Post by: beduino on October 29, 2017, 11:59:23 PM
I have also substantially improved the power switch, I have just tested it with 1000 pulses at 2200A, followed with 800 pulses at 2800A (!) before it broke down. Also the inductive kickback handling should be better now, I will test that today.
Old school transformer 230VAC -> 2.5V which means at 10A at primary pulse 1000A on secondary few turns of copper pipe with simple SCR based switch on transformer primary to turnoff at zero crossing much more reliable, however copper costs and transformer weightw, anyway some people buy gold for savings, the more copper we have the richer we are and forget about stuff like this-this is good for selling - lower weight etc, but less copper means lower weight means less reliable lower quality.

High quality products might weight while made of pure metals not plastic crap ;)
Title: Re: kWeld - "Next level" DIY battery spot welder
Post by: tatus1969 on October 30, 2017, 03:43:09 AM
Old school transformer 230VAC -> 2.5V which means at 10A at primary pulse 1000A on secondary few turns of copper pipe with simple SCR based switch on transformer primary to turnoff at zero crossing much more reliable, however copper costs and transformer weightw, anyway some people buy gold for savings, the more copper we have the richer we are and forget about stuff like this-this is good for selling - lower weight etc, but less copper means lower weight means less reliable lower quality.
That will only allow to chop the pulse duration into multiples of 10(8.3)ms, which was too much of a drawback for me when starting this. The kWeld has a resolution of 10us and a minimum pulse width of 40us, which gives it the bandwidth to weld 0.3mm nickel strips equally well as thin copper strands.
Title: Re: kWeld - "Next level" DIY battery spot welder
Post by: Kjelt on October 30, 2017, 04:56:00 AM
After having finished the second kWeld batch, I will go forward with a 2S2P 3S2P BCAP0310-P270-T10 configuration.
Thanks. Where do you get the supercap protection pcb's ? Or did you design them your self ?

Quote
I have also substantially improved the power switch, I have just tested it with 1000 pulses at 2200A, followed with 800 pulses at 2800A (!) before it broke down.

Please remind me, are you talking about the powermosfets on the pcb or something else? What made it break down, overheating? If I only use it once in awhile for ten welds this is not an issue is it?
Title: Re: kWeld - "Next level" DIY battery spot welder
Post by: tatus1969 on October 30, 2017, 10:13:34 AM
Thanks. Where do you get the supercap protection pcb's ? Or did you design them your self ?
I am using them "free air" for now, manually balancing the voltages. I will design a protection PCB soon.

Please remind me, are you talking about the powermosfets on the pcb or something else? What made it break down, overheating? If I only use it once in awhile for ten welds this is not an issue is it?
Yes, it is the MOSFETs blowing up in an extreme overload stress test. Keep in mind that 2800A is 800A above the overcurrent protection (I have disabled it for the test), and power dissipation wise it is twice the maximum (resistive losses are current squared). For the test, I was running the unit directly shorted and had two batteries connected in parallel. This is far from reality, but I wanted to find the limits. Nothing to worry :-)

(http://www.eevblog.com/forum/projects/guesses-on-what-i-am-attempting-here/?action=dlattach;attach=365365)
Title: Re: kWeld - "Next level" DIY battery spot welder
Post by: beduino on October 30, 2017, 07:32:48 PM
For the test, I was running the unit directly shorted and had two batteries connected in parallel. This is far from reality, but I wanted to find the limits.
I can't see any supercaps there - anyway I do not think they are rated for 1000A or so to use them for discharge at such extreme conditions, but while I haven't seen their specs or maybe plenty of them they are used in parallel . lets say 10 each rated at 100A discharge ?

I've already seen another project some time ago where someone used bulky IGBT to switch currents at range of 1000A at spot welder at he was not able to manage induction spikes which kiled many not cheap IGBTs, so what can I say, good luck  :-BROKE
Title: Re: kWeld - "Next level" DIY battery spot welder
Post by: tautech on October 30, 2017, 08:09:16 PM
I've already seen another project some time ago where someone used bulky IGBT to switch currents at range of 1000A at spot welder at he was not able to manage induction spikes which kiled many not cheap IGBTs, so what can I say, good luck  :-BROKE
You need read this thread from the start, all this has been taken care of to reach a commercial product.

It's not at all unreasonable that tatus1969 would want to do destructive tests to push his product to a new level or just make it more robust.
Title: Re: kWeld - "Next level" DIY battery spot welder
Post by: Kjelt on October 30, 2017, 08:46:53 PM
I will design a protection PCB soon.
Great!  :-+ Also hopefully sell them ?

Quote
Yes, it is the MOSFETs blowing up in an extreme overload stress test.
For the test, I was running the unit directly shorted and had two batteries connected in parallel. This is far from reality, but I wanted to find the limits. Nothing to worry :-)
:-+ I think it would be good to explicitly mention this in the start of such posts before potential customers might think there is a liftetime limit or other limitation.
Great to hear that the design is so robust (made in Germany  :-+ )
Title: Re: kWeld - "Next level" DIY battery spot welder
Post by: tatus1969 on October 31, 2017, 01:22:54 AM
I can't see any supercaps there - anyway I do not think they are rated for 1000A or so to use them for discharge at such extreme conditions, but while I haven't seen their specs or maybe plenty of them they are used in parallel . lets say 10 each rated at 100A discharge ?
Maxwell specifies a continuous discharge current of 250A and a short circuit current of 1200A, with a side note "Current possible with short circuit from rated voltage. Do not use as an operating current." They do not specify a maximum pulse current, which leads me to the assumption that these parts are basically thermally limited. I will do a long term test to validate this, but I am very optimistic. They do not show any measurable effect in ESR or capacitance after a few hundred 900A pulses.


Great!  :-+ Also hopefully sell them ?
That's the plan!

:-+ I think it would be good to explicitly mention this in the start of such posts before potential customers might think there is a liftetime limit or other limitation.
Great to hear that the design is so robust (made in Germany  :-+ )
Thanks :-) I noticed this after your post, and have just edited my post above. I am doing destrutive tests because I am preparing for a batch of 100 and do not want to sit here all day repairing units. I didn't mention that I did this destructive test at 4 pulses per second (!) 8)

The last test yesterday was high inductive load at 2200A and it also survived this 1000 times without damage, although I had to reduce the firing rate to once every two seconds to limit heating of the TVS diode. Here is a picture... (The small ugly board left to the kWeld is the new internal 3-40V power supply that was receiving all that inductive spiking, and it keeps all its voltages well within their limits - should be rock stable now.)

