Capacitive welder build - A bit more serious approach

Hi, I know im a couple months late to the question and you probably have an answer but to mount the electrodes I use

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How is this project coming? Did we decide that the easiest way to implement this was with a 2F supercap and simply load it up to the voltage that gives you the weld profile you want? I’m not having much luck with my Sunkko 788, it seems to poop out after about the 4th weld, and I’m loathe to invest in a 709 as they are getting bad reviews.

Have we coalesced on this as the best method?

and if I’m reading this right, I can get 10 3.3F 2.7V supercaps for $10?

The only thing I can think is maybe the leads aren’t big enough, but from the picture they look pretty beefy.

Or am I missing something?

10 of those caps could store enough energy for even heavy welds, but I suspect you’re going to be HEAVILY limited in your performance by the internal ESR of those caps. The can is very small at 8mm dia x 20 mm length so I looked for an equivalent sized and rated superCap at Digi-Key and found the following brand name capacitor

https://www.digikey.fi/product-detail/en/eaton-electronics-division/HV0820-2R7305-R/283-4197-ND/3878077

It’s pretty much the same size at 8mm dia x 21 mm length and rated for 3F @ 2,7 Volts. So essentially this is direct apples to apples comparison.

The datasheet shows the ESR to be 80mOhm with the rated pulse current of only 3,3 Amps. THIS IS A TERRIBLE CHOICE FOR YOUR APPLICATION. You’re not going to get enough current from these to make any sort of welds. In capacitive welding, your capacitors are everything, if you can’t put in the front cost of buying enough big caps, your welder is going to underperform.

I’d recommend you go for the Li-Po welder solution if you’re tight on money. It’ll perform better for lower price even if it might not be as long lived as a much bigger, heavier and costlier proper capacitive welder.

Thanks SimosMCmuffin! This is exactly the feedback I was looking for. I don’t mind spending the money on good caps - I just want the thing to work.

If you were going to choose a set of perfect supercaps for the job what would they be?

Is rated pulse current the most important thing? For instance, this one’s rated pulse current is 61A, but since there will be 10 of them in series I guess that’s my max for the pack.

Should I be looking for more than that? and should I be looking for an ESR above a certain number? The above is 0.012 ohms.