Author Topic: kWeld - "Next level" DIY battery spot welder  (Read 47858 times)

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Offline tatus1969

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kWeld - "Next level" DIY battery spot welder
« 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? ;)

« Last Edit: July 18, 2017, 01:57:12 AM by tatus1969 »
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Offline Paul Price

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Re: Guesses on what I am attempting here?
« Reply #1 on: June 14, 2017, 07:38:57 AM »
A waste of time.
 
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Offline Paul Price

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Re: Guesses on what I am attempting here?
« Reply #2 on: June 14, 2017, 07:41:52 AM »
2nd Guess: Remote voltage sensing also incorporating a fused power connection.
 

Offline CM800

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Re: Guesses on what I am attempting here?
« Reply #3 on: June 14, 2017, 07:49:37 AM »
Depends... what is that black brick?

if it's a FET... coilgun! :D
 

Offline Electro Detective

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Re: Guesses on what I am attempting here?
« Reply #4 on: June 14, 2017, 08:54:36 AM »
Some sort of payback device for a Neighbors From Hell electrical switchboard ?  >:D

 :popcorn:
 

Offline MK14

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Re: Guesses on what I am attempting here?
« Reply #5 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 ?
 
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Offline buck converter

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Re: Guesses on what I am attempting here?
« Reply #6 on: June 14, 2017, 09:23:34 AM »
welder?
Just me and my scope.
 

Offline Koen

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Re: Guesses on what I am attempting here?
« Reply #7 on: June 14, 2017, 09:29:19 AM »
A very-rugged armband for your smartphone ?
 

Offline MK14

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Re: Guesses on what I am attempting here?
« Reply #8 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.
 

Online blueskull

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Re: Guesses on what I am attempting here?
« Reply #9 on: June 14, 2017, 09:52:39 AM »
Spot welder.
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Offline mjkuwp

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Re: Guesses on what I am attempting here?
« Reply #10 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 : (
 

Offline StillTrying

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Re: Guesses on what I am attempting here?
« Reply #11 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!

Online BrianHG

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Re: Guesses on what I am attempting here?
« Reply #12 on: June 14, 2017, 10:47:09 AM »
A solar battery charger/inverter switch.
__________
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Offline P90

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Re: Guesses on what I am attempting here?
« Reply #13 on: June 14, 2017, 10:58:12 AM »
2 hours?
You're fired!   :-DD
 
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Offline Electro Detective

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Re: Guesses on what I am attempting here?
« Reply #14 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

 

Offline P90

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Re: Guesses on what I am attempting here?
« Reply #15 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:
 

Offline macona

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Re: Guesses on what I am attempting here?
« Reply #16 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?
 

Offline tatus1969

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Re: Guesses on what I am attempting here?
« Reply #17 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
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Offline tatus1969

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Re: Guesses on what I am attempting here?
« Reply #18 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)
« Last Edit: June 14, 2017, 05:22:07 PM by tatus1969 »
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Offline tatus1969

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Re: Guesses on what I am attempting here?
« Reply #19 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...
« Last Edit: June 17, 2017, 09:00:52 PM by tatus1969 »
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Offline tatus1969

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Re: Guesses on what I am attempting here?
« Reply #20 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 :)
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Online tautech

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Re: Guesses on what I am attempting here?
« Reply #21 on: June 14, 2017, 03:54:41 PM »
Run isolator for charging your electric scooter conversion.
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Offline tatus1969

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Re: Guesses on what I am attempting here?
« Reply #22 on: June 14, 2017, 04:51:17 PM »
spoiler alert: the correct anwer was already given :clap:
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Offline CM800

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Re: Guesses on what I am attempting here?
« Reply #23 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
 

Offline tatus1969

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Offline tatus1969

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Re: Guesses on what I am attempting here?
« Reply #26 on: June 14, 2017, 09:34:01 PM »
I find it funny though that there is such a huge difference between SOT227 and SOT223 ^-^
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Offline P90

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Re: Guesses on what I am attempting here?
« Reply #27 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...
 

Offline tatus1969

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Re: Guesses on what I am attempting here?
« Reply #28 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.
« Last Edit: June 14, 2017, 09:54:31 PM by tatus1969 »
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Offline tatus1969

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Re: Guesses on what I am attempting here?
« Reply #29 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:



DETAIL A

« Last Edit: June 15, 2017, 07:24:36 AM by tatus1969 »
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Online blueskull

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Re: Guesses on what I am attempting here?
« Reply #30 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.
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Offline DBecker

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Re: Guesses on what I am attempting here?
« Reply #31 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.
 

Online blueskull

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Re: Guesses on what I am attempting here?
« Reply #32 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.
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Offline macona

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Re: Guesses on what I am attempting here?
« Reply #33 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.
 

Online blueskull

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Re: Guesses on what I am attempting here?
« Reply #34 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).
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Offline LukeW

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Re: Guesses on what I am attempting here?
« Reply #35 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.
 

Offline buck converter

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Re: Guesses on what I am attempting here?
« Reply #36 on: June 15, 2017, 11:20:01 AM »
high voltage Molotov cocktail. if that makes any sense
Just me and my scope.
 