(http://www.eevblog.com/forum/projects/guesses-on-what-i-am-attempting-here/?action=dlattach;attach=365559)
Title: Re: kWeld - "Next level" DIY battery spot welder
Post by: beduino on October 31, 2017, 04:17:54 AM
I can't see any supercaps there - anyway I do not think they are rated for 1000A or so to use them for discharge at such extreme conditions, but while I haven't seen their specs or maybe plenty of them they are used in parallel . lets say 10 each rated at 100A discharge ?
Maxwell specifies a continuous discharge current of 250A and a short circuit current of 1200A, with a side note "Current possible with short circuit from rated voltage. Do not use as an operating current." They do not specify a maximum pulse current, which leads me to the assumption that these parts are basically thermally limited. I will do a long term test to validate this, but I am very optimistic. They do not show any measurable effect in ESR or capacitance after a few hundred 900A pulses.
We are talking about this Maxwell HC series ultracapacitors? http://www.mouser.com/ds/2/257/Maxwell_HCSeries_DS_1013793-9-1179788.pdfhttp://www.mouser.com/ds/2/257/Maxwell_HCSeries_DS_1013793-9-1179788.pdf (http://www.mouser.com/ds/2/257/Maxwell_HCSeries_DS_1013793-9-1179788.pdfhttp://www.mouser.com/ds/2/257/Maxwell_HCSeries_DS_1013793-9-1179788.pdf)

On page 4 in  PDF linked above we have BCAP0150 with short circuit 190A BUT: this is in Safety section, and probably you are reading its datasheet in wrong way, since this rating in this section as short circuit only means that in the case of some hazards one can expect such huge discharge current and for example part of PCB can disapear, BUT tread again side note second part: "Do not use as an operating current." which means... those caps are not designed to make short circuits at regular basis at such huge currents, while probably overheats them and when you look carefully at thermal cycles at higher temperatures you have 1000 pulses or so in comparision to comfort temperature usage at 25*C with 10 years life span.

A few hundred 1000A pules is nothing for spot welder ... at 50Hz AC with transformer based spot welder is is less than ... 20 s (seconds) of welding with adjustable pulse energy based on time offset between zero crossing and choosen delay  :palm:

(http://www.eevblog.com/forum/index.php?action=dlattach;topic=90086.0;attach=365643;image)

Could you give us link to datasheet of these upltracaps you are testing? I can't find any Maxwell rated at continous 250A discharge rate....

Bedu.
Title: Re: kWeld - "Next level" DIY battery spot welder
Post by: Southerner on October 31, 2017, 04:50:14 AM
What about using some boostcaps?  Something like these:
http://www.goldmine-elec-products.com/prodinfo.asp?number=G17930 (http://www.goldmine-elec-products.com/prodinfo.asp?number=G17930)
http://www.goldmine-elec-products.com/prodinfo.asp?number=G22499 (http://www.goldmine-elec-products.com/prodinfo.asp?number=G22499)
They look expensive but might work if enough seriesed or one with voltage rating for the lithium battery used.  Another possibility would be the multi farad automotive audio capacitors that used to be so popular for teeth jarring bass automotive audio systems.
Title: Re: kWeld - "Next level" DIY battery spot welder
Post by: ovnr on October 31, 2017, 04:51:18 AM
A few hundred 1000A pules is nothing for spot welder ... at 50Hz AC with transformer based spot welder is is less than ... 20 s (seconds) of welding with adjustable pulse energy based on time offset between zero crossing and choosen delay  :palm:

To be honest: This is a hobbyist-level product. I don't think tatus1969 plans to sell these to battery pack manufacturers. And if you like transformer-based spot welders so much, go buy or build one?

I want something small, reasonably cheap and controllable. Transformer-based options only tick one of those boxes.
Title: Re: kWeld - "Next level" DIY battery spot welder
Post by: ovnr on October 31, 2017, 04:54:18 AM
What about using some boostcaps?  Something like these:
http://www.goldmine-elec-products.com/prodinfo.asp?number=G17930 (http://www.goldmine-elec-products.com/prodinfo.asp?number=G17930)
http://www.goldmine-elec-products.com/prodinfo.asp?number=G22499 (http://www.goldmine-elec-products.com/prodinfo.asp?number=G22499)
They look expensive but might work if enough seriesed or one with voltage rating for the lithium battery used.  Another possibility would be the multi farad automotive audio capacitors that used to be so popular for teeth jarring bass automotive audio systems.

Well, the original design calls for 6x BCAP0310-P270-T10 at $12.17/pop @ Digikey, or $73 total. Since the design is for a 3S2P pack, you'd need at least 3 of the (used!) $45 caps, for a total of $135. Almost twice as much.
Title: Re: kWeld - "Next level" DIY battery spot welder
Post by: Kjelt on October 31, 2017, 09:19:39 AM
Could you give us link to datasheet of these upltracaps you are testing? I can't find any Maxwell rated at continous 250A discharge rate....
He is talking about the bcap 0310 which is cheap and does not have to survive years
http://www.mouser.com/ds/2/257/Maxwell_BCSeries_DS_1017105-4-1179684.pdf (http://www.mouser.com/ds/2/257/Maxwell_BCSeries_DS_1017105-4-1179684.pdf)

If you want more like 2500A buy the 3400:
http://www.mouser.com/ds/2/257/Maxwell_Technologies_k2_2_85v_ds_3000619en_1-1179621.pdf (http://www.mouser.com/ds/2/257/Maxwell_Technologies_k2_2_85v_ds_3000619en_1-1179621.pdf)

Maybe, you do not remember what happened about 75 years ago - hopefully, not everything made by Germany was good:
:palm: i remember well since my family had some real tragedies in that period but as you said that was 75 years ago, over and forgotten and that has nothing to do with the life we are living today and the generations that are living today. I find it rvery offensive that you bring something like this up on an electronics forum.
Title: Re: kWeld - "Next level" DIY battery spot welder
Post by: Simon on October 31, 2017, 09:37:50 AM
Great to hear that the design is so robust (made in Germany  :-+ )

Maybe, you do not remember what happened about 75 years ago - hopefully, not everything made by Germany was good:

Polish 303 Squadron - Battle of Britain
http://www.youtube.com/watch?v=7XleyGF16lM (http://www.youtube.com/watch?v=7XleyGF16lM)

"Squadron 303 (Dywizjon 303) RAF No. 303 "Ko?ciuszko" Polish Fighter Squadron (Polish: Warszawski Dywizjon im. Tadeusza Ko?ciuszki) was the highest-scoring allied unit in the Battle of Britain.[1] It was formed in Britain as part of an agreement between the Polish Government in Exile and the United Kingdom. ..."



There is no relevance in that to this discussion, please stay on topic.
Title: Re: kWeld - &quot;Next level&quot; DIY battery spot welder
Post by: anishkgt on October 31, 2017, 06:35:22 PM
A few hundred 1000A pules is nothing for spot welder ... at 50Hz AC with transformer based spot welder is is less than ... 20 s (seconds) of welding with adjustable pulse energy based on time offset between zero crossing and choosen delay  :palm:

To be honest: This is a hobbyist-level product. I don't think tatus1969 plans to sell these to battery pack manufacturers. And if you like transformer-based spot welders so much, go buy or build one?

I want something small, reasonably cheap and controllable. Transformer-based options only tick one of those boxes.
Or better buy this pcb only  https://rover.ebay.com/rover/0/0/0?mpre=https%3A%2F%2Fwww.ebay.com%2Fulk%2Fitm%2F282466833886 (https://rover.ebay.com/rover/0/0/0?mpre=https%3A%2F%2Fwww.ebay.com%2Fulk%2Fitm%2F282466833886)


Www.Georgehobby.wordpress.com

Equipments: DSO104z, Hakko FX888D, Brymen BM869s
Title: Re: kWeld - "Next level" DIY battery spot welder
Post by: tatus1969 on November 04, 2017, 05:25:24 AM
I am happy to announce that the next batch of kWeld is in production. I accept pre-orders through my shop: https://www.kicksurfer.de/index.php/product-category/kspot-welder-kit/ (https://www.kicksurfer.de/index.php/product-category/kspot-welder-kit/)  All pre-order products are on sale with a 10% discount until Nov 30!

