I saw in a lot of youtube videos people using capacitors connected in parallel to make use of the current for a spot welder for battery tabs, I was checking my cemetery box last night and found a lot (like 60) Li ion 18650C4 batteries, they are rated for 2200mA and 4.2V nominal, I think that's a lot, if I put 60 of them in parallel, now, I'm worried for the stress I would be imposing on the bank, perhaps a low resistance high wattage lamp would alleviate the near zero resistance at the end? or is this a no no, don't do it project? I can also use them for other things, like a battery powered mini car for my kids, but what I need right now is a spot welder for fixing laptop batteries in my computer shop at the end of the world :) , I have no trouble charging them and I have been using batteries for a long time charging and discharging them with a constant current charger and limited voltage power supply, plus a temperature sensor, just in case.

  • \$\begingroup\$ I suspect that people use capacitor banks for sudden current requirement for the spot welder. I don't know that a battery than provide 200A(?) safely without heating up. \$\endgroup\$
    – ammar.cma
    Sep 24 '16 at 19:29
  • \$\begingroup\$ Any car battery can provide several times that. Safety requires some thought though, with more than one way to break the circuit if anything goes wrong. \$\endgroup\$ Sep 24 '16 at 20:27
  • \$\begingroup\$ 60 2.2Ah Li-ion cells will easily do 200A (that's only ~3A per cell or 1.5C), they'll probably push 600A total (10C) if you're not careful. For comparison, I've tested a 90C turnigy nanotech li-po at 750A short circuit and that's about the size of just two 18650 cells. Lithium batteries can supply ridiculous amounts of current for a few seconds - although it probably doesn't help their lifespan much though. \$\endgroup\$
    – Sam
    Sep 24 '16 at 22:13
  • 1
    \$\begingroup\$ AvE on youtube is currently doing exactly this, with a solenoid to control the time. It seems to work quite well: youtube.com/watch?v=UU7QC5Uby6M \$\endgroup\$
    – 0xDBFB7
    Sep 24 '16 at 22:55
  • \$\begingroup\$ Do you know how much voltage is needed to spot-weld? Is 4V enough? You might need to add an inductor in series. \$\endgroup\$
    – mkeith
    Sep 26 '16 at 1:40

Fixing batteries with a spotwelder is frequently done with large capacitor banks. The capacitorbank solves two problems at the same time.

  1. During spotwelding (for fixing a battery cell) a large to very large current is available.
  2. In case something goes wrong (when fixing a battery cell) the large current is reduced to low when the capacitors are discharged.

With a large battery made of Li-Ion cells you would be able to reach target 1.

However when something goes wrong this battery would keep on supplying large currents. That would form a large risk in terms of fire hazard. For me is therefore a DONT.

  • \$\begingroup\$ Plus there is no risk of running the caps by deep discharging it, unlike the batteries. AFAIK \$\endgroup\$
    – Passerby
    Sep 24 '16 at 23:55
  • \$\begingroup\$ Thank you for the advice @Decapod anyways don't forget this is not for a production environment, just home use, I was mostly worried for the battery bank, and all the comments from other guys helped, so I'll give it a try, with your safety warning present, of course. \$\endgroup\$ Sep 26 '16 at 23:55
  • \$\begingroup\$ If you are happy with my answer please upvote and/ or accept. \$\endgroup\$
    – Decapod
    Sep 27 '16 at 5:35

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