Offline LukeW

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Re: Guesses on what I am attempting here?
« Reply #37 on: June 15, 2017, 01:54:25 PM »
So those beer bottles are supposed to be HV insulated standoffs?
 

Offline tatus1969

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Re: Guesses on what I am attempting here?
« Reply #38 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.
« Last Edit: June 15, 2017, 04:45:55 PM by tatus1969 »
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Offline tatus1969

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Re: Guesses on what I am attempting here?
« Reply #39 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.





« Last Edit: June 17, 2017, 10:16:35 AM by tatus1969 »
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Offline Bendba

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Re: Guesses on what I am attempting here?
« Reply #40 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?
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Online blueskull

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Re: Guesses on what I am attempting here?
« Reply #41 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.
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Offline tatus1969

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Re: Guesses on what I am attempting here?
« Reply #42 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.
« Last Edit: June 17, 2017, 06:12:52 PM by tatus1969 »
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Offline tatus1969

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Re: low cost DIY battery spot welder [guesses on ... - solved]
« Reply #43 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?
« Last Edit: June 19, 2017, 03:34:01 AM by tatus1969 »
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Offline tatus1969

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Re: low cost DIY battery spot welder [guesses on ... - solved]
« Reply #44 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.
« Last Edit: June 19, 2017, 06:20:23 AM by tatus1969 »
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Offline tatus1969

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Re: low cost DIY battery spot welder [guesses on ... - solved]
« Reply #45 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:



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
« Last Edit: June 24, 2017, 10:33:01 PM by tatus1969 »
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Offline tatus1969

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Re: low cost DIY battery spot welder [guesses on ... - solved]
« Reply #46 on: June 24, 2017, 06:14:12 AM »
The design is finished, boards and parts are ordered  :phew:
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Offline bktemp

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Re: low cost DIY battery spot welder [guesses on ... - solved]
« Reply #47 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.
 
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Offline tatus1969

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Re: low cost DIY battery spot welder [guesses on ... - solved]
« Reply #48 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:
« Last Edit: June 24, 2017, 06:56:33 AM by tatus1969 »
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Offline MagicSmoker

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Re: low cost DIY battery spot welder [guesses on ... - solved]
« Reply #49 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.

 

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Re: low cost DIY battery spot welder [guesses on ... - solved]
« Reply #50 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.
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Offline tatus1969

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Re: low cost DIY battery spot welder [guesses on ... - solved]
« Reply #51 on: June 25, 2017, 12:53:38 AM »
Assembled module...



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Offline tatus1969

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Re: low cost DIY battery spot welder [guesses on ... - solved]
« Reply #52 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)?

« Last Edit: July 02, 2017, 08:52:00 PM by tatus1969 »
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Re: low cost DIY battery spot welder [guesses on ... - solved]
« Reply #53 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.
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Online mk_

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Re: low cost DIY battery spot welder [guesses on ... - solved]
« Reply #54 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
 

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Re: low cost DIY battery spot welder [guesses on ... - solved]
« Reply #55 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. ::)
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Offline tatus1969

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Re: low cost DIY battery spot welder [guesses on ... - solved]
« Reply #56 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.



« Last Edit: July 06, 2017, 07:31:08 PM by tatus1969 »
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Offline tatus1969

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Re: low cost DIY battery spot welder [guesses on ... - solved]
« Reply #57 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:



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
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Offline tatus1969

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Re: low cost DIY battery spot welder [guesses on ... - solved]
« Reply #58 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!


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Offline Fraser

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Re: low cost DIY battery spot welder [guesses on ... - solved]
« Reply #59 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
« Last Edit: July 09, 2017, 09:30:45 PM by Fraser »
 

Offline tatus1969

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Re: low cost DIY battery spot welder [guesses on ... - solved]
« Reply #60 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.
« Last Edit: July 10, 2017, 01:52:40 AM by tatus1969 »
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Offline Fraser

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Re: low cost DIY battery spot welder [guesses on ... - solved]
« Reply #61 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
 

Offline tatus1969

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Re: low cost DIY battery spot welder [guesses on ... - solved]
« Reply #62 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.


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Offline tatus1969

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Re: low cost DIY battery spot welder [guesses on ... - solved]
« Reply #63 on: July 11, 2017, 05:20:19 PM »
I made a video where I am doing robustnes testing:

« Last Edit: July 11, 2017, 06:54:16 PM by tatus1969 »
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Offline maukka

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Re: low cost DIY battery spot welder [guesses on ... - solved]
« Reply #64 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.
 

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Re: low cost DIY battery spot welder [guesses on ... - solved]
« Reply #65 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.
 

