I just built my kWeld and started testing it, I’m planning on starting actual battery building over weekend. I tried welding together few 0.2mm strips starting with 50J which gave me pretty nice welds but they were still possible to rip with my bare hands if I tried, 60J gave me stronger welds I could maybe rip them with my bare hands if i had longer strips but for my small scale I had to use the pliers.
So how strong do welds actually have to be so they wont separate due to vibrations? And on the other hand, if I set it too high can it actually damage cells and if so is there any way to tell if I’m at the safe levels?
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they should be so strong that when they are pulled off, they tear the parent nickel and leave holes in the strip.
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Is welding 2 nickel strips together different from welding nickel onto the cell though? Because welds I make trying to weld 0.2mm strips together are not strong enough to rip strips even on 80J setting they just leave indents. Possibly my power source is not beefy enough? (S4P1 6750mAh 60C lipo)
Hmmm, okay it’s a skill issue, because I was able to make a few very strong welds even on 50J but I can’t figure out exactly what I do different other than put less pressure on electrodes
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More power can definitely help, because it’s not just about the amount of energy you put into the weld (joules), but also how fast you can put that energy in. If you can deliver 50 joules in say 20ms instead of 35, then the center of the weld nugget will get hotter because there’s less time for the heat to be conducted away into the surrounding material.
Electrode placement/spacing, shape, and pressure all play a role too. Pressing too hard is bad, as is having electrodes that are too sharp or too dull. The farther apart the electrodes are, the higher the resistance, which can lower the power.
One thing that can help is slitting the nickel, and placing the electrodes on either side of the slit. This forces all the current to go down through the nickel, through the cell, and then back up, rather than some of it just going through the nickel and avoiding the weld zone.
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50J seems high. I get away with 25J on 0.15mm nickel strips with my kWeld. When I try to pry the nickel strips off, they tear and leave nickel shards on the welds.
Then again, I have yet to get my technique right to avoid sparks (it doesn’t every time now though).
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I noticed that people test welds welding nickel to box cutter blades and so I tried that and lo and behold even at 25J welds were tough and ripped nickel when removed. So now I’m kinda confused what made it so much better, was it the material of the blade? Or its stiffness in comparison to two strips welded on silicon matt?
From left to right 25J,30J, 35J, 40J, 50J
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Kweld with 0.2 nickel and 50J - I had to disassemble an old pack and the nickel was a bitch to tear off.
Using kCap thou, maybe it’s your power source?
I don’t know why people use blades (maybe they don’t have any dead cells to practice on?)
Old or dead cells are the best thing to use for checking energy settings before u start on a pack.
I’m using a 3s 15ah lipo with an imaginary C rating. Recently used it at 50j on 0.2 nickel. Felt good to me.
Zeee Premium Series 3S Lipo Battery 15000mAh 11.1V 100C Soft Case RC Battery EC5 Connector with Metal Plates for RC Car Truck Tank Racing Hobby Models Amazon.com
Don’t get any wild ideas about sharpening new probes. The kweld ones are fancy beryllium copper. They don’t wear down like cheaper probes do.
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Truth. Took me forever to figure this out.
Am I the only fool running a kweld on a deep cycle marine battery?
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For the record I use 50-55J on the negative side of cells with 0.2mm nickel and 35-45J on the positive side. I gave a range because tip dullness / probe temperature changes as you weld so you might want to adjust slightly as you go so that all the welds look more or less the same.
(Source: https://www.researchgate.net/publication/322394238_Parametric_Study_of_Spot_Welding_between_Li-ion_Battery_Cells_and_Sheet_Metal_Connectors )
If you can see the spot welds already tearing off the nickel strip / showing cracks, then the welding time / power was too high.
Holding the probes at a slight angle (like 15 degrees) is good for a more consistent weld surface area.
Note that due to the reflectivity of the metal, pictures you take of your welds and share to others will look way worse than they do to the naked eye.
A tear test with pliers on real cells is the best way to test your welds. The strip should not come off without leaving nickel strands on the cell where the welds were.
Also – since it is the resistance of the contact points that creates heat that melts the nickel to the cell, cleaning your cells and nickel with isopropyl alcohol might actually yield worse results than not cleaning them. Same goes with probe pressure – you really don’t want too much. This is why it’s so hard to automate the spot-welding process to a robot 
@Mordraug if you’re in the US and need some dead cells to test on I have some I can send your way for just the shipping cost. They’re from a battery that I used too much to the point the cell voltage was dropping bellow 3.6 v. They’ve just been sitting under my bed still in a battery shape and have been unused for 3 years or more.
I’ve got more cells that are potentially less stable that I can use for practice in the future so I don’t really need to keep all of them anyway.
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I wish I couldn’t make the same offer.
I’m kind of a free spirit, prefer the small rigs that I could put In my back pocket if my Mom didn’t donate my JNCO’s to goodwill.
Spot welding shouldn’t be locked caged in a garage. We should be free to work a pack whenever we feel inspired, like on the beach, in a library, or at the warped tour when Sun 41 plays ‘fatlip’.
Coincidently, I’m set up to do a little welding.
which is why I figured out that my boat battery and the kweld would fit neatly inside the case for this really expensive Sunstone I got at a discount several years ago but that couldn’t weld anywhere near as reliably as the kweld. At some point I’m going to pack it all in there along with the battery tender and have a cordless Sunstone mod. All it needs is a handle bolted to the top. It would be heavy, but portable.
but for now it is very much just on my bench. Fortunately not in the garage anymore, I’ve moved inside.
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Unfortunately I’m from Poland, I’ll ask some people from my local PEV groups if they have some I could get
I tried it on the old 18650 and welds held decently (I think… when I tried to rip them off with pliers they left behind those buttons of nickel that I had to scrape of with chisel) so I decided to go with it
How bad are these? I tried to avoid centers on negative terminals but I’m not sure if they are not overcooked
Look a bit too hot, you can kinda see the nickel already cracking in places. Still usable though. Also hodling the probes at a slight angle (like 15 degrees) makes for decent welds due to the larger contact area.
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Agreed with Rusins - A bit hot, but serviceable.
Doubling up on your welder batteries will almost certainly improve things by allowing you to get better welds for less energy, and resulting in less heat affected zone around the weld nuggets.
Also using the shortest, fattest cables you possibly can, which reduces losses and further improves maximum power.
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I’m going to practice a bit more on my old cell, it’s a bit tricky as all the stuff like energy, pressure, distance and even angle of electrodes seem to make a big difference. I saw some people use like the 3d-printed holder for electrodes, maybe that will make it easier to make more repeatable welds, thank you very much!