I feel like it makes less of a difference the better you are at soldering and with higher wattage irons. Either way, I prep my nickel like you if I remember to
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I never pre-solder the nickel, but it definitely is a good idea. Especially if your soldering capabilities are questionable.
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This, 100%
I generally give advice assuming that the person reading has zero skill, because thatâs the worst case scenario. So I try to give best practice tips that will make their work marginally safer, even if those tips are not always worthwhile for more experienced builders.
Especially for soldering, because thatâs such a fiddly skill. Some people can solder for years and never really get the hang of it, some people can pick it up in a weekend. Itâs pretty much impossible to gauge someoneâs soldering skills without inspecting a lot of their work.
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Thats why we love you duck man.
Has anyone ever told you it might be a good idea to write a battery building tutorial?
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Itâs come up a time or two 
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how much of the negative needs to be covered? if i cover 2/3 roughly of it with nickel (folding 25mm strip over the side) then will that be enough?
How much of the negative is covered really doesnât matter. What matters is that the strip is welded well enough to the negative (for the amount of current you want the welds to carry) without any welds in the middle 3mm of the negative end.
Some can can do a great set of welds when only covering half the negative. Others need, or prefer, to cover the negative end completely. Youâll have to decide based on your welding skills.
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i managed to get 6 welds (2x3) fine without touching the middle
i am only covering a half to 2/3 of the negative so just making sure that isnt the bottleneck
Heat generated goes up by a factor of current squared, not linearly with current, so youâre getting ~16x less heat in a LOT more thermal mass to absorb it and surface area to expel it. On top of that, the electrical and thermal properties get a bit funky when youâre at those extremes of current and (in the case of spot welders) temperature
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I was absolutely salivating over a big tungsten electrode one that can spot weld copper instead of nickel a while ago but as you said, insanely expensive
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They do look like theyâll hold. But the upper one is better than the lower one, and ideally you want the solder edges to blend to the nickel not form a bubble that cuts back at the nickel
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I agree with @A13XR3, the solder should transition smoothly down to the nickel and not appear to be just sitting on top of it. It should be a shallow ramp of solder up to the wire and not a sudden bead of it.
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Yep, getting better. Make a wider solder prep area for the wire to be soldered too. I presolder a little pool about double the width of the wire end.
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Great idea. Thank you
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Top right one looks good! If youâre able to go hotter (canât remember if the recommended iron was a TS100, if so it canât do it without modded firmware) then Iâd go for that, itâs a big lump of wire rather than sensitive electronics. The lithium only really cares about the total amount of heat that gets transferred into it, so itâs basically sensitive to duration of soldering rather than temp of the iron and higher temps will get the job done faster.
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I did some tests of solder to nickel, trying a smooth untouched surface, a scratched/sanded surface, and different blob sizes.
So far what I encountered was that thereâs very little difference between adhesion, so long as the joint/surface was properly wetted with the correct heat and flux was used.
They pulled off about the same, all taking a good amount of force and rolling the nickel away with two pliers to actually remove it. And even then in each case, there was still a layer of solder on the nickel surface that peeled off the foot of the solder blob.
Iâll make a couple video clips over the weekend to show what I mean.
Either way, it set at ease my worry of most solder joints on the nickel.
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