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Re: low cost DIY battery spot welder [guesses on ... - solved]
« Reply #66 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
« Last Edit: July 12, 2017, 03:03:51 AM by Fraser »
 

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Re: low cost DIY battery spot welder [guesses on ... - solved]
« Reply #67 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)
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Re: low cost DIY battery spot welder [guesses on ... - solved]
« Reply #68 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!
« Last Edit: July 12, 2017, 03:03:14 AM by tatus1969 »
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Offline Fraser

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Re: low cost DIY battery spot welder [guesses on ... - solved]
« Reply #69 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
 

Offline SvanGool

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Re: low cost DIY battery spot welder [guesses on ... - solved]
« Reply #70 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.
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Re: low cost DIY battery spot welder [guesses on ... - solved]
« Reply #71 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)
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Offline tatus1969

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Re: low cost DIY battery spot welder [guesses on ... - solved]
« Reply #72 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


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Offline Fraser

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Re: low cost DIY battery spot welder [guesses on ... - solved]
« Reply #73 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

 

Offline casinada

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Re: low cost DIY battery spot welder [guesses on ... - solved]
« Reply #74 on: July 12, 2017, 08:03:31 AM »
 :-+
I'm tempted :)
 

Offline SvanGool

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Re: low cost DIY battery spot welder [guesses on ... - solved]
« Reply #75 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.
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Offline tatus1969

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Re: low cost DIY battery spot welder [guesses on ... - solved]
« Reply #76 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.
:-+
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Offline tatus1969

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Re: low cost DIY battery spot welder [guesses on ... - solved]
« Reply #77 on: July 13, 2017, 06:06:13 AM »
There goes the next video, showing some improvements:

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Offline Kjelt

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Re: low cost DIY battery spot welder [guesses on ... - solved]
« Reply #78 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 ?
 

Offline tatus1969

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Re: low cost DIY battery spot welder [guesses on ... - solved]
« Reply #79 on: July 13, 2017, 08:18:45 AM »
can you make ordering the programmer for future fw updates optional ?
That's the plan!
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Offline Fraser

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Re: low cost DIY battery spot welder [guesses on ... - solved]
« Reply #80 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
« Last Edit: July 13, 2017, 08:53:03 AM by Fraser »
 

Offline Fraser

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Re: low cost DIY battery spot welder [guesses on ... - solved]
« Reply #81 on: July 13, 2017, 08:47:22 AM »
 

Offline Kjelt

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Re: low cost DIY battery spot welder [guesses on ... - solved]
« Reply #82 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  :)
 

Offline tatus1969

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Re: low cost DIY battery spot welder [guesses on ... - solved]
« Reply #83 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...
« Last Edit: July 14, 2017, 01:08:44 AM by tatus1969 »
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Offline tatus1969

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Re: low cost DIY battery spot welder [guesses on ... - solved]
« Reply #84 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:
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Offline SvanGool

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Re: low cost DIY battery spot welder [guesses on ... - solved]
« Reply #85 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.
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Offline Fraser

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Re: low cost DIY battery spot welder [guesses on ... - solved]
« Reply #86 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
 

Offline tatus1969

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Re: low cost DIY battery spot welder [guesses on ... - solved]
« Reply #87 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.
« Last Edit: July 14, 2017, 06:30:38 PM by tatus1969 »
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Offline SvanGool

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Re: low cost DIY battery spot welder [guesses on ... - solved]
« Reply #88 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) 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).
 

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Offline Kjelt

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Re: low cost DIY battery spot welder [guesses on ... - solved]
« Reply #89 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.
 

Offline SvanGool

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Re: low cost DIY battery spot welder [guesses on ... - solved]
« Reply #90 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.
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Offline tatus1969

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Re: low cost DIY battery spot welder [guesses on ... - solved]
« Reply #91 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.
« Last Edit: July 14, 2017, 10:35:29 PM by tatus1969 »
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Offline tatus1969

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Re: low cost DIY battery spot welder [guesses on ... - solved]
« Reply #92 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.
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Offline Fraser

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Re: low cost DIY battery spot welder [guesses on ... - solved]
« Reply #93 on: July 15, 2017, 03:05:10 AM »
Nice new probe design :)

Looking forward to being able to purchase this unit.

Fraser
 

Offline Kjelt

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Re: low cost DIY battery spot welder [guesses on ... - solved]
« Reply #94 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.
 

Offline tatus1969

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Re: low cost DIY battery spot welder [guesses on ... - solved]
« Reply #95 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.
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Offline Fraser

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Re: low cost DIY battery spot welder [guesses on ... - solved]
« Reply #96 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
 

Offline tatus1969

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Re: low cost DIY battery spot welder [guesses on ... - solved]
« Reply #97 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/
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.
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Offline tatus1969

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Re: low cost DIY battery spot welder [guesses on ... - solved]
« Reply #98 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  :-//
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Offline Fraser

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Re: low cost DIY battery spot welder [guesses on ... - solved]
« Reply #99 on: July 15, 2017, 09:21:39 AM »
Reservation request PM sent. I am a committed customer of your kit  :)   :-+

Fraser
 

Offline tatus1969

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Re: low cost DIY battery spot welder [guesses on ... - solved]
« Reply #100 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)
« Last Edit: July 16, 2017, 04:52:39 AM by tatus1969 »
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Offline Fraser

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Re: low cost DIY battery spot welder [guesses on ... - solved]
« Reply #101 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
 

Offline tatus1969

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Re: low cost DIY battery spot welder [guesses on ... - solved]
« Reply #102 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.
« Last Edit: July 16, 2017, 02:57:12 AM by tatus1969 »
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Offline Fraser

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Re: low cost DIY battery spot welder [guesses on ... - solved]
« Reply #103 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
 

Offline tatus1969

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Re: low cost DIY battery spot welder [guesses on ... - solved]
« Reply #104 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.
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Offline Fraser

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Re: low cost DIY battery spot welder [guesses on ... - solved]
« Reply #105 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
 

Offline Kjelt

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Re: low cost DIY battery spot welder [guesses on ... - solved]
« Reply #106 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?
 