New major features in revision 3:
• replaceable electrode system with minimum assembly effort
• extended input voltage range from 4V to 30V allowing the use of ultracapacitors without an auxiliary power supply
• improved protection against inductive kickback of both power switch and voltage regulator, tested to survive currents in excess of 2500A
• enhanced user interface featuring a rotary encoder with push button

Cheers
Frank
Title: Re: kWeld - "Next level" DIY battery spot welder
Post by: Leo Bodnar on November 04, 2017, 05:44:49 AM
(http://www.eevblog.com/forum/projects/guesses-on-what-i-am-attempting-here/?action=dlattach;attach=365559)
This is one funny looking j-link.  Did Segger change the design recently?
Leo
Title: Re: kWeld - "Next level" DIY battery spot welder
Post by: Fraser on November 04, 2017, 05:45:58 AM
Hi Frank,

Is there any chance of an upgrade kit to add the push button rotary encoder and additional kickback protection to the MK1 unit please. I do not need the broader range regulator though. It would, of course require some reworking of the PCB by me, but that is no problem. New firmware would also be needed but I have your programming cable already.

It would be great to be able to update the Mk1 to at least the essential parts of the Mk2 design.

Fraser
Title: Re: kWeld - "Next level" DIY battery spot welder
Post by: tatus1969 on November 04, 2017, 06:01:48 AM
Is there any chance of an upgrade kit to add the push button rotary encoder and additional kickback protection to the MK1 unit please. I do not need the broader range regulator though. It would, of course require some reworking of the PCB by me, but that is no problem. New firmware would also be needed but I have your programming cable already.
That is possible. Here is a picture of the additional protection elements. All parts are available at Digikey:
SLD8S28A (large 28V TVS, Littelfuse)
SMDJ28A (28V TVS in SMC package, Littelfuse)
2920L030 (resettable PTC fuse, 300mA, Littelfuse)

The first one is new, and it goes in parallel to the MOSFETs. The other two replace the "quick fix" that I recommended before. I didn't like the resistor in the current path, that fuse also adds resistance.

The rotary encoder is not that simple, because it uses new microcontroller pins and has a different footprint. If you still want to do this, the part no. is PEC12R-4220F-S0024 (also Digikey). I have attached the relevant schematic diagram page here as well.
Title: Re: kWeld - "Next level" DIY battery spot welder
Post by: Fraser on November 04, 2017, 06:15:11 AM
Thanks Frank,

That does not look too hard to achieve :) I will order the parts.
Thank you for the schematic. Will you make the new firmware available as well at some point in time please ?

Best Wishes

Fraser
Title: Re: kWeld - "Next level" DIY battery spot welder
Post by: tatus1969 on November 04, 2017, 10:34:35 AM
Will you make the new firmware available as well at some point in time please ?
Yes of course :-) Otherwise the firmware update dongle would not make much sense ;-) I plan a kWeld product page that will contain links to available firmware versions together with the revision history.
Title: Re: kWeld - "Next level" DIY battery spot welder
Post by: tatus1969 on November 04, 2017, 11:41:46 PM
This is one funny looking j-link.  Did Segger change the design recently?
Leo
That is an older version I got long ago from ebay. Hopefully not a clone?
Title: Re: kWeld - "Next level" DIY battery spot welder
Post by: Fraser on November 05, 2017, 12:41:28 AM
Frank,

I have received the V2 to V3 upgrade information pack.

Thank you so much for going to the trouble of producing such a detailed document with such excellent pictures. I had not realised that the MOSFET drive had also increased.

Best Wishes

Fraser
Title: Re: kWeld - "Next level" DIY battery spot welder
Post by: tatus1969 on November 05, 2017, 01:00:32 AM
I have received the V2 to V3 upgrade information pack.

Thank you so much for going to the trouble of producing such a detailed document with such excellent pictures. I had not realised that the MOSFET drive had also increased.
No problem, you're welcome! Less than 2hrs of work.

Yes, I forgot to mention the MOSFET drive improvement. I realized that this was necessary when going the route towards 2800A. With the standard configuration and the recommended Turnigy it is not necessary because the current is "only" 1400A, but it doesn't even increase the kit price. I was afraid of excessive ringing from overly fast switching at the very beginning, but that has proven not to be problematic at all.

The inductive spiking countermeasures have the same rationale. The rev2 has no problem without it at 1400A, but I expect that many people will have their own and more powerful source. I had one customer who wasn't able to calibrate the unit. It turned out that this was due to the overcurrent protection constantly tripping.

I have attached the manual here for everybody. I would be willing to make a group purchase of the necessary components, just send me a PM. I will also make the entire upgrade free of charge, I would just want to have the shipping paid.

UPDATE: the parts are 7.78€ per set, so I would need at least 7 requests to get above Digikey's free shipping threshold. I will ship in simple envelopes for 0.90€.
Title: Re: kWeld - "Next level" DIY battery spot welder
Post by: Fraser on November 05, 2017, 01:32:04 AM
Frank,

What a very kind offer.

I personally will happily pay for the parts.

PM on its way :)

Best Wishes

Fraser
Title: Re: kWeld - "Next level" DIY battery spot welder
Post by: Leo Bodnar on November 05, 2017, 03:28:13 AM
This is one funny looking j-link.  Did Segger change the design recently?
Leo
That is an older version I got long ago from ebay. Hopefully not a clone?
Looks totally legit.
Title: Re: kWeld - "Next level" DIY battery spot welder
Post by: eKretz on November 19, 2017, 10:26:17 AM
Pre-orders are already all sold out, eh?
Title: Re: kWeld - "Next level" DIY battery spot welder
Post by: tatus1969 on November 19, 2017, 10:11:15 PM
Pre-orders are already all sold out, eh?
I apparently underestimated the demand, and ran out of stock by just pre-orders in less than a week. I plan another batch right after having received the current one. I'll inform again through the newsletter. But in order help me estimate the demand, I have just implemented an "inform me on availability" button for the sold out products that puts you on a waiting list when you click it.
Title: Re: kWeld - "Next level" DIY battery spot welder
Post by: Derriell on November 25, 2017, 08:26:22 AM
What is the recommended internal resistance of a 2S LiPo battery pack for max 1500A?

Is my following calculation correct?

Given 2S LiPo, lets say at 4V per cell, giving room for 2*1V voltage decrease during load in order not to undervolt the cells.

2V/1500A = 1.3mOhm for the whole pack  => 0.66mOhm per cell

Or do the LiPos behave differently than a normal resistor under load?

Thank you
Title: Re: kWeld - "Next level" DIY battery spot welder
Post by: tatus1969 on November 25, 2017, 08:39:35 PM
What is the recommended internal resistance of a 2S LiPo battery pack for max 1500A?

Is my following calculation correct?

Given 2S LiPo, lets say at 4V per cell, giving room for 2*1V voltage decrease during load in order not to undervolt the cells.

2V/1500A = 1.3mOhm for the whole pack  => 0.66mOhm per cell

Or do the LiPos behave differently than a normal resistor under load?

