Congrats on the sales... glad I ordered when I did.
Been on the look out for some super capacitors with extremely low ESR (Kinda funny considering I almost don't even care about the Farads for the most part, tho seems like with super caps the higher the F the lower the ESR). I think I found a good solution... especially for you, since I think they are located in Germany (haven't checked shipping rates to the US yet). The company Skeleton Technologies makes a handful of super capacitors with the lower ESR's I've seen. In general, I haven;t been able to find any capacitors with lower than 2mOhm ESR for under $50 each (at least non in stock, and usually closer to $60 each)... that was until now. The downside is, depending on which capacitors, would either have to order a box of 20, or a box of 10 (the larger ones are sold in 10's). But this wouldn't be so bad if a few people wanted to go in... I'm thinking pretty much any of these could be ran in a 3S1P config, and produce the power we were hoping for, especially the 1200F+ models.
For a quick summary of the models, there are 5, all of them are rated at 2.85V ( a little step up from the usual 2.7V):
Code: Select all
Model Farads ESR(mOhm) Price(box) Qty Price/1
SF0500 500 0.23* 412.00 € 20 20.60 €**
SF0750 750 0.21* 596.00 € 20 29.80 €**
SF1200 1200 0.11* 340.00 € 10 34.00 €**
SF1800 1800 0.10* 370.00 € 10 37.00 €**
SF3200 3200 0.09* 480.00 € 10 48.00 €**
* I used the "typical" <10ms DC ESR from the datasheet (which is the lowest value given, but likely the most relevant for this situation)
** I didn't look into shipping yet, I figure that depends on where they are being shipped (I'm assuming cheaper to Germany than the US), and this price is just for reference, haven't really found these for sale as singles, other than 1 on amazon that wasn't exactly cheap.
BTW, the "initial capacitance" is actually 5-10% higher than the ratings I listed (but as I mentioned earlier, I don't think the actual capacitance is that important for this.... of course we need enough to do a good amount of welds, but I'm pretty sure that's not even a concern with this high capacitance... PLUS, if I'm not mistaken, it's theoretically possible to have these charging during use... tho probably not very necessary)
Anyway, I figure either the SF0500's or even better the SF1800's (I figure it's with the $3 more than the SF1200) could be viable Super Capacitors to use in a 3S1P config most likely, and a little cheaper than others I've seen, with even lower ESR, and the extra .15V each doesn't hurt. Of course would have to get at least a box, but based on how quickly you're selling the welders, I'd be willing to bet there's enough of us to go through a few boxes. Though, one possible design flaw that may make these significantly less viable, is their terminal's... or almost, lack there of any. They appear to be similar to the positive ends of a button cap battery, which I'm assuming is far from ideal. I'd much rather have a pair of screw terminals on the same side, if possible.
Here's a link to Skeletontech's web store: https://www.skeletontech.com/ultracapacitor-webstore
And here's the datasheet: https://cdn2.hubspot.net/hubfs/1188159/ ... et-SCA.pdf
I've also been admiring the design this guy used: http://www.zeva.com.au/Projects/SpotWelderV2/
It would be very interesting to implement something similar to his (especially if I found a viable smaller capacitor... probably wouldn't make as much sense for large super caps like these). The core concept tho, having individual "break-away" PCBs with a number of small capacitors in series, and the MOSFETs to handle their power on each board... where it would essentially be up to the user to decide on how many of these to chain together (essentially put in parallel) to fit their power needs. Definitely seems like a cool concept, especially since you'd be able to add another board in if what you currently had wasn't doing the job. This kind of design wouldn't be too hard to accomplish with the more stereotypical android controlled welder, where the user sets pulse times, etc.... but I'm not sure how easy it would be to setup to work like your design. But it would be interesting if that could work... if you made your core control board capable of being hooked up to something like this (instead of just having the power source as changeable, having the mosfets as well). I just like the modular design, and the concept that it's almost infinitely expandable.... woudl even be cooler if their was an easy way to make each individual series of capacitors have an optional number in series (ie. be able to run 3 or 4 caps in series, depending on your needs)... basically having it so that the user could leave a spot empty (of course uniformly on all parallel boards), to add 1 more level of customization.
Anyway, I'm probably thinking too far... but jsut a simple 3S1P solution with any of the Skeletontech super capacitors could work out as a pretty sweet power solution for a welder, and so far, it's the cheapest solution I can find to create this high amount of power in short bursts (Tho technically, this thing could produce quite a bit even continuously... though I could only imagine that would require some serious cooling needs... also not something required for this kind of project).