Offline tatus1969

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Re: low cost DIY battery spot welder [guesses on ... - solved]
« Reply #107 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.
« Last Edit: July 16, 2017, 08:37:31 AM by tatus1969 »
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Offline Fraser

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Re: low cost DIY battery spot welder [guesses on ... - solved]
« Reply #108 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
 

Offline tatus1969

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Re: low cost DIY battery spot welder [guesses on ... - solved]
« Reply #109 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

Not to forget: the schematic there is not up to date anymore, nor is it working like that 8)
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Offline Fraser

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Re: low cost DIY battery spot welder [guesses on ... - solved]
« Reply #110 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
 

Offline Fraser

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Re: low cost DIY battery spot welder [guesses on ... - solved]
« Reply #111 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
 

Offline TheAmmoniacal

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Re: low cost DIY battery spot welder [guesses on ... - solved]
« Reply #112 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?
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Offline tatus1969

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Re: low cost DIY battery spot welder [guesses on ... - solved]
« Reply #113 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.



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.



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.



« Last Edit: July 16, 2017, 10:47:12 PM by tatus1969 »
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Offline TheAmmoniacal

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Re: low cost DIY battery spot welder [guesses on ... - solved]
« Reply #114 on: July 16, 2017, 10:36:26 PM »
Those welds do look great, no improvement needed! Maybe try a few with flux for fun? :)
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Re: low cost DIY battery spot welder [guesses on ... - solved]
« Reply #115 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.
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Offline tatus1969

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Re: low cost DIY battery spot welder [guesses on ... - solved]
« Reply #116 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  ;)
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Offline Fraser

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Re: low cost DIY battery spot welder [guesses on ... - solved]
« Reply #117 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
 

Offline tatus1969

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Re: low cost DIY battery spot welder [guesses on ... - solved]
« Reply #118 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.
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Offline Fraser

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Re: low cost DIY battery spot welder [guesses on ... - solved]
« Reply #119 on: July 17, 2017, 06:21:10 AM »
Ooooh, I had not thought of that. Interesting.

Fraser
 

Offline Kjelt

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Re: low cost DIY battery spot welder [guesses on ... - solved]
« Reply #120 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 ?

 

Offline tatus1969

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Re: low cost DIY battery spot welder [guesses on ... - solved]
« Reply #121 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
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Offline Fraser

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Re: low cost DIY battery spot welder [guesses on ... - solved]
« Reply #122 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
 

Offline tatus1969

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Re: low cost DIY battery spot welder [guesses on ... - solved]
« Reply #123 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

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.
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Offline Fraser

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Re: low cost DIY battery spot welder [guesses on ... - solved]
« Reply #124 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/

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
 

Offline Fraser

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Re: low cost DIY battery spot welder [guesses on ... - solved]
« Reply #126 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 ?  :-//
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Offline tatus1969

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Re: low cost DIY battery spot welder [guesses on ... - solved]
« Reply #127 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/
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  ;)
« Last Edit: July 17, 2017, 06:27:41 PM by tatus1969 »
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Re: low cost DIY battery spot welder [guesses on ... - solved]
« Reply #128 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 ?
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Offline tatus1969

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Re: low cost DIY battery spot welder [guesses on ... - solved]
« Reply #129 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.
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Offline negativ3

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Re: low cost DIY battery spot welder [guesses on ... - solved]
« Reply #130 on: July 18, 2017, 01:42:22 AM »
Please let us know when Paypal is ready to use.
 

Offline tatus1969

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Re: low cost DIY battery spot welder [guesses on ... - solved]
« Reply #131 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.
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Offline Kjelt

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Re: kWeld - "Next level" DIY battery spot welder
« Reply #132 on: July 18, 2017, 04:31:26 AM »
Oops did we have to wait with the pre-order? I am confused  :-//
 

Offline Fraser

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Re: kWeld - "Next level" DIY battery spot welder
« Reply #133 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
 

Offline Kjelt

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Re: kWeld - "Next level" DIY battery spot welder
« Reply #134 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.
 

Offline tatus1969

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Re: kWeld - "Next level" DIY battery spot welder
« Reply #135 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  ;)
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Offline Kjelt

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Re: kWeld - "Next level" DIY battery spot welder
« Reply #136 on: July 18, 2017, 06:50:23 AM »
Good to hear now I don't feel guilty  :)
 

Offline tatus1969

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Re: kWeld - "Next level" DIY battery spot welder
« Reply #137 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!
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Offline tatus1969

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Re: kWeld - "Next level" DIY battery spot welder
« Reply #138 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!
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Offline tatus1969

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Re: kWeld - "Next level" DIY battery spot welder
« Reply #139 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.
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Offline DBecker

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Re: kWeld - "Next level" DIY battery spot welder
« Reply #140 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.