Thank you
The calculation goes a different way. You calculate the current that the battery delivers when it is being short circuited by the welder. Welder and (stock) cables contribute approx 2.4 milliOhm, a typical resistance of the weld spot itself is 1 milliOhm. current = lipo_pack_open_circuit_voltage / (3.4 milliOhm + lipo_pack_resistance).

You don't need to worry about undervolting the battery when using it like this, that voltage is related to the chemistry and not to the output voltage under load. You should respect the output current capacity of the pack though, as standard 50C packs get damaged from the high current. So far only the ultra high current packs like Turnigy nanotech or graphite have been tested to be considerably robust. But respect the three golden Lipo rules anyway: a) only operate them with great caution, b) store them in a fire safe place when not using them, and c) charge them under supervision only.
Title: Re: kWeld - "Next level" DIY battery spot welder
Post by: Derriell on November 27, 2017, 10:14:03 PM
Ah yes, thank you! This means, if I want 1500A I need a 2S battery  pack (8V) with:

8V/1500A - 3.4mOhm = ~ 2mOhm
Title: Re: kWeld - "Next level" DIY battery spot welder
Post by: tatus1969 on November 28, 2017, 09:01:47 PM
Ah yes, thank you! This means, if I want 1500A I need a 2S battery  pack (8V) with:

8V/1500A - 3.4mOhm = ~ 2mOhm
exactly!
Title: Re: kWeld - "Next level" DIY battery spot welder
Post by: Derriell on December 04, 2017, 12:12:42 AM
A 2S6P pack with the new Samsung SDI INR21700-30T cells with just 10mOhm is good for around 1000A welding power. I find them even more interesting to make nice and power full battery packs  :-+ If you get them for 5$ per cell that makes it 60$.

Test:
http://www.dampfakkus.de/akkutest.php?id=673 (http://www.dampfakkus.de/akkutest.php?id=673)
https://www.e-cigarette-forum.com/threads/samsung-inr21700-30t-35a-3000mah-21700-bench-test-results-an-incredible-40a-3100mah-battery.798683/ (https://www.e-cigarette-forum.com/threads/samsung-inr21700-30t-35a-3000mah-21700-bench-test-results-an-incredible-40a-3100mah-battery.798683/)

I'm not sure about the power source yet though. I might as well just use several 3S RC-LiPos with 4mm gold connector in parallel for the welding. When I weld I can't fly anyway  ;) 4-6 3S packs should do the jobs just fine with an adapter cable. But a problem with this seems to be that every time I want to weld I need to charge the batteries to the same voltage and if I want to store them later I need to discharge them a bit.
Title: Re: kWeld - "Next level" DIY battery spot welder
Post by: tatus1969 on December 04, 2017, 10:04:18 PM
A 2S6P pack with the new Samsung SDI INR21700-30T cells with just 10mOhm is good for around 1000A welding power. I find them even more interesting to make nice and power full battery packs  :-+ If you get them for 5$ per cell that makes it 60$.

Test:
http://www.dampfakkus.de/akkutest.php?id=673 (http://www.dampfakkus.de/akkutest.php?id=673)
https://www.e-cigarette-forum.com/threads/samsung-inr21700-30t-35a-3000mah-21700-bench-test-results-an-incredible-40a-3100mah-battery.798683/ (https://www.e-cigarette-forum.com/threads/samsung-inr21700-30t-35a-3000mah-21700-bench-test-results-an-incredible-40a-3100mah-battery.798683/)

I'm not sure about the power source yet though. I might as well just use several 3S RC-LiPos with 4mm gold connector in parallel for the welding. When I weld I can't fly anyway  ;) 4-6 3S packs should do the jobs just fine with an adapter cable. But a problem with this seems to be that every time I want to weld I need to charge the batteries to the same voltage and if I want to store them later I need to discharge them a bit.
In the calculations, remember to take the total resistance of the welder into account as well. For kWeld, that is around 2.5mOhms. And the weld spot itself accounts for another 0-2mOhms.
Title: Re: kWeld - "Next level" DIY battery spot welder
Post by: tatus1969 on December 04, 2017, 10:32:24 PM
I'm happy to announce the release of kWeld firmware rev2.0. It is backwards compatible with the existing rev2 modules as well the new rev3 ones that are on the way to me.

New features:
- added support for hardware revision 3
- added support for rotary encoder
- added configuration menu
- current limit is now calculated from adjustable cable length
- made auto mode firing delay adjustable
- added adjustable battery undervoltage detection
- improved open circuit detection when welding

The binary can be downloaded from this page:
https://www.kicksurfer.de/index.php/kweld/ (https://www.kicksurfer.de/index.php/kweld/)

For those of you who already have the firmware update tool in hands: I'm sorry but I haven't found the time to include the  update procedure in the operating manual yet. I am busy shipping out the current production batch by the end of this week, and I will update the manuals thereafter.

For now, I only have this short description, if something is not obvious please let me know:
1. Connect the small adapter board to the USB adapter so that the connectors on the adapter are facing up, and the LEDs on the USB adapter are visible (i.e. "natural" position, components on both boards facing up)
2. Connect the assembly to kWeld with the short cable (goes out to the right), use a mini USB cable (not included) to connect to PC, if necessary install drivers (http://www.ftdichip.com/Drivers/VCP.htm (http://www.ftdichip.com/Drivers/VCP.htm))
3. Find the new serial port via Windows Device Manager
4. In extraputty (http://www.extraputty.com/ (http://www.extraputty.com/)), establish a serial connection with this COM port and 115200 / 8N1 / no handshake
5. Power up kWeld, then type in a small "k" in the console
6. Bootloader must respond now
7. Now type a small "y"
8. Now make a YMODEM transfer with the firmware file via the extraputty menu (Files Transfer -> YMODEM -> Send)
9. Wait for the transfer to complete, it should then read an "OK"
10. Now trigger kWeld restart by typing a small "a"

For those who have added the encoder to their kWeld rev2: you need to type "v3" into the console when kWeld is running normal (not in firmware update mode). (There will be no echo.) This enables encoder use. Typing "v2" instead switches back to potentiometer mode. The firmware does a reset in each case and restarts.

Here is a short description of the new configuration menu:
1. for rev2 (potentiometer) systems, turn dial all the way left and press trigger switch to enter the menu // for rev3 (encoder) systems, push the dial know instead
2. turn the knob to choose from one of the available options:
"CAL": enter calibration function (as known)
"Mode": select between manual and auto trigger modes
"TrgDelay": [default 0.5s] adjust trigger delay in auto mode
"DefaultE": [default 10.0J] adjust set energy level after power-on (only when using encoder)
"CableLen": [default 1.0m] enter the total length of the power wiring (add up all conductor segments), the firmware calculates the correct current limit from that (using the inductive kickback formula from the operating manual). This provides correct protection in case you are using longer wires than standard
"LoBatt": [default 0.0V] sets battery warning voltage level (set to 0 if you don't want to use it)
"Exit": leave the menu
Title: Re: kWeld - "Next level" DIY battery spot welder
Post by: Fraser on December 05, 2017, 04:48:17 AM
Excellent work Frank  :-+

I now have a huge incentive to find time to construct my KWeld and upgrade it to V3  :)

A very big 'Thank You'

Fraser
Title: Re: kWeld - "Next level" DIY battery spot welder
Post by: tatus1969 on December 05, 2017, 07:51:49 AM
Excellent work Frank  :-+

