in short, how do i de-rate this stuff?
I figure I can control voltage to control the weld with fidelity rather then using a pass switch and just short it out with something like a copper rod I bang into a plate
I think so long the surface is good clean and degreased with its fixtured there is no reason that more advanced control then capacitor voltage is necessary?
Okay heres what I know. I'm answering because nobody else has, although I don't know how much this will help.
I needed a quick and dirt li-ion tab spot welder, years ago. I found this site and built it accordingly. It worked great for hundreds and hundreds of tabs.
https://www.philpem.me.uk/elec/welder/That said, it was only 0.6F total. Yours would be 4000F?
I think the esr of my caps is probably about 10m ohm and I used it at around 10V?
If your cap ESRs are 20 times less and your capacitance is 6000 times more, I think there may be an issue here with too much energy going to the weld, since our end-applications were the same.
Here I'll take a stab at making it all equal:
Energy mine dissipated at 10V = 0.5 * 0.6F * 10^2 = 30J
To get your 4000F to the same energy.. 30J / (0.5 * 4000) = voltage ^2 = 0.122V ?
And maybe we can just say the ESR doesn't matter because the time scale is very short for the weld to take place and the weld resistance dominates anyway (hand waving here)
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