 
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Offline maukka

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Re: kWeld - "Next level" DIY battery spot welder
« Reply #141 on: July 18, 2017, 06:11:03 PM »
I went with a Turnigy Graphene 6000mAh 5S1P 65 battery. According to Mooch they seem to be the best performers in high current applications (low internal resistance).
 

Offline tatus1969

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Re: kWeld - "Next level" DIY battery spot welder
« Reply #142 on: July 18, 2017, 06:45:41 PM »
I went with a Turnigy Graphene 6000mAh 5S1P 65 battery. According to Mooch 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.
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Offline BFX

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Re: kWeld - "Next level" DIY battery spot welder
« Reply #143 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:
 

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Re: kWeld - "Next level" DIY battery spot welder
« Reply #144 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.
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Offline tatus1969

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Re: kWeld - "Next level" DIY battery spot welder
« Reply #145 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  :-+





« Last Edit: July 21, 2017, 12:34:18 AM by tatus1969 »
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Offline Kjelt

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Re: kWeld - "Next level" DIY battery spot welder
« Reply #146 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.
 

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Re: kWeld - "Next level" DIY battery spot welder
« Reply #147 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
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Offline tatus1969

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Re: kWeld - "Next level" DIY battery spot welder
« Reply #148 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.





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Offline Fraser

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Re: kWeld - "Next level" DIY battery spot welder
« Reply #149 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

Fraser
« Last Edit: July 21, 2017, 09:11:07 AM by Fraser »
 

Offline cs.dk

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Re: kWeld - "Next level" DIY battery spot welder
« Reply #150 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
 

Offline Fraser

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Re: kWeld - "Next level" DIY battery spot welder
« Reply #151 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
 

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Re: kWeld - "Next level" DIY battery spot welder
« Reply #152 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.
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Offline cs.dk

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Re: kWeld - "Next level" DIY battery spot welder
« Reply #153 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.
 

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Re: kWeld - "Next level" DIY battery spot welder
« Reply #154 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.
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Offline cs.dk

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Re: kWeld - "Next level" DIY battery spot welder
« Reply #155 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.
 

Offline Fraser

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Re: kWeld - "Next level" DIY battery spot welder
« Reply #156 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
 

Offline tatus1969

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Re: kWeld - "Next level" DIY battery spot welder
« Reply #157 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

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.
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Offline Kjelt

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Re: kWeld - "Next level" DIY battery spot welder
« Reply #158 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.
 

Offline cs.dk

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Re: kWeld - "Next level" DIY battery spot welder
« Reply #159 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 ;)
 

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Re: kWeld - "Next level" DIY battery spot welder
« Reply #160 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 :-//
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Offline Fraser

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Re: kWeld - "Next level" DIY battery spot welder
« Reply #161 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
« Last Edit: July 25, 2017, 08:37:45 AM by Fraser »
 

Offline tatus1969

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Re: kWeld - "Next level" DIY battery spot welder
« Reply #162 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
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Offline tatus1969

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Re: kWeld - "Next level" DIY battery spot welder
« Reply #163 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

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Offline Fraser

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Re: kWeld - "Next level" DIY battery spot welder
« Reply #164 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
 

Offline tatus1969

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Re: kWeld - "Next level" DIY battery spot welder
« Reply #165 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:
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Offline tatus1969

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Re: kWeld - "Next level" DIY battery spot welder
« Reply #166 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/  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.


« Last Edit: July 31, 2017, 10:12:36 AM by tatus1969 »
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Offline Fraser

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Re: kWeld - "Next level" DIY battery spot welder
« Reply #167 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
 

Offline Kjelt

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Re: kWeld - "Next level" DIY battery spot welder
« Reply #168 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/  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?
 

Offline Fraser

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Re: kWeld - "Next level" DIY battery spot welder
« Reply #169 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
 

Offline Kjelt

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Re: kWeld - "Next level" DIY battery spot welder
« Reply #170 on: July 31, 2017, 09:42:35 PM »
Yes thanks, the email had some delay but it is all clear now  :-+
 

Offline tatus1969

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Re: kWeld - "Next level" DIY battery spot welder
« Reply #171 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
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Offline tatus1969

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Re: kWeld - "Next level" DIY battery spot welder
« Reply #172 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).


« Last Edit: August 01, 2017, 01:26:11 AM by tatus1969 »
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Offline Kjelt

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Re: kWeld - "Next level" DIY battery spot welder
« Reply #173 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  ;)
 

Offline tatus1969

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Re: kWeld - "Next level" DIY battery spot welder
« Reply #174 on: August 01, 2017, 01:56:13 AM »
almost time for a CNC  ;)
definitely!!
Your living is determined not so much by what life brings to you as by the attitude you bring to life; not so much by what happens to you as by the way your mind looks at what happens.