I now have a huge incentive to find time to construct my KWeld and upgrade it to V3  :)

A very big 'Thank You'

Fraser
you're welcome :-) Did you receive your upgrade kit already?
Title: Re: kWeld - "Next level" DIY battery spot welder
Post by: Fraser on December 05, 2017, 08:06:38 AM
Hi Frank,

Yes it has just arrived safely and was added to my KWeld project parts box :) Thank you  :-+

Fraser
Title: Re: kWeld - "Next level" DIY battery spot welder
Post by: TopQuark on December 06, 2017, 04:27:01 AM
Hi Frank, newbie here :D I have looked at the schematics you've posted and are very curious about how you measure current through the welder. I see your circuit measuring voltage at the input, out+ and out-. The input fuse and the parallel mosfets does have resistance and allows current to be derived, but are those resistance alone precise and stable enough to be used as a shunt? Or do you measure current with other clever methods? Hope this is not too much of a commercial secret for you to share.  :P

Alex
Title: Re: kWeld - &quot;Next level&quot; DIY battery spot welder
Post by: anishkgt on December 06, 2017, 07:04:03 AM
He has answered it earlier for the same question I had asked. Scroll to page from 1-6 or something if I can recall.


Www.Georgehobby.wordpress.com

Equipments: DSO104z, Hakko FX888D, Brymen BM869s
Title: Re: kWeld - "Next level" DIY battery spot welder
Post by: TopQuark on December 06, 2017, 03:39:48 PM
Not sure I got it correctly or not. So the kWeld determines current draw by measuring voltage drop across the welding cables and electrodes? Does the welder rely on the length and thickness of welding cables used to be the same as those provided by Frank? I apologize if I am asking too much.

To be really honest, I am trying to replicate one for myself to learn electronics. Being a undergraduate freshman who don't have a major yet, I definitely dare not sell my potential product to others, I might even blow up my dorm room in the process of trying to build one :-DD Also I am too broke to buy the real deal from Frank.
Title: Re: kWeld - "Next level" DIY battery spot welder
Post by: tatus1969 on December 06, 2017, 08:52:39 PM
Not sure I got it correctly or not. So the kWeld determines current draw by measuring voltage drop across the welding cables and electrodes? Does the welder rely on the length and thickness of welding cables used to be the same as those provided by Frank? I apologize if I am asking too much.

To be really honest, I am trying to replicate one for myself to learn electronics. Being a undergraduate freshman who don't have a major yet, I definitely dare not sell my potential product to others, I might even blow up my dorm room in the process of trying to build one :-DD Also I am too broke to buy the real deal from Frank.
kWeld is measuring current through the on-state resistance of the MOSFETs, using them as a shunt. This is not very accurate as you suspected, you end up with something in the order of +-30%. And there is quite a temperature coefficient. But absolute accuracy is not that important here, the idea is to have repeatable results. The user will adjust the pulse energy to his needs anyway. The temperature coefficient is more important, and that is one of the reasons why I have chosen the most powerful MOSFETs available (at quite a cost), because they do not heat up much. Even during my torture tests, I never managed to heat them above 50°C.
Title: kWeld - "Next level" DIY battery spot welder
Post by: anishkgt on December 06, 2017, 08:59:04 PM
Well if you want accurate current measurement, one way would be to measure the resistance of the cable via 4 wire method and measure voltage on portion of the cable like 10cm apart then use ohms law to calculate current.

You could add these to the code also.
Hope this helps.


Www.Georgehobby.wordpress.com

Equipments: DSO104z, Hakko FX888D, Brymen BM869s
Title: Re: kWeld - "Next level" DIY battery spot welder
Post by: Fraser on December 06, 2017, 09:13:16 PM
On the matter of current measurement accuracy, I concur with Frank.

It is not necessary to have absolute accuracy of current measurement in a spot welder as there are many variables that can effect such, including the performance and contact area of the probes combined with battery tag strips. What is important is repeatability of weld. Franks design is excellent in this respect because of his novel approach of using Energy measurement rather than just a timer, as found in some other designs.

It would be possible to create a highly accurate current measurement for a spot welder, but one has to ask, is it needed and what advantages does it offer to offset the added complexity of the design ? I would argue that Franks approach is both novel and relatively minimalist for the required task (the KISS principle). The operating principle is well thought through and produces the desired repeatable results   :-+ A far better design than my £80 Chinese spot welder that just uses a transformer and timer controlled triac to set the weld current duration.

Fraser
Title: Re: kWeld - "Next level" DIY battery spot welder
Post by: tatus1969 on December 06, 2017, 09:17:06 PM
Well if you want accurate current measurement, one way would be to measure the resistance of the cable via 4 wire method and measure voltage on portion of the cable like 10cm apart then use ohms law to calculate current.

You could add these to the code also.
Hope this helps.


Www.Georgehobby.wordpress.com (http://Www.Georgehobby.wordpress.com)

Equipments: DSO104z, Hakko FX888D, Brymen BM869s
The tempco of copper is a in the same order as that of a MOSFET (4m / K), but the wiring also heats up much more. So there is no advantage with that respect. The absolute accuracy could be better, but at additional cost and mechanical complexity. This is why i decided against that in the beginning. I also thought of adding a dedicated shunt resistor, but didn't like the additional cost and complexity either.
Title: Re: kWeld - &quot;Next level&quot; DIY battery spot welder
Post by: anishkgt on December 06, 2017, 09:18:26 PM
I wouldn’t argue about franks design but just sharing idea for current measurement.


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Title: Re: kWeld - &quot;Next level&quot; DIY battery spot welder
Post by: anishkgt on December 06, 2017, 09:23:34 PM
Quote
The tempco of copper is a in the same order as that of a MOSFET (4m / K), but the wiring also heats up much more. So there is no advantage with that respect. The absolute accuracy could be better, but at additional cost and mechanical complexity. This is why i decided against that in the beginning. I also thought of adding a dedicated shunt resistor, but didn't like the additional cost and complexity either.

Yes a bit of work too but reading voltage “ 10cm apart” is like using a shunt. Since you also provide the cable too the resistance would be a constant but as mentioned by others “how important is current accuracy?”


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Title: Re: kWeld - &quot;Next level&quot; DIY battery spot welder
Post by: tatus1969 on December 06, 2017, 09:36:00 PM
the resistance would be a constant
No it's not. It is copper, which has a huge temperature coefficient  ;)
Title: Re: kWeld - &quot;Next level&quot; DIY battery spot welder
Post by: anishkgt on December 06, 2017, 09:38:19 PM
Hmmm yea. Oooopsy again that wouldn’t be accurate but would give an idea of it.


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Title: Re: kWeld - &quot;Next level&quot; DIY battery spot welder
Post by: tatus1969 on December 07, 2017, 02:26:09 AM
Hmmm yea. Oooopsy again that wouldn’t be accurate but would give an idea of it.
Nothing that the on-state resistance of the MOSFET's wouldn't give - except better absolute accuracy.
Title: Re: kWeld - "Next level" DIY battery spot welder
Post by: TopQuark on December 07, 2017, 06:36:41 PM
Frank, really appreciate your answer :D using the mosfets as a shunt is quite a clever idea. How about using the fuse as a shunt? Does the resistance of the fuse change much from one to another, or does the temperature rise of the fuse contribute too much to resistance instability?

