Author Topic: kWeld - "Next level" DIY battery spot welder  (Read 98658 times)

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Offline Fraser

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Re: kWeld - "Next level" DIY battery spot welder
« Reply #450 on: November 04, 2017, 06:15:11 am »
Thanks Frank,

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

Best Wishes

Fraser
 

Offline tatus1969

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Re: kWeld - "Next level" DIY battery spot welder
« Reply #451 on: November 04, 2017, 10:34:35 am »
Will you make the new firmware available as well at some point in time please ?
Yes of course :-) Otherwise the firmware update dongle would not make much sense ;-) I plan a kWeld product page that will contain links to available firmware versions together with the revision history.
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Offline tatus1969

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Re: kWeld - "Next level" DIY battery spot welder
« Reply #452 on: November 04, 2017, 11:41:46 pm »
This is one funny looking j-link.  Did Segger change the design recently?
Leo
That is an older version I got long ago from ebay. Hopefully not a clone?
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Offline Fraser

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Re: kWeld - "Next level" DIY battery spot welder
« Reply #453 on: November 05, 2017, 12:41:28 am »
Frank,

I have received the V2 to V3 upgrade information pack.

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

Best Wishes

Fraser
 

Offline tatus1969

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Re: kWeld - "Next level" DIY battery spot welder
« Reply #454 on: November 05, 2017, 01:00:32 am »
I have received the V2 to V3 upgrade information pack.

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

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

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

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

UPDATE: the parts are 7.78€ per set, so I would need at least 7 requests to get above Digikey's free shipping threshold. I will ship in simple envelopes for 0.90€.
« Last Edit: November 05, 2017, 02:09:17 am by tatus1969 »
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Offline Fraser

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Re: kWeld - "Next level" DIY battery spot welder
« Reply #455 on: November 05, 2017, 01:32:04 am »
Frank,

What a very kind offer.

I personally will happily pay for the parts.

PM on its way :)

Best Wishes

Fraser
 

Offline Leo Bodnar

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Re: kWeld - "Next level" DIY battery spot welder
« Reply #456 on: November 05, 2017, 03:28:13 am »
This is one funny looking j-link.  Did Segger change the design recently?
Leo
That is an older version I got long ago from ebay. Hopefully not a clone?
Looks totally legit.
« Last Edit: November 05, 2017, 03:30:08 am by Leo Bodnar »
 

Offline eKretz

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Re: kWeld - "Next level" DIY battery spot welder
« Reply #457 on: November 19, 2017, 10:26:17 am »
Pre-orders are already all sold out, eh?
 

Offline tatus1969

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Re: kWeld - "Next level" DIY battery spot welder
« Reply #458 on: November 19, 2017, 10:11:15 pm »
Pre-orders are already all sold out, eh?
I apparently underestimated the demand, and ran out of stock by just pre-orders in less than a week. I plan another batch right after having received the current one. I'll inform again through the newsletter. But in order help me estimate the demand, I have just implemented an "inform me on availability" button for the sold out products that puts you on a waiting list when you click it.
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Offline Derriell

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Re: kWeld - "Next level" DIY battery spot welder
« Reply #459 on: November 25, 2017, 08:26:22 am »
What is the recommended internal resistance of a 2S LiPo battery pack for max 1500A?

Is my following calculation correct?

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

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

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

Thank you
 

Offline tatus1969

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Re: kWeld - "Next level" DIY battery spot welder
« Reply #460 on: November 25, 2017, 08:39:35 pm »
What is the recommended internal resistance of a 2S LiPo battery pack for max 1500A?

Is my following calculation correct?

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

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

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

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

You don't need to worry about undervolting the battery when using it like this, that voltage is related to the chemistry and not to the output voltage under load. You should respect the output current capacity of the pack though, as standard 50C packs get damaged from the high current. So far only the ultra high current packs like Turnigy nanotech or graphite have been tested to be considerably robust. But respect the three golden Lipo rules anyway: a) only operate them with great caution, b) store them in a fire safe place when not using them, and c) charge them under supervision only.
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Offline Derriell

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Re: kWeld - "Next level" DIY battery spot welder
« Reply #461 on: November 27, 2017, 10:14:03 pm »
Ah yes, thank you! This means, if I want 1500A I need a 2S battery  pack (8V) with:

8V/1500A - 3.4mOhm = ~ 2mOhm
 

Offline tatus1969

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Re: kWeld - "Next level" DIY battery spot welder
« Reply #462 on: November 28, 2017, 09:01:47 pm »
Ah yes, thank you! This means, if I want 1500A I need a 2S battery  pack (8V) with:

8V/1500A - 3.4mOhm = ~ 2mOhm
exactly!
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Offline Derriell

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Re: kWeld - "Next level" DIY battery spot welder
« Reply #463 on: December 04, 2017, 12:12:42 am »
A 2S6P pack with the new Samsung SDI INR21700-30T cells with just 10mOhm is good for around 1000A welding power. I find them even more interesting to make nice and power full battery packs  :-+ If you get them for 5$ per cell that makes it 60$.

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

I'm not sure about the power source yet though. I might as well just use several 3S RC-LiPos with 4mm gold connector in parallel for the welding. When I weld I can't fly anyway  ;) 4-6 3S packs should do the jobs just fine with an adapter cable. But a problem with this seems to be that every time I want to weld I need to charge the batteries to the same voltage and if I want to store them later I need to discharge them a bit.
 

