Author Topic: kWeld - "Next level" DIY battery spot welder  (Read 185360 times)

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Offline tatus1969

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Re: kWeld - "Next level" DIY battery spot welder
« Reply #325 on: September 03, 2017, 10:22:58 pm »
I'm curious if I can use this LiTiO (6S):
https://www.ev-power.eu/LTO-technology/Lithium-Titanate-Oxid-Battery-Cell-LTO-2-4V-30AH.html?cur=1

Price may not be competitive but my idea is:
- use 6S LTO battery pack in my car as a secondary battery (should have good cold temperature performance for cold starts)
- make this battery removable from car and use it as a occassional portable powersource (for kWeld...)
- charging would be done in car from alternator
I checked the specs, they say <1mOhm per cell. Whatever that means. If the reality is close to 1mOhm, they would be fine. You would probably charge them to <13V. Current would then be 13/(6+3.3) = 1400A.
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Offline SirJMD

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Re: kWeld - "Next level" DIY battery spot welder
« Reply #326 on: September 04, 2017, 07:46:39 am »
I've heard that the first pulse's purpose is to remove oils and other impurities, so the second pulse can perform the actual weld.

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

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

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

One limitation I've noticed is that the high current makes it difficult, if not impossible, to weld thin wires. They.. vaporize. I'd really like to be able to weld fuse wire, like Tesla uses.
 

Offline tatus1969

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Re: kWeld - "Next level" DIY battery spot welder
« Reply #327 on: September 04, 2017, 09:32:56 am »
One limitation I've noticed is that the high current makes it difficult, if not impossible, to weld thin wires. They.. vaporize. I'd really like to be able to weld fuse wire, like Tesla uses.
The minimum pulse width is 50us, which would result in ~ 0.1 joulses (into 1mOhm). I'll make some tests, but I have the hope that it is just an issue with the minimum adjustable energy (2J). I already had received the suggestion to make the dial knob logarithmic, which would easily enable lowering that limit.
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Offline tatus1969

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Re: kWeld - "Next level" DIY battery spot welder
« Reply #328 on: September 04, 2017, 10:17:55 am »
ops, this is now re-arranged.
thanks for the correction
now even the short battery lead is making quite a ton of voltage spikes
To me this clearly shows the limitations of SPICE when using components this far beyond their ratings. Both voltage peak level and shape aren't even close to reality as shown in the scope screenshot. Thanks for the simulation, and let's continue this way, but at the moment I see my doubts confirmed.
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Offline SirJMD

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Re: kWeld - "Next level" DIY battery spot welder
« Reply #329 on: September 04, 2017, 11:43:37 am »
One limitation I've noticed is that the high current makes it difficult, if not impossible, to weld thin wires. They.. vaporize. I'd really like to be able to weld fuse wire, like Tesla uses.
The minimum pulse width is 50us, which would result in ~ 0.1 joulses (into 1mOhm). I'll make some tests, but I have the hope that it is just an issue with the minimum adjustable energy (2J). I already had received the suggestion to make the dial knob logarithmic, which would easily enable lowering that limit.

Sounds great.

I was actually thinking that a rotary encoder, or simply up/down buttons, would work better than the current dial.
 

Offline anishkgt

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Re: kWeld - &quot;Next level&quot; DIY battery spot welder
« Reply #330 on: September 04, 2017, 12:18:25 pm »
One limitation I've noticed is that the high current makes it difficult, if not impossible, to weld thin wires. They.. vaporize. I'd really like to be able to weld fuse wire, like Tesla uses.
The minimum pulse width is 50us, which would result in ~ 0.1 joulses (into 1mOhm). I'll make some tests, but I have the hope that it is just an issue with the minimum adjustable energy (2J). I already had received the suggestion to make the dial knob logarithmic, which would easily enable lowering that limit.

Sounds great.