If I end up building one for myself, my OCD will probably force me to place a 'real' shunt resistor to get a slightly better current reading. Maybe a 100 microOhm resistor with an amplifier circuit similar to what Dave used for the uCurrent project. But now I am quite occupied with another project I have on hand, so maybe I'll just place Frank's welder on the top of my Christmas wishlist... :P
Title: Re: kWeld - "Next level" DIY battery spot welder
Post by: tatus1969 on December 08, 2017, 04:28:05 AM
How about using the fuse as a shunt? Does the resistance of the fuse change much from one to another, or does the temperature rise of the fuse contribute too much to resistance instability?
Both, as I don't always buy the fuses from the same place. And they heat up significantly, way more than the MOSFETs.
Title: Re: kWeld - "Next level" DIY battery spot welder
Post by: JohnG on December 09, 2017, 02:14:48 AM
For what it's worth, I have found that Infineon MOSFETs have pretty accurate resistance values, maybe within 10% or better, and the tempco is well specified. My experience has mostly been 100V FETs and above, so it may not be directly applicable here.

I would guess that if you know the FET temp, you can do a pretty good job. For those who have to know, there could be an option to calibrate the current using an external shunt. Not sure if it would be worthwhile, because I suspect the current varies a lot during the weld process.

John

Title: Re: kWeld - "Next level" DIY battery spot welder
Post by: tatus1969 on December 09, 2017, 10:21:37 AM
For what it's worth, I have found that Infineon MOSFETs have pretty accurate resistance values, maybe within 10% or better, and the tempco is well specified. My experience has mostly been 100V FETs and above, so it may not be directly applicable here.
Did you find this by measuring, or were these datasheet figures?

I would guess that if you know the FET temp, you can do a pretty good job. For those who have to know, there could be an option to calibrate the current using an external shunt. Not sure if it would be worthwhile, because I suspect the current varies a lot during the weld process.
I was considering calibrating Rdson during production testing, but as mentioned before the absolute accuracy is not that important for this application. And as the MOSFETs only heat up by 25K (accounting for ~10% of error), I didn't go for measuring their temperature either. If I would add temperature monitoring, then to protect the power stage in first place.

In the end, kWeld has proven to make very repeatable welding results, and that's all it has to do  ;)
Title: Re: kWeld - "Next level" DIY battery spot welder
Post by: ovnr on December 11, 2017, 12:34:08 AM
In the end, kWeld has proven to make very repeatable welding results, and that's all it has to do  ;)

Let's have a massive round of applause for tatus1969. Congratulations, you've avoided the feature creep hole I invariably spend my days digging even deeper...
Title: Re: kWeld - "Next level" DIY battery spot welder
Post by: Fraser on December 11, 2017, 01:06:46 AM
Yes, the scourge of many projects. Frank has released a perfectly functional design that he is now enhancing in a controlled manner to provide sensible improvement. The wish list for many projects can become a nightmare as the BoM and design man hours can spiral out of control.

Great work Frank  :-+

Fraser
Title: Re: kWeld - "Next level" DIY battery spot welder
Post by: rhb on December 11, 2017, 05:12:55 AM
I went back through the thread quite a bit, but it's a long thread, so please forgive me if this was already addressed.

As I understand it, you're discharging a capacitor bank and you're measuring the energy of the pulse by measuring the current.  The accuracy of the  measurement is limited by the difficulty of measuring a large current under dynamic conditions.

If the charging current is disconnected prior to the pulse and the capacitor bank voltage measured before and after the pulse that should give an accurate measure of the energy from first principles.  There is likely some voltage variation after the pulse is cutoff related to the degree to which the capacitors do not discharge uniformly.  However, this might provide a means for assessing the condition of the capacitor bank.

Is there a problem with using the relationship among capacitance, charge and voltage to determine the energy of a pulse that I have overlooked?  This seems to me a good bit easier and more accurate.  One still has heating losses, but those should not be too hard to measure or estimate using suitably placed thermistors.
Title: Re: kWeld - "Next level" DIY battery spot welder
Post by: JohnG on December 11, 2017, 09:17:54 AM
For what it's worth, I have found that Infineon MOSFETs have pretty accurate resistance values, maybe within 10% or better, and the tempco is well specified. My experience has mostly been 100V FETs and above, so it may not be directly applicable here.
Did you find this by measuring, or were these datasheet figures?



At one point I did (i.e. my tech did) a LOT of voltage drop measurements on Si and SiC MOSFETs and IGBTs at 25, 75, and 125C. The Infineon ones all measured within 10% of that specified in the data sheet. Note that they were easier to measure than high current, low voltage FETs since the Ron was 10s to hundreds of milliohm, but I was surprised at how close they were to the data sheet. Interestingly, so were the measured CV curves.

Not all the FETs were like this... 

John
Title: Re: kWeld - "Next level" DIY battery spot welder
Post by: ovnr on December 11, 2017, 10:02:51 AM
Is there a problem with using the relationship among capacitance, charge and voltage to determine the energy of a pulse that I have overlooked?  This seems to me a good bit easier and more accurate.  One still has heating losses, but those should not be too hard to measure or estimate using suitably placed thermistors.

That only estimates how much energy you drain from the capacitors - not how much gets delivered to the weld site. A majority of the energy consumption is in the capacitors themselves (ESR).

Also, kWeld supports both supercaps and high-energy LiPo cells; the latter are more cost-effective, IMO, and would not work with your proposed measurement method.

Using Rds(on) to estimate current is actually a really common method. In fact, if you're reading this on a computer you're already using a device that does it, namely the CPU core voltage regulator on your motherboard.

Title: Re: kWeld - "Next level" DIY battery spot welder
Post by: rhb on December 11, 2017, 12:18:05 PM
ESR is measurable as is the cable resistance.  The relationship between charge and voltage for a LiPo is more complex than the linear relationship of a capacitor,  but I don't see why it is harder than the time variant  Rds(on) of a MOSFET passing a large current for a short period of time. 

A comparison to the measurement of CPU drains is fatuous at best.  That does not involve going from 0 to 1000A and back in a fraction of a heartbeat.
Title: Re: kWeld - "Next level" DIY battery spot welder
Post by: ovnr on December 11, 2017, 12:58:43 PM
ESR is measurable as is the cable resistance.  The relationship between charge and voltage for a LiPo is more complex than the linear relationship of a capacitor,  but I don't see why it is harder than the time variant  Rds(on) of a MOSFET passing a large current for a short period of time. 
Wait. You think that estimating how many joules - with a precision of 0.1J or better - remain in a LiPo based solely on the pack voltage is easier than Rds(on) sensing? Really? Besides, as tatus1969 has said: The weld energy is not calibrated in any way. You're supposed to find the correct energy level by trial and error, at which point the welder will produce consistent results.

Also, the welder does the joule counting during the welding process, cutting off the current the instant the correct energy level has been reached. That means you can't very well measure the voltage before and after.