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Offline Fraser

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Re: kWeld - "Next level" DIY battery spot welder
« Reply #175 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
« Last Edit: August 01, 2017, 05:33:33 AM by Fraser »
 

Offline kony

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Re: kWeld - "Next level" DIY battery spot welder
« Reply #176 on: August 01, 2017, 03:47:36 AM »
Get the aluminium busbars nickel plated. Cheap & effective corrosion protection.
 

Offline tatus1969

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Re: kWeld - "Next level" DIY battery spot welder
« Reply #177 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.
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Offline tatus1969

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Re: kWeld - "Next level" DIY battery spot welder
« Reply #178 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.
Your living is determined not so much by what life brings to you as by the attitude you bring to life; not so much by what happens to you as by the way your mind looks at what happens.

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Offline tatus1969

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Re: kWeld - "Next level" DIY battery spot welder
« Reply #179 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.




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Offline Fraser

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Re: kWeld - "Next level" DIY battery spot welder
« Reply #180 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
« Last Edit: August 02, 2017, 09:06:09 AM by Fraser »
 

Offline fuzzoli

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Re: kWeld - "Next level" DIY battery spot welder
« Reply #181 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!
 

Offline tatus1969

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Re: kWeld - "Next level" DIY battery spot welder
« Reply #182 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.
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Offline Fraser

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Re: kWeld - "Next level" DIY battery spot welder
« Reply #183 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
 

Offline tatus1969

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Re: kWeld - "Next level" DIY battery spot welder
« Reply #184 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.
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Offline tatus1969

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Re: kWeld - "Next level" DIY battery spot welder
« Reply #185 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.
« Last Edit: August 05, 2017, 06:43:08 AM by tatus1969 »
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Offline Fraser

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Re: kWeld - "Next level" DIY battery spot welder
« Reply #186 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
« Last Edit: August 05, 2017, 04:16:09 AM by Fraser »
 

Offline tatus1969

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Re: kWeld - "Next level" DIY battery spot welder
« Reply #187 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)
« Last Edit: August 05, 2017, 06:30:34 AM by tatus1969 »
Your living is determined not so much by what life brings to you as by the attitude you bring to life; not so much by what happens to you as by the way your mind looks at what happens.

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Offline Kjelt

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Re: kWeld - "Next level" DIY battery spot welder
« Reply #188 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  :-+  :-+  :-+
 

Offline tatus1969

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Re: kWeld - "Next level" DIY battery spot welder
« Reply #189 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  ;)
Your living is determined not so much by what life brings to you as by the attitude you bring to life; not so much by what happens to you as by the way your mind looks at what happens.

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Offline tatus1969

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Re: kWeld - "Next level" DIY battery spot welder
« Reply #190 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.
Your living is determined not so much by what life brings to you as by the attitude you bring to life; not so much by what happens to you as by the way your mind looks at what happens.

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Offline Kjelt

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Re: kWeld - "Next level" DIY battery spot welder
« Reply #191 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?
 

Offline tatus1969

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Re: kWeld - "Next level" DIY battery spot welder
« Reply #192 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.
Your living is determined not so much by what life brings to you as by the attitude you bring to life; not so much by what happens to you as by the way your mind looks at what happens.

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Offline Kjelt

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Re: kWeld - "Next level" DIY battery spot welder
« Reply #193 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.
 

Offline tatus1969

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Re: kWeld - "Next level" DIY battery spot welder
« Reply #194 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.
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Offline tatus1969

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Re: kWeld - "Next level" DIY battery spot welder
« Reply #195 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:



- 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/


- 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.


- 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). 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

- 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.


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.
Your living is determined not so much by what life brings to you as by the attitude you bring to life; not so much by what happens to you as by the way your mind looks at what happens.

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Offline Kjelt

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Re: kWeld - "Next level" DIY battery spot welder
« Reply #196 on: August 14, 2017, 03:02:18 AM »
 :-+ very nice improvements again.
 

Offline mzzj

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Re: kWeld - "Next level" DIY battery spot welder
« Reply #197 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.
 

Online Marco

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Re: kWeld - "Next level" DIY battery spot welder
« Reply #198 on: August 15, 2017, 07:16:42 PM »
Why would 60v not work? Too much energy in too little time?
 

Offline Kjelt

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Re: kWeld - "Next level" DIY battery spot welder
« Reply #199 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.
 

Offline Fraser

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Re: kWeld - "Next level" DIY battery spot welder
« Reply #200 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
 

Offline mzzj

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Re: kWeld - "Next level" DIY battery spot welder
« Reply #201 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)
 

Offline tatus1969

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Re: kWeld - "Next level" DIY battery spot welder
« Reply #202 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.
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Offline tatus1969

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Re: kWeld - "Next level" DIY battery spot welder
« Reply #203 on: August 16, 2017, 01:42:41 AM »
I've got some work on my desk   :D

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Online Marco

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Re: kWeld - "Next level" DIY battery spot welder
« Reply #204 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.
 

