Trivial capacitor based battery tab welding machine

[pereczes]

another research I was doing was about welding tabs to a li-ion battery. Soldering seems to be difficult due to dangers of over-heating. Remember when I was kid was discharging capacitors, low charge ones and two metal thingies were sticking together from the spark energy.

Wonder if that would be possible with a high 100F capacitor to stick a nickel tab to the battery.
Found another thread here and tons of videos with over-engineered devices and tools.

for me the idea is to load the capacitor and the booom (hopefully not my head )

[calexanian]

Typically capacitor discharge welders for battery tabs use a step down transformer to generate high current and switch on the high voltage side. It's very common. Just you tube videos of battery tab welders. I built my own out of a big variac and a harbor freight spot welder with a foot pedal to close the jaws and some bending of some micro welder electrode rods.

[Rerouter]

Most of them rely on voltage rather than capacitance to make the massive currents necessary, on i worked on a few months back had a voltage control know and a trigger button on a lead, it charged up the capacitor bank with a SCR rectifier, so that it would stop charging once past set point, then when you hit the trigger circuit, some active device would shunt the capacitor array across the 2 leads

[GeoffS]

A couple of DIY designs for capacitive discharge welders

https://ultrakeet.com.au/write-ups/cdWelder

http://frikkieg.blogspot.com.au/

[Rerouter]

I would strongly recommend even a crude trigger circuit, so you can get things in place, nice and firm and then hit to weld, i would not want dangerous voltages constantly on the wires, and tapping to zap will burn the surface more than weld,

[SArepairman]

Ah you guys gave me the idea to modify my home made optional isolation variac box to be modified with a switch that disconnects mains and connects the mains input through additional connectors on the front panel so I can hook up a capacitor and use it as a spot welder. good idea?

what voltage/capacity capacitor did you use for yoour variac spot welder?

could I use a 10000uF capacitor charged to 170V discharged through a variac?

how good of a pulse circuit do you need? I'd prefer a low tech momentary contact switch solution.

[ion]

Well, you can't get much simpler than this: http://ledhacks.com/power/battery_tab_welder.htm

Just make sure to somehow disconnect the power supply before you trigger the SCR.  IIRC there's a note somewhere on that site that  leaving it connected eventually caused the power supply to fail.

[calexanian]

The more I use my home made AC welder the more I like it. I use a 10 amp variac with it, typically at about 60 to 70 volts for nickel strip of the sort used for battery ribbon and its happy. I have it rigged up to a foot pedal that closes the jaws and hits a switch and applies power. Very handy for all sorts of things. I use it primarily for my vacuum tube hobby stuff but i find myself using it for all manner of other things around the shop.