0
\$\begingroup\$

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.

\$\endgroup\$
  • \$\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\$ – Brian Drummond 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
1
\$\begingroup\$

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.

\$\endgroup\$
  • \$\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\$ – ortegacomputacion 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

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.