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


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Offline tatus1969

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Re: kWeld - "Next level" DIY battery spot welder
« Reply #331 on: September 04, 2017, 12:54:39 pm »
I was actually thinking that a rotary encoder, or simply up/down buttons, would work better than the current dial.
Certainly a rotary encoder would be better than a pot. Can have precise numbers.
On the list :-)
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Online Fraser

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Re: kWeld - "Next level" DIY battery spot welder
« Reply #332 on: September 04, 2017, 03:05:26 pm »
Hi and Lo current range selection, in combination with the pot, should be enough for most battery welding tasks.

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

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

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

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Offline tatus1969

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Re: kWeld - "Next level" DIY battery spot welder
« Reply #333 on: September 06, 2017, 11:38:26 am »
the main "model" that hit the spot is skin effect of the copper @ high freq
I wouldn't be surprised at these high current, but are you sure that skin effect plays a role here? The MOSFET switching time is not very fast, rise time is 7 microseconds. (That is okay for the transistors even at this current level, switching loss is always less than 2000A * 30V * 7us = 0.42J.)

I think that the ~50V constant voltage in the oscilloscope screenshot is mainly caused by avalanche breakdown of the six large MOSFETs. The freewheeling diode does its best but it can only divert a fraction of the current through it. The combined die size of the six MOSFETs is approx 80 mm^2, that of the diode is much smaller.
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Offline tatus1969

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Re: kWeld - "Next level" DIY battery spot welder
« Reply #334 on: September 06, 2017, 12:03:17 pm »
I've got new results from the capacitor based supply. Same basic procedure: repeated 50J pulses into a 1mOhm weld spot resistance. That resistance was a bit high this time (1.3mOhm), and the resulting pulse duration is approx 40ms.

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

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



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



I did some calculations, and a 3S2P configuration will reduce the energy loss per 50J pulse to 113J, which is only one third of what it is now. This will allow my targeted pulse rate of once per second. But how to charge them? I don't really want to go for the additional cost of a 70A step down converter...
« Last Edit: September 06, 2017, 12:10:17 pm by tatus1969 »
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Offline Kjelt

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Re: kWeld - "Next level" DIY battery spot welder
« Reply #335 on: September 06, 2017, 12:23:26 pm »
So how many F's should the caps be for 5S to be ok ? The BCAP0350 are also around €10.- (but higher ESR of 3,2mOhms)
The ones above that double the F's (650) but start to go to three times the price  :(
But is it allowed to just put two strings parallel ? Then 5SP2 would be a mediate option for around €100.- total cost
« Last Edit: September 06, 2017, 12:32:22 pm by Kjelt »
 

Online Fraser

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Re: kWeld - "Next level" DIY battery spot welder
« Reply #336 on: September 06, 2017, 12:29:28 pm »
Yay! My kWeld arrived today  :D

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

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

Fraser
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Offline tatus1969

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Re: kWeld - "Next level" DIY battery spot welder
« Reply #337 on: September 06, 2017, 04:20:00 pm »
So how many F's should the caps be for 5S to be ok ? The BCAP0350 are also around €10.- (but higher ESR of 3,2mOhms)
The ones above that double the F's (650) but start to go to three times the price  :(
But is it allowed to just put two strings parallel ? Then 5SP2 would be a mediate option for around €100.- total cost
A 5S2P configuration would lose 187J per weld pulse. The more cells added in series, the more the losses. I have attached the spreadsheet that I made for my estimations. The 650F model can also be used in place of two BCAP0310, but as you say the price isn't as good. I don't recommend the BCAP0350 because of its higher ESR.

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

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

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Offline wire.rat

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Re: kWeld - "Next level" DIY battery spot welder
« Reply #338 on: September 06, 2017, 04:26:03 pm »
Hi all,

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

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

http://imgur.com/a/N8x5L

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

https://item.taobao.com/item.htm?spm=a230r.1.14.33.76bf5238gg0NQ&id=539313013540&ns=1&abbucket=17#detail
 
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Offline SirJMD

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Re: kWeld - "Next level" DIY battery spot welder
« Reply #339 on: September 09, 2017, 07:22:32 pm »
A bit more testing done. It's possible to weld thin copper wires at 2 joules.

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

 
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Offline romantao

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Re: kWeld - "Next level" DIY battery spot welder
« Reply #340 on: September 11, 2017, 01:14:52 pm »
Hi everyone,

Just wanted to share my recent experience with the Kweld.

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

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

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

The connector and contacts are rated for 120A continuous.

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

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

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

Regards
 
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Offline tatus1969

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Re: kWeld - "Next level" DIY battery spot welder
« Reply #341 on: September 11, 2017, 02:52:36 pm »
A bit more testing done. It's possible to weld thin copper wires at 2 joules.
Sounds good! If you are more interested in lower energies, then I would prepare a logarithmic firmware that goes down to 0.5J (lower values do not make sense because the min pulse width is 50us). You would need to wire up one of these www.ebay.de/itm/252757338778, or buy my programming adapter kit: https://www.kicksurfer.de/index.php/product/kweld-firmware-update-tool/
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Online Fraser

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Re: kWeld - "Next level" DIY battery spot welder
« Reply #342 on: September 11, 2017, 03:24:25 pm »
Romantao,

Nice work  :-+

Fraser
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Offline maukka

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Re: kWeld - "Next level" DIY battery spot welder
« Reply #343 on: September 11, 2017, 03:53:20 pm »
Got mine too and it's working perfectly with the Turnigy nano-tech 3S 5000mAh battery Frank also suggested. First I tried a too overkill of a lipo, which just activated the overcurrent protection (or exploded with sparks and a bang on the electrodes, wife says thanks for the heart attack) during the calibration phase.

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

« Last Edit: September 11, 2017, 03:58:43 pm by maukka »
 
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Offline SirJMD

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Re: kWeld - "Next level" DIY battery spot welder
« Reply #344 on: September 11, 2017, 08:29:47 pm »
A bit more testing done. It's possible to weld thin copper wires at 2 joules.
Sounds good! If you are more interested in lower energies, then I would prepare a logarithmic firmware that goes down to 0.5J (lower values do not make sense because the min pulse width is 50us). You would need to wire up one of these www.ebay.de/itm/252757338778, or buy my programming adapter kit: https://www.kicksurfer.de/index.php/product/kweld-firmware-update-tool/

I think 1 joule might be the sweet spot for the thin wires. 2 joule melted the wire a bit too much.
 
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Online Fraser

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Re: kWeld - "Next level" DIY battery spot welder
« Reply #345 on: September 11, 2017, 08:39:06 pm »
Can the firmware provide a 1 Joule to full power operating range without losing too much resolution ?

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

Fraser
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Offline tatus1969

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Re: kWeld - "Next level" DIY battery spot welder
« Reply #346 on: September 11, 2017, 10:08:18 pm »
Can the firmware provide a 1 Joule to full power operating range without losing too much resolution ?
I'm sure it can, I'll test making the dial behaving exponentially tomorrow. Attached the spreadsheet for the intended formula. First 20%: 7J, then: 19J .. 48J .. 121J .. 304J. At 500J you don't care for milliJoules.

« Last Edit: September 11, 2017, 10:09:54 pm by tatus1969 »
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Offline ovnr

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Re: kWeld - "Next level" DIY battery spot welder
« Reply #347 on: September 11, 2017, 10:52:37 pm »
Tatus: I haven't kept up with the thread as much as I probably should have, but any plans for another batch of kWelds?
I wanted one, but had already spent a bit too much money on other frivolous things that month.
 

Offline ozwolf

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Re: kWeld - "Next level" DIY battery spot welder
« Reply #348 on: September 11, 2017, 10:58:42 pm »
Tatus: I haven't kept up with the thread as much as I probably should have, but any plans for another batch of kWelds?
I wanted one, but had already spent a bit too much money on other frivolous things that month.

Same here...
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Offline HackedFridgeMagnet

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Re: kWeld - "Next level" DIY battery spot welder
« Reply #349 on: September 11, 2017, 11:07:16 pm »
+1 for me
 


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