Offline tatus1969

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Re: kWeld - "Next level" DIY battery spot welder
« Reply #205 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.
« Last Edit: August 18, 2017, 08:37:49 AM by tatus1969 »
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Offline Fraser

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Re: kWeld - "Next level" DIY battery spot welder
« Reply #206 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
« Last Edit: August 19, 2017, 01:45:50 AM by Fraser »
 

Offline tatus1969

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Re: kWeld - "Next level" DIY battery spot welder
« Reply #207 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.
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Offline SirJMD

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Re: kWeld - "Next level" DIY battery spot welder
« Reply #208 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.
 

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Re: kWeld - "Next level" DIY battery spot welder
« Reply #209 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.
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Offline SirJMD

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Re: kWeld - "Next level" DIY battery spot welder
« Reply #210 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.
 

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Re: kWeld - "Next level" DIY battery spot welder
« Reply #211 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.
« Last Edit: August 25, 2017, 08:07:01 AM by tatus1969 »
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Offline tatus1969

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Re: kWeld - "Next level" DIY battery spot welder
« Reply #212 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.
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Offline Kjelt

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Re: kWeld - "Next level" DIY battery spot welder
« Reply #213 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.
 

Offline Fraser

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Re: kWeld - "Next level" DIY battery spot welder
« Reply #214 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
 

Offline tatus1969

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Re: kWeld - "Next level" DIY battery spot welder
« Reply #215 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€.
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Offline Kjelt

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Re: kWeld - "Next level" DIY battery spot welder
« Reply #216 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 ?
 

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Re: kWeld - "Next level" DIY battery spot welder
« Reply #217 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
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Online Marco

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Re: kWeld - "Next level" DIY battery spot welder
« Reply #218 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.
« Last Edit: August 26, 2017, 08:48:51 AM by Marco »
 

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Re: kWeld - "Next level" DIY battery spot welder
« Reply #219 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.
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Online Marco

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Re: kWeld - "Next level" DIY battery spot welder
« Reply #220 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 :/
 

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Re: kWeld - "Next level" DIY battery spot welder
« Reply #221 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.
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Offline SirJMD

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Re: kWeld - "Next level" DIY battery spot welder
« Reply #222 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.
 

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Re: kWeld - "Next level" DIY battery spot welder
« Reply #223 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
« Last Edit: August 27, 2017, 08:32:01 AM by tatus1969 »
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Offline Kjelt

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Re: kWeld - "Next level" DIY battery spot welder
« Reply #224 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?
« Last Edit: August 27, 2017, 07:25:01 PM by Kjelt »
 

Offline JohnG

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Re: kWeld - "Next level" DIY battery spot welder
« Reply #225 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
 

Offline anishkgt

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Re: kWeld - "Next level" DIY battery spot welder
« Reply #226 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.
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Re: kWeld - "Next level" DIY battery spot welder
« Reply #227 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  ;)
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Offline Kjelt

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Re: kWeld - "Next level" DIY battery spot welder
« Reply #228 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 , 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  ;)
« Last Edit: August 28, 2017, 07:12:28 AM by Kjelt »
 

Offline ozwolf

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Re: kWeld - "Next level" DIY battery spot welder
« Reply #229 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?

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Offline tatus1969

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Re: kWeld - "Next level" DIY battery spot welder
« Reply #230 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.
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Re: kWeld - "Next level" DIY battery spot welder
« Reply #231 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.
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Offline Kjelt

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Re: kWeld - "Next level" DIY battery spot welder
« Reply #232 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  :)
 

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Re: kWeld - "Next level" DIY battery spot welder
« Reply #233 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.
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Offline Kjelt

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Re: kWeld - "Next level" DIY battery spot welder
« Reply #234 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  :-+
 

Offline tatus1969

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Re: kWeld - "Next level" DIY battery spot welder
« Reply #235 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). 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...  ???
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Offline SvanGool

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Re: kWeld - "Next level" DIY battery spot welder
« Reply #236 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.
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Offline Kjelt

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Re: kWeld - "Next level" DIY battery spot welder
« Reply #237 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)
 

Offline anishkgt

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Re: kWeld - &quot;Next level&quot; DIY battery spot welder
« Reply #238 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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Offline tatus1969

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Re: kWeld - "Next level" DIY battery spot welder
« Reply #239 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.
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Offline tatus1969

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Re: kWeld - &quot;Next level&quot; DIY battery spot welder
« Reply #240 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?
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Offline SvanGool

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Re: kWeld - "Next level" DIY battery spot welder
« Reply #241 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.  :)
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Offline tatus1969

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Re: kWeld - "Next level" DIY battery spot welder
« Reply #242 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  :)
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Offline anishkgt

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Re: kWeld - &quot;Next level&quot; DIY battery spot welder
« Reply #243 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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Offline SirJMD

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Re: kWeld - "Next level" DIY battery spot welder
« Reply #244 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.
 

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Re: kWeld - &quot;Next level&quot; DIY battery spot welder
« Reply #245 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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Offline Kjelt

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Re: kWeld - "Next level" DIY battery spot welder
« Reply #246 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.
« Last Edit: August 29, 2017, 07:47:20 AM by Kjelt »
 

Offline SirJMD

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Re: kWeld - &quot;Next level&quot; DIY battery spot welder
« Reply #247 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.
 

