Jim Lux wrote: > At 07:31 AM 7/13/2007, Robert G. Brown wrote: > > >> For small/personal clusters I change my mind again. I tend to buy cheap >> UPS's for my house because our power bobbles for 1-5 seconds nearly >> every heavy rain/windstorm we have, which is why I know from direct >> experience that the batteries in these UPSs are lucky to last two whole >> years. I've got something like three of them where I'm plugged into the >> surge side because the UPS side is dead (no power at all) or goes down >> anyway when power bobbles, to the tune of system crash AND the maddening >> beeping. I'd love to find a 10 second PDU/conditioner that used a >> really large capacitor instead of a battery to buffer short outages,
Ten second non-chemical energy storage would be a good candidate for a flywheel. > > > Tough.. the energy density of lead acid is really high. > > Here's an example using one of those big 1 Farad 12V caps the auto sound > people use.. say the UPS can take voltage drop of 2V on the "battery". > At 12V it stores 72 Joules. At 10V, you've recovered 22J. That's about > 1/10th second, assuming the UPS is 100% efficient, which it isn't. > > > For 10 seconds, you need 100 Farad.. that's a BIG cap. > > > The battery life *should* be a whole lot longer (Lead Acid batteries can > have 10-20 year lives, as can NiCd), however, the run of the mill UPS > doesn't treat the battery very well. > > >> especially at mass market prices. > > That's the problem.. mass market means race to the bottom for quality > and life, to reduce initial price. You can get a PC UPS which provides > 10 minutes or so at 200-300VA for $50-70 at the local big box store. If > you were willing to pay, say, $300-400, you could probably get 20 year > life. > > (you could cobble one together cheaper.. a high quality charger is > probably $50-100, good quality battery is around $20, a high quality > inverter is $200 or so, and then you'd need some sort of transfer switch. > > > Take a look at products aimed at the sailboat/solar power market, which > are definitely aimed at longevity. > >> Does anybody know of such a beast? No battery, no toxins, just a big >> