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Large electrolytic cost/size "sweet spot"? Answered

I'm in the process of sourcing components to build a capacitive discharge battery tab welder - there are a few designs out there on the internet from this one: http://www.philpem.me.uk/elec/welder/ which I like because it's nice and simple, to this one, http://www.youtube.com/watch?v=hxWo8ko2k2A which is gorgeous but complicated. So anyway, first off I want to find some large capacitors. I'm wary of using car audio stiffening capacitors as it looks like they don't last very long for this purpose, although they can be obtained relatively cheaply, and I can't afford large standard type electrolytics which cost an arm and a leg.

I did have the idea that there must be a "sweet spot" in terms of cost/size where I can build a bank of capacitors without breaking the other sort of bank - it looks like probably being around the 20 x 47,000uF (like this design uses: http://www.pittnerovi.com/jiri/hobby/electronics/welder/index.html ) mark, but I wonder if anyone with more recent component purchasing experience than me can provide some pointers? The voltage rating needs to be in the 20 to 30 volt range.

Oh, and when I've finally built one, I'll post an instructable, I promise! My version is likely to be rather more analogue though as I don't know anything about microcontrollers.....


Also, try to source from surplus wherever possible, you get stuff at 10 cents on the dollar.

Get PCB mount ones - we were looking at work todat for one of our PSUs, and PCB mount were 1/3rd the price of chassis mounts