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Re: kWeld - &quot;Next level&quot; DIY battery spot welder
« Reply #248 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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Offline tatus1969

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Re: kWeld - &quot;Next level&quot; DIY battery spot welder
« Reply #249 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.
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Re: kWeld - &quot;Next level&quot; DIY battery spot welder
« Reply #250 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


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Offline tatus1969

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Re: kWeld - "Next level" DIY battery spot welder
« Reply #251 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? :)
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Online tautech

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Re: kWeld - "Next level" DIY battery spot welder
« Reply #252 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.  ;)
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Offline tatus1969

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Re: kWeld - "Next level" DIY battery spot welder
« Reply #253 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  :-+ :-+ :-+
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Re: kWeld - &quot;Next level&quot; DIY battery spot welder
« Reply #254 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.
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Offline anishkgt

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Re: kWeld - &quot;Next level&quot; DIY battery spot welder
« Reply #255 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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Offline tatus1969

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Re: kWeld - &quot;Next level&quot; DIY battery spot welder
« Reply #256 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.
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Offline anishkgt

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Re: kWeld - &quot;Next level&quot; DIY battery spot welder
« Reply #257 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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Re: kWeld - &quot;Next level&quot; DIY battery spot welder
« Reply #258 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.
 

Offline tatus1969

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Re: kWeld - &quot;Next level&quot; DIY battery spot welder
« Reply #259 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.
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Offline anishkgt

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kWeld - "Next level" DIY battery spot welder
« Reply #260 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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Offline Kjelt

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Re: kWeld - &quot;Next level&quot; DIY battery spot welder
« Reply #261 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?
 

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Re: kWeld - &quot;Next level&quot; DIY battery spot welder
« Reply #262 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.
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Offline Kjelt

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Re: kWeld - "Next level" DIY battery spot welder
« Reply #263 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
 

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Re: kWeld - "Next level" DIY battery spot welder
« Reply #264 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
if that is an option for anyone, then I guess I'll have to rethink the price of my welder :-DD
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Re: kWeld - "Next level" DIY battery spot welder
« Reply #265 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:
  • 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:


The graphs:


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, there 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.

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
« Last Edit: August 30, 2017, 09:13:43 PM by SvanGool »
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Offline SirJMD

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Re: kWeld - "Next level" DIY battery spot welder
« Reply #266 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

I think I can top that.. >:D

Might need something to step it down.. 70 Mvar at 132 kV.
 

Offline Kjelt

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Re: kWeld - "Next level" DIY battery spot welder
« Reply #267 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?
 

Offline SirJMD

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Re: kWeld - "Next level" DIY battery spot welder
« Reply #268 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

The graphs:
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.
 

Offline SvanGool

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Re: kWeld - "Next level" DIY battery spot welder
« Reply #269 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.
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Offline tatus1969

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Re: kWeld - "Next level" DIY battery spot welder
« Reply #270 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.
« Last Edit: August 30, 2017, 08:48:52 PM by tatus1969 »
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Offline anishkgt

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kWeld - "Next level" DIY battery spot welder
« Reply #271 on: August 30, 2017, 08:08:50 PM »
A server psu such as https://www.ebay.com/itm/121957144997would help.

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


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Offline SvanGool

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Re: kWeld - "Next level" DIY battery spot welder
« Reply #272 on: August 30, 2017, 09:09:42 PM »
Can you provide the simulation files?
Attached.
I used a standard free LTSpiceIV / LTSpiceXVII 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:




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 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?
« Last Edit: August 30, 2017, 09:42:24 PM by SvanGool »
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Offline anishkgt

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Re: kWeld - &quot;Next level&quot; DIY battery spot welder
« Reply #273 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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Re: kWeld - &quot;Next level&quot; DIY battery spot welder
« Reply #274 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.
 

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Re: kWeld - &quot;Next level&quot; DIY battery spot welder
« Reply #275 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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Re: kWeld - &quot;Next level&quot; DIY battery spot welder
« Reply #276 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.


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18650 cells can have very different chemistries and current ratings. Show me a similar volume LiPo with better current rating than the Sony cell.
 

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Re: kWeld - &quot;Next level&quot; DIY battery spot welder
« Reply #277 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.


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Re: kWeld - &quot;Next level&quot; DIY battery spot welder
« Reply #278 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.
 

Offline SvanGool

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Re: kWeld - &quot;Next level&quot; DIY battery spot welder
« Reply #279 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 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:



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Offline tatus1969

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Re: kWeld - &quot;Next level&quot; DIY battery spot welder
« Reply #280 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 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.
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Offline tatus1969

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Re: kWeld - "Next level" DIY battery spot welder
« Reply #281 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.

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Re: kWeld - &quot;Next level&quot; DIY battery spot welder
« Reply #282 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.


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Offline Kjelt

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Re: kWeld - "Next level" DIY battery spot welder
« Reply #283 on: August 31, 2017, 06:40:22 PM »