That is only true if the useage currents and period allow the leakage to self balance the, in this case I do plan to use them in my Corvair EV conversion project, where the charge/discharge currents will be paralled with the batteries, and modestly high.
For use in EV projects, the Maxwell caps MUST have an active balancing network, as just the variance in capacitance will take the caps over voltage if you attempt to use most of their capacity.
At EV currents the balancing network actually has to be active, to shunt the current past any cap that reaches capacity (limiting voltage). Until then, the shuts are only drawing marginal leakage currents.
Dang .... it's two Jewels, make a JimFart ;)
Well, if you really want to store energy, do it with a high voltage. You can get dozens of Hi-V flash caps for free from "One-use" cameras from your local photo-processors. Sometimes they even still have an alkaline AA cell left in them. Be careful, though, most of the ones I have ratted still have about 200v on the cap. Not lethal, but takes a nasty bite out of a screwdriver!!
Barry lennox
On 29 Jun 2006 15:54:45 -0700, fpga snipped-for-privacy@yahoo.com Gave us:
One name. RIFA.
Maxwell doesn't qualify due to your criteria. Find a RIFA distribution point, and buy some "sample quantities".
I have some experience with this, at the 10kJ level using 450V electrolytics in a 800V DC bus. they had 100k "balancing" resistors. which drew about 1/2 of the nominal leakage, anbd so did nothing. and even if they did, its only at DC; suck a wallop of current out, and watch the voltage distribute itself according to capacitance ratios. hardly surprising.
it got really interesting when we gassed the equipment with pressurised Methyl Bromide (Kids, dont do this, its a BAD thing). the +ve (IIRC; cant remember, cant be bothered working it out) cap terminal internal connection (very pure Al) corroded away very rapidly, leading to massive imbalances in the series-parallel stacks. At power-on the inrush "limiting" circuit limited peak inrush to 900A = peak rated current. This thump was big enough that the aforementioned cap value "balancing" occurred, over-voltaging the s*it out of some caps, which failed spectacularly (eg smashing a 1800V 300A SCR half-bridge physically to pieces). One 1,700A 400V drive did this whilst I stood beside it; the enclosure door nearly hit me, and I came close to s*****ng my pants.
In 5 18-hr days me and 4 guys replaced 2,000 capacitors in-situ. I personally hacksawed each one open. it was really interesting when we were working on the winch drives on the dredge, which got blown into the middle of the lake. 2m swells, and a tiny dinghy, with all the test gear on shore. The only way back was to power up the rebuilt drives, sans test gear, and cross our fingers. After ensuring the plant supervisor would take the rap ($$$) if any failed, which they didnt.
It was funny in that I was on the bridge, and noticed we were moving. I mentioned this, and was told we were not. To which I replied "OK, we arent, but the shore is." That got their attention. The wind was so strong it pulled the D9 bulldozer that was used as a mobile anchor into the 30m deep "lake". It was the 3rd one they had lost....
Cheers Terry
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