Offline tatus1969

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Re: kWeld - "Next level" DIY battery spot welder
« Reply #464 on: December 04, 2017, 10:04:18 pm »
A 2S6P pack with the new Samsung SDI INR21700-30T cells with just 10mOhm is good for around 1000A welding power. I find them even more interesting to make nice and power full battery packs  :-+ If you get them for 5$ per cell that makes it 60$.

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

I'm not sure about the power source yet though. I might as well just use several 3S RC-LiPos with 4mm gold connector in parallel for the welding. When I weld I can't fly anyway  ;) 4-6 3S packs should do the jobs just fine with an adapter cable. But a problem with this seems to be that every time I want to weld I need to charge the batteries to the same voltage and if I want to store them later I need to discharge them a bit.
In the calculations, remember to take the total resistance of the welder into account as well. For kWeld, that is around 2.5mOhms. And the weld spot itself accounts for another 0-2mOhms.
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Offline tatus1969

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Re: kWeld - "Next level" DIY battery spot welder
« Reply #465 on: December 04, 2017, 10:32:24 pm »
I'm happy to announce the release of kWeld firmware rev2.0. It is backwards compatible with the existing rev2 modules as well the new rev3 ones that are on the way to me.

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

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

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

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

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

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

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Re: kWeld - "Next level" DIY battery spot welder
« Reply #466 on: December 05, 2017, 04:48:17 am »
Excellent work Frank  :-+

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

A very big 'Thank You'

Fraser
 

Offline tatus1969

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Re: kWeld - "Next level" DIY battery spot welder
« Reply #467 on: December 05, 2017, 07:51:49 am »
Excellent work Frank  :-+

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

A very big 'Thank You'

Fraser
you're welcome :-) Did you receive your upgrade kit already?
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Offline Fraser

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Re: kWeld - "Next level" DIY battery spot welder
« Reply #468 on: December 05, 2017, 08:06:38 am »
Hi Frank,

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

Fraser
 

Offline TopQuark

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Re: kWeld - "Next level" DIY battery spot welder
« Reply #469 on: December 06, 2017, 04:27:01 am »
Hi Frank, newbie here :D I have looked at the schematics you've posted and are very curious about how you measure current through the welder. I see your circuit measuring voltage at the input, out+ and out-. The input fuse and the parallel mosfets does have resistance and allows current to be derived, but are those resistance alone precise and stable enough to be used as a shunt? Or do you measure current with other clever methods? Hope this is not too much of a commercial secret for you to share.  :P

Alex
 

Offline anishkgt

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Re: kWeld - "Next level" DIY battery spot welder
« Reply #470 on: December 06, 2017, 07:04:03 am »
He has answered it earlier for the same question I had asked. Scroll to page from 1-6 or something if I can recall.


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Offline TopQuark

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Re: kWeld - "Next level" DIY battery spot welder
« Reply #471 on: December 06, 2017, 03:39:48 pm »
Not sure I got it correctly or not. So the kWeld determines current draw by measuring voltage drop across the welding cables and electrodes? Does the welder rely on the length and thickness of welding cables used to be the same as those provided by Frank? I apologize if I am asking too much.

To be really honest, I am trying to replicate one for myself to learn electronics. Being a undergraduate freshman who don't have a major yet, I definitely dare not sell my potential product to others, I might even blow up my dorm room in the process of trying to build one :-DD Also I am too broke to buy the real deal from Frank.
 

Offline tatus1969

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Re: kWeld - "Next level" DIY battery spot welder
« Reply #472 on: December 06, 2017, 08:52:39 pm »
Not sure I got it correctly or not. So the kWeld determines current draw by measuring voltage drop across the welding cables and electrodes? Does the welder rely on the length and thickness of welding cables used to be the same as those provided by Frank? I apologize if I am asking too much.

To be really honest, I am trying to replicate one for myself to learn electronics. Being a undergraduate freshman who don't have a major yet, I definitely dare not sell my potential product to others, I might even blow up my dorm room in the process of trying to build one :-DD Also I am too broke to buy the real deal from Frank.
kWeld is measuring current through the on-state resistance of the MOSFETs, using them as a shunt. This is not very accurate as you suspected, you end up with something in the order of +-30%. And there is quite a temperature coefficient. But absolute accuracy is not that important here, the idea is to have repeatable results. The user will adjust the pulse energy to his needs anyway. The temperature coefficient is more important, and that is one of the reasons why I have chosen the most powerful MOSFETs available (at quite a cost), because they do not heat up much. Even during my torture tests, I never managed to heat them above 50°C.
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Offline anishkgt

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kWeld - "Next level" DIY battery spot welder
« Reply #473 on: December 06, 2017, 08:59:04 pm »
Well if you want accurate current measurement, one way would be to measure the resistance of the cable via 4 wire method and measure voltage on portion of the cable like 10cm apart then use ohms law to calculate current.

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


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Offline Fraser

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Re: kWeld - "Next level" DIY battery spot welder
« Reply #474 on: December 06, 2017, 09:13:16 pm »
On the matter of current measurement accuracy, I concur with Frank.

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

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

Fraser
« Last Edit: December 07, 2017, 02:17:19 am by Fraser »
 


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