wow
i see you have 10 welds is that normal or is 6 that i am doing fine?
thanks
6 seems to standard practice (take that with a grain of salt). But with the sheer amount of available space on 21700s it’s nice to squeeze in a few more.
I think it might have been @ZachTetra mentioned a while ago that each set of good welds is good to carry 5a? Would like a refresher on the science here if you wouldn’t mind please Zach
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ah i see
i try to do 6 good welds but often i end up less
i always make sure to have at least 4 spark free and good ones on each cap
plus since i double stack nickel i suppose the welds on top help a bit to
I believe each dot is good for 5A, and each pair 10A.
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K. So 4 good + 2 bad for 25 burst? (Thats on the worst cells)
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I was thinking about this for a while after reading it, and I think I know what the science is.
If you think about it, the weld is probably limited by the steel can side, not the nickel side. If we reference the conductor current rating sheet,
9.8A of current through steel can be poorly carried by a strip 0.3mm x 7mm, which has a cross section of 2.1mm^2. This is about 4.67A per 1mm^2 of steel. If we look at the size of a weld, I measured about 1.1-1.2mm in diameter, which has an area of around ~1.1mm^2. So 1.1mm^2 of steel multiplied by 4.67A = ~5.13A. I figured the poor/hot number made sense as the 5A rating for a weld was a max.
This is just a hypothesis and could be completely wrong.
One thing I noticed is when you compare it to the other current ratings of steel strip, it does not really scale. Seems like the bigger the strip, the ampacity increases is nonlinearly. Maybe because of different heat dissipation or something.
Also the area of a circle calculation for a weld is radius squared so it can vary a lot based on weld quality. A 1mm diameter weld is only good for 4A based on this, but a 1.3mm diameter weld can do 6.25A.
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maybe a stupid question but what is bad about a hot weld? also is it better your welds are a little hotter then they should be or a little colder?
i need 30mm wide nickel and have 25mm
is it unreasonable to suggest spot welding 2 pieces together to create a 30-35mm piece?
So my welds have always gone on great. Not too hot, not too cold. I adjust them when needed as the battery gets lower and such.
The problem that has been confusing me like crazy is my welding tips… Ever since the first few welds, I noticed the positive end will almost always stick or leave a speck of copper. After every thousand welds or so, I have to sharpen the tip all over again as it wears down too flat to make a reasonable weld without increasing power. The negative end has not had any issues at all, retaining its perfect original finish until ~8000 welds. At that point the hot tip touched some plastic and melted over the whole tip.
After sharpening both the same way, The positive end is the only one that continues to stick or leave copper deposits on top of a weld.This shows that it was not due to me keeping the negative tip factory cut. I have yet to try and swap the cables, but it has been bugging me the more that I think about it.
at almost 14000 welds, my positive tip is now half the size of my black tip which has only been filed once to remove plastic.
Is that normal?
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Joey has the exact right idea, the rule of thumb I currently use is 5A per single weld point, and 0.1mm^2 of nickel cross section per amp flowing normal to it. Good practice supports having your welds spaced as far out as possible in the given space. It’s possible to get 8 welds on a positive terminal by doing 2 rotated diamonds. Also limit negative welds to the perimeter of the can if at all possible
This is a half saturated weld pattern, but the pack is only pushing 20A total so realistically I can just do a single point but I use a minimum of 4 for integrity (4 for bricks/bikes/scooters, 6 for flex packs)
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I didn’t know this…good info!! thx
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anyone know as im out of 30mm nickel with 3 p groups to go
If you mean “weld” by “solder together before attaching to cells” I feel like there’s a better chance of working well, but the best idea is to pause construction and get more nickel.
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Yes. Is it also annoying as hell? Yes.
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solder is prob a good idea
issue is no where in the uk sells pure 30mm nickle
i only need for the pos as for the neg i can get away with 25mm
litterally just need 1-2m of it
i believe @glyphiks did it once to weld pieces of nickel together
If you do solder them, just make sure you don’t weld over the soldered area.
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I may have some you can have leme check and get back to you,
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thanks man litterally need a teeny bit and will happilly pay the cost for you to buy more
if necessary got some 15mm so i can just do single strips and then connect the 2 halves with it also
99% I cant get you some, how much do you think you need 30cm? 1m? just so i have a rough idea
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