A comparison to the measurement of CPU drains is fatuous at best.  That does not involve going from 0 to 1000A and back in a fraction of a heartbeat.
True; 1 kA CPUs are still a bit out. Still, we do have 200+ amp CPUs like AMDs Threadripper (with a healthy overclock). And the VRM switches at 500+ kHz.
Title: Re: kWeld - "Next level" DIY battery spot welder
Post by: tatus1969 on December 11, 2017, 05:54:30 PM
As I understand it, you're discharging a capacitor bank and you're measuring the energy of the pulse by measuring the current.  The accuracy of the  measurement is limited by the difficulty of measuring a large current under dynamic conditions.
The kWeld firmware uses a measurement cycle of 10 microseconds, that is enough bandwidth to sample the current waveform.

If the charging current is disconnected prior to the pulse and the capacitor bank voltage measured before and after the pulse that should give an accurate measure of the energy from first principles.  There is likely some voltage variation after the pulse is cutoff related to the degree to which the capacitors do not discharge uniformly.  However, this might provide a means for assessing the condition of the capacitor bank.
There are quite a few CD welders that use a similar mechanism. But instead of measuring voltage before and after, they let the user dial in the desired stored energy, calculate the corresponding charging voltage for them, and firing all the energy at once until the capacitors are drained completely. This has the advantage that you can use an SCR as the switch, as it does not have to have the capability to interrupt the flowing current again.

Is there a problem with using the relationship among capacitance, charge and voltage to determine the energy of a pulse that I have overlooked?  This seems to me a good bit easier and more accurate.  One still has heating losses, but those should not be too hard to measure or estimate using suitably placed thermistors.
The idea behind kWeld is to control the energy that goes into the weld. (To achieve that, measuring the flowing current is just one requisite.) With your idea (or the way standard CD welders work) you can only control the total energy consumption. A large part of that goes into the capacitor (or battery) itself, the connecting leads, and the switch.
Title: Re: kWeld - "Next level" DIY battery spot welder
Post by: tatus1969 on December 11, 2017, 05:59:08 PM
ESR is measurable as is the cable resistance.
Yes, but measuring ESR is technically easier, as the MOSFET that you use as the current shunt is typically GND referenced. This way you only need to measure one ground referenced voltage, instead of having to measure a voltage differential. In this way I am following the same rationale that has brought up ESR current sensing in DC/DC converters.
Title: Re: kWeld - "Next level" DIY battery spot welder
Post by: rhb on December 12, 2017, 11:44:33 AM
Interesting.  Thanks for the explanation.
Title: Re: kWeld - "Next level" DIY battery spot welder
Post by: carracing111 on January 01, 2018, 04:39:01 AM
Hello everyone.

I am waiting to buy a KWeld spot welder. It has an incredible appearance!

Meanwhile I'm doing some capacitor testing with my Arduino Spot Welder.

I have purchased two Maxwell 58F units to build two different welders and power my Arduino Spot Welder, and I also hope to use them with my future  Kweld !

At the moment I have not obtained any acceptable welding with Maxwell 58F. It seems that the capacitors do not have enough power.
I have charged the capacitors with a small CC CV power supply (12V, 5A).
I have connected the Arduino Spot Welder directly to the capacitors to perform the tests. The set works, but the welds are very loose, the solders hardly leave a mark on the nickel.

The arduino spot welder is working perfectly with a car lead battery.
Of course I have checked that the capacitors have reached their working voltage, 12.15v. I do not understand why even the first weld is not acceptable.

I just made some tests with the same configuration but with 5 car audio capacitors, they are Chinese and of poor quality. In theory it is assumed that 2 parallel capacitors are 1 farad.

With the Chinese capacitors, the Arduino Spot Welder works very well!

(https://preview.ibb.co/hf59bb/20171231_043523.jpg) (https://ibb.co/iDghwb)

(https://preview.ibb.co/nvfVgb/20171231_043607.jpg) (https://ibb.co/kVou7G)

I can not understand why the Maxwell capacitors do not work! I bought them on Mouser and they are not cheap! Can the capacitors be defective?

I have tried both units and the result is just as bad.
Do they need more than 12V to work properly? I can not think of anything else.

I would greatly appreciate any ideas or advice.

Happy New Year !
Title: Re: kWeld - "Next level" DIY battery spot welder
Post by: tatus1969 on January 02, 2018, 12:54:28 AM
I have purchased two Maxwell 58F units to build two different welders and power my Arduino Spot Welder, and I also hope to use them with my future  Kweld !
Happy New Year to you too!

I assume that it is this module:  BMOD0058 E016 B02

A quick look in the datasheet tells that they have 22mOhm ESR. This is way too much for welding. The modules seem to be optimized towards energy density, not power density. If you still want to use them, I would suggest ripping both modules apart and reconfigure them in a 3S4P configuration. That way you'd achieve 2.75mOhm ESR at 5.3V, which should result in 870A weld current with kWeld. That should be good enough for 0.1mm nickel, maybe 0.2mm.
Title: Re: kWeld - "Next level" DIY battery spot welder
Post by: carracing111 on January 02, 2018, 04:10:51 AM
Thank you very much for the reply.

That's right, it's the Maxwell BMOD0058 E016 B02.

I chose these modules inspired by this design: https://www.thingiverse.com/thing:2588371 (https://www.thingiverse.com/thing:2588371)

In the article he says that they work well and that's why I chose them.
These modules are not cheap, If I can not get the spot welder to work with just one module, it might be worth it to return them and order different capacitors ...

In the electrical diagram of the article where these capacitors are used, I have seen that there are 2 resistors of 10ohm and 100W in parallel with the capacitors.

I thought that the purpose of the resistors was only to discharge the capacitors after using the soldering iron. Maybe they are necessary for it to work properly?

I'm sorry, but my knowledge of electronics is still very basic.

Regards.
Title: Re: kWeld - "Next level" DIY battery spot welder
Post by: tatus1969 on January 02, 2018, 04:26:05 AM
this design: https://www.thingiverse.com/thing:2588371 (https://www.thingiverse.com/thing:2588371)
Maybe you contact the author of that unit, he is talking about 0.22mOhm ESR but the datasheet clearly states 22mR. That is a factor 100 off.

In the electrical diagram of the article where these capacitors are used, I have seen that there are 2 resistors of 10ohm and 100W in parallel with the capacitors.
I thought that the purpose of the resistors was only to discharge the capacitors after using the soldering iron. Maybe they are necessary for it to work properly?
Thats not relevant, they are for discharge. Just make sure to use the thickest wires that you can afford. Use AWG8 or better.

I'm sorry, but my knowledge of electronics is still very basic.
Pay attention to what you do, you are dealing with high energies. You can easily hurt yourself or burn down your house if you do not fully understand what you are doing. Also take great care of handling Lithium batteries, they are potentially dangerous.
Title: Re: kWeld - "Next level" DIY battery spot welder
Post by: carracing111 on January 02, 2018, 05:13:43 AM
Thanks, I have contacted the author of the article.

Although I believe that I will return the Maxwell modules and I will obtain the ones you recommend or if you sell them directly.

