Kweld welder setting for different cell types

I have just acquired a KWELD welder and their Kcap capacitor bank.

I am interested in what power settings people are using to create good weld results.

Of course this depends on the actual cell type and manufacturer and the thickness and metallurgy of the connector strips.

Would appreciate people sharing what combinations have worked well.

I start with 2 pieces of scrap nickel strip of the same thickness I am going to use on the cells and adjust the setting til I have to use pliers to rip them apart and part of the nickel rips a hole is a good starting point. Then I take a battery cell that I can practice on to get the settings correct, preferably a dead one, but definitely the same that I am going to use for the pack. It should take pliers to pull it off and should leave a piece of nickel on the battery cell. I suggest using the negative side of the battery for this.

I usually start around 20J and work my way up, but I am using LiPo batteries to power my KWeld, so your settings might be different.

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Thanks for the info - very helpful. I’ve watched a bunch of videos and have used a large welder quite a bit so understand the need for the metal pieces to be fully fused but I won’t have any dead cells to practice on.

I will be making pack(s) out of new
LG INR21700M50LT cells

so with a cell holding even less than full charge and perforating the cell “container” things might get interesting. :grinning: I plan on doing the testing outside just in case!

I’m not sure the capacitor bank between the power supply (battery in your case) and the welder actually effects the welding “pulse” assuming the battery has a good charge on it. From my understanding the KCAP capacitor bank ensures the welder gets the same amount of power for each weld ensuring consistency. I’m not sure I needed the KCAP other than it will let me use a small amperage bench power supply I have as the initial power supply.

Dont stress it too much. It really isn’t too difficult and the KWeld is a great piece of kit and provides very consistent results. Just make sure you put the little donut rings on the positive side and take your time double checking which cells you are connecting together. Make sure your work space is clean and keep a good fire extinguisher nearby. I was super nervous the first time I built a pack. I am more comfortable after building a few, but I still check everything multiple times and cover any cells that im not working on in either fish paper or kaptans tape to avoid inadvertently shorting any cells.

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How thick is the strip you are welding to the cell at 20 joules?

I am using .2mm pure nickel strip. I usually end up welding at 30-35J, but I start my testing at 20J just to test/verify.

I will try and put together a quick video just demonstrating how I do it. I’ll try to get it to you by Friday.

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Thanks for the feedback and vid offer. I’ll take whatever help is offered.

I bought some of each of these when I ordered welder so will modify your numbers by the applicable percentages that should get me in the right neighborhood.

IMG_2093

No rush for vid as I have a good pack now and am thinking of the new packs as a project for when the temps drop here and the water gets hard :grinning:

I have some .15mm I can demo on for you.

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I took a sacrificial cell, .2mm nickel strip and pliers and ran lots of shear rip tests, I ended up higher like 50j on my build

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I also used 0.2mm nickel strips with Molicel P42A and Samsung 40T cells. For both I set energy between 48 and 50J. Welded with a Lipo@1200A. The first battery is from spring 21 and the welds still hold after the 3rd season. The chosen energy was based on tests and experience from someone who built several batteries with kweld. Definitely do some tests, I always order one or two spare cells for this purpose.

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Why choose negative?
The negative has contact to the jelly roll, but the positive is towards the vent, so if you blow a hole on the negative the cell is dead, on the positive it doesn’t matter so much.

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I took 22J for 0.15mm nickel and LG M50LT.
For 0.2mm I have 25J and for 0.3 I think it was 36J.
Of course, this can be different for you, so take it slowly.

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Honestly, no reason other than I find it easier.

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So same cells that I have. :+1:

Just a general question to the forum:

I’m not clear about the amp range for each thickness and how much leeway there is for optimal performance and safety.

So far there have been three thickness options mentioned

0.15
0.20
0.30

I plan on 12S11P packs of the 50MLT cells. I purchased several never used 10S11P packs that were made for robots so after I remove the current packaging I end up with a lot of the welding work already done😀 I hope.

I hope to just add on 2S to those packs but I’m thinking perhaps I should ensure that I match the thickness of what is already done when I’m adding cells???

Again any help is appreciated

I would personally just use the same size that the packs already have.

I have tried to research all the amp rating stuff without much faith in the numbers. Hopefully someone smarter than me will chime in.

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Check @ludwig_bre cell connection heating calc sheet uploaded here, that’s the best effort i’ve seen.

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The @ludwig_bre calculator: Battery Pack Nickel Strip Calculator

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I finally found time to assemble my welder, Kcap and housings so that I could confirm that it’s fully operational.

I used a bench power supply set to 8.2V - 10A to charge the KCap. It took a few minutes before the welder “woke up” so that I could calibrate and try some test welds.

I did 4 welds to connect two strips of 0.15mm nickel 2 at 10J one at 15J and the last at 20J. They all seemed fairly solid but it’s clear that a 5J increment makes a difference in “penetration”

I then powered off the PS and did 15 more welds at 20J to try to “drain” the KCap. I stopped and let it sit for 30min or so and then tried a 16th weld and got an undercurrent error.

So successful test that confirmed that this is quality gear!!

I do have a use question though. If anyone is using the Kcap module how do you completely
drain the bank for long term storage?

Right now I can’t do any more welds but the led screen on the welder remains lit and the circuit board leds are still on indicating power remains in the Kcap bank.

How are these $25 welders from Aliexpress?

Don’t understand what your asking??