Building 18650 pack - Trouble spot welding negative end

ESK8 Electronics
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I’ve started spot welding my battery pack and the positive side spot welding has gone really well. Good strong welds. I did some tests on spare cells on the negative end and I can’t get a good weld. I’ve turned up the time but I don’t seem to be getting a better weld.

Anyone got any tips for welding the negative end? Do you prep it by sanding or anything? I might need to re-wire my spot welder IMG_20181227_133916 as I tried joining two pieces of 16mm2 cable and I think the join is bottle necking it.

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moved to esk8 electronics :slight_smile:

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ask @bigben or @hyperIon1 they might be able to help out

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@rojitor might also know

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I don’t sand the terminals. Clean and flat work well. How have you joined the cables?

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I had similar trouble when I was spot welding my cells in parallel the other day. Positive side went fine after initial tinkering. Negative side kept giving me trouble. I’m not entirely sure that the welds are good enough to pass a strict criteria but I think they are fine. What I had to do to make them better, because just amping it up wasn’t enough, was upping the multi-stage multiplier. Or reference, I’m using boss level spot welder.

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Not trying to sound corrective, but @hyperIon2 is the one we should be linking, I’ve been doing it too! :joy:

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You could be right about the join.

I had similar issues with my homebuilt welder. Some things I’d suggest:

  • Sharpening the tips of the welding pen - I found mine started to blunt and maybe even oxidise? What are you using for the tips?
  • Shorten the leads from the welder to the pens
  • Are you using a transformer? Do an extra coil of wire around the transformer - this increases the voltage
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To make the join I just meshed the cable together and tried to solder as much as I could, but my soldering iron isn’t very powerful. I’ve ordered a longer length cable to rewire the whole transformer. I’ve been using copper clout nails as my probes

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Cool, same as me. I ended up filing mine to a sharp point every 20 or so welds. If you weren’t already doing that it sounds like yours held up better than mine. Maybe just try changing to some fresh nails?

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I’ll try that. I’ve also order a strip of 60A choc blocks, I’ve currently been using the 30A ones and they get pretty hot after a dozen welds in short time.

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Lead length and your tip are usually the issue.

Even in factory made welders oxidation and heat will corrode and flatten your points. A little sandpaper should keep it clean. Heat will also effect your welds. Keeping everything cool will help. Even a fan on the trans will do the trick.

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Thanks everyone, when the new parts come in I’ll keep them all in mind.

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Parts arrived and I’ve rewired the transformer. It’s comfortably spot welding nickel to nickel now with a fraction of time it previously required so it appears as though the power has jumped significantly. I’ll be getting back to the spot welding over the weekend weather permitting, I’ll be doing it outside in case I burst a cell.

Thanks for the help everyone!

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