Regards.
Title: Re: kWeld - "Next level" DIY battery spot welder
Post by: tatus1969 on January 02, 2018, 09:32:34 PM
if you sell them directly.
I am currently working on the next batch kWeld, and on a customer project (a motor controller), so I didn't have time to continue the stationery kWeld power supply. I think that I can continue this in three weeks, as it is already almost mature. I plan to sell the capacitor balancer board with and without capacitors.
Title: Re: kWeld - "Next level" DIY battery spot welder
Post by: tatus1969 on January 02, 2018, 09:36:32 PM
A quick update: I had time to test the Turnigy graphene 3S / 6000mAh / 65C. It delivers about the same current as the smaller and cheaper nanotech 3S / 5000mAh / 65-130C battery. The only weakness is that the leads are only AWG10. Does anyone know of affordable Lipos that have AWG8 and XT150 connectors?
Title: Re: kWeld - "Next level" DIY battery spot welder
Post by: Derriell on January 05, 2018, 05:53:59 AM
It has arrived today   :-+

How many mOhms (approximately) will it lose when using thicker cables and solder the cables (partly) directly to the board?
Title: Re: kWeld - "Next level" DIY battery spot welder
Post by: tatus1969 on January 05, 2018, 09:45:41 PM
It has arrived today   :-+

How many mOhms (approximately) will it lose when using thicker cables and solder the cables (partly) directly to the board?
Great!

You can estimate this directly from the AWG relationship, I use to use Wikipedia. The table is for solid cores, you can add maybe 15% to the numbers for fine stranded cores. https://en.wikipedia.org/wiki/American_wire_gauge

The standard setup is AWG8, total length 0.8m.

I don't recommend soldering the excess strands to the PCB, just cut them. The cable lugs have negligible resistance.
Title: Re: kWeld - "Next level" DIY battery spot welder
Post by: LuboN on January 06, 2018, 09:08:18 AM
Try to use two or three smaller capacity LiPos parallel, that way the resistance of leads and connectors divide  ;)
Title: Re: kWeld - "Next level" DIY battery spot welder
Post by: Kjelt on January 06, 2018, 09:24:18 AM
I plan to sell the capacitor balancer board with and without capacitors.
Please sent me a pm if these are for sale in your shop  :-+
Title: Re: kWeld - "Next level" DIY battery spot welder
Post by: tatus1969 on January 07, 2018, 10:59:04 PM
I plan to sell the capacitor balancer board with and without capacitors.
Please sent me a pm if these are for sale in your shop  :-+
Can I ask you to subscribe to the website newsletter? It's because I'm likely to forget doing that when it's time. I know myself better ;-)
Title: Re: kWeld - "Next level" DIY battery spot welder
Post by: Kjelt on January 07, 2018, 11:57:05 PM
I plan to sell the capacitor balancer board with and without capacitors.
Please sent me a pm if these are for sale in your shop  :-+
Can I ask you to subscribe to the website newsletter? It's because I'm likely to forget doing that when it's time. I know myself better ;-)
Done, i think..........
I press the subscribe button but nothing further happens?
Title: Re: kWeld - "Next level" DIY battery spot welder
Post by: tatus1969 on January 09, 2018, 12:33:46 AM
I have received pictures of this beautiful case from a customer. It is laser cut material from 3mm panels, which should also be more cost effective than 3D printed parts.

(https://endless-sphere.com/forums/download/file.php?id=226856)

I've made his design available here for you to download: https://www.kicksurfer.de/index.php/product/kweld-lasercut-housing/ (https://www.kicksurfer.de/index.php/product/kweld-lasercut-housing/)
Title: Re: kWeld - "Next level" DIY battery spot welder
Post by: arcol on January 09, 2018, 09:24:25 PM
Bear with me, if it is slightly offtopic question.

I would like to build some battery pack for power tools (different brand, so I want to unify them).
I'm looking for these type of connectors not really important which type I end up with,
only want to have pairs. Please see the attached picture.
 
So I can build adapters. I don't know the proper english term, or I'm really unlucky, but can not find
anywhere (ebay, mouser, lcsc.com).

Can somebody tell me how could I source such connectors?
These is the only obstacle between me and a spot welder... :)
Title: Re: kWeld - "Next level" DIY battery spot welder
Post by: anishkgt on January 09, 2018, 09:32:23 PM
Those seem like some lithium battery pack connectors. I suggest you start another thread for this. You would get more response add more pics mention where this is taken from like what device and what it originally connects to.
Title: Re: kWeld - "Next level" DIY battery spot welder
Post by: tatus1969 on January 10, 2018, 09:30:53 AM
new stock is coming, and I've just opened for pre-orders at the shop! --> https://www.keenlab.de/index.php/product-category/kspot-welder-kit/ (https://www.keenlab.de/index.php/product-category/kspot-welder-kit/)
Title: Re: kWeld - &quot;Next level&quot; DIY battery spot welder
Post by: anishkgt on January 12, 2018, 06:32:03 AM
Hey frank since your high power designs for this project, thought I’d share this article that I came across

 https://www.allaboutcircuits.com/news/how-mosfet-arrays-balance-supercapacitor-cells/?utm_source=All+About+Circuits+Members&utm_campaign=80d6eb1df1-EMAIL_CAMPAIGN_2017_12_22&utm_medium=email&utm_term=0_2565529c4b-80d6eb1df1-272670005/ (https://www.allaboutcircuits.com/news/how-mosfet-arrays-balance-supercapacitor-cells/?utm_source=All+About+Circuits+Members&utm_campaign=80d6eb1df1-EMAIL_CAMPAIGN_2017_12_22&utm_medium=email&utm_term=0_2565529c4b-80d6eb1df1-272670005/)


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Title: Re: kWeld - &quot;Next level&quot; DIY battery spot welder
Post by: tatus1969 on January 12, 2018, 10:35:06 PM
Hey frank since your high power designs for this project, thought I’d share this article that I came across

 [url=https://www.allaboutcircuits.com/news/how-mosfet-arrays-balance-supercapacitor-cells/?utm_source=All+About+Circuits+Members&utm_campaign=80d6eb1df1-EMAIL_CAMPAIGN_2017_12_22&utm_medium=email&utm_term=0_2565529c4b-80d6eb1df1-272670005/]https://www.allaboutcircuits.com/news/how-mosfet-arrays-balance-supercapacitor-cells/?utm_source=All+About+Circuits+Members&utm_campaign=80d6eb1df1-EMAIL_CAMPAIGN_2017_12_22&utm_medium=email&utm_term=0_2565529c4b-80d6eb1df1-272670005/ (https://www.allaboutcircuits.com/news/how-mosfet-arrays-balance-supercapacitor-cells/?utm_source=All+About+Circuits+Members&utm_campaign=80d6eb1df1-EMAIL_CAMPAIGN_2017_12_22&utm_medium=email&utm_term=0_2565529c4b-80d6eb1df1-272670005/)[/URL]


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Equipments: DSO104z, Hakko FX888D, Brymen BM869s
That is an interesting idea, they juse use matched MOSFETs with precise gate threshold voltages. The circuit complexity cannot get lower than that.

As I will use the capacitors under extreme conditions, I expect them to start drifting quicker than if they were used for some kind of backup. This is why my balancer is a bit more complex and uses some comparators. It is a kind of intelligent balancing technique that decides which cells to discharge based on the average voltage from the pack. This way it is only reducing voltage of those cells that are a certain delta above the others. The circuit is still cheap because it doesn`t use anything else than jellybean comparators, some MOSFETs and shunt resistors.
Title: Re: kWeld - &quot;Next level&quot; DIY battery spot welder
Post by: anishkgt on January 12, 2018, 10:47:22 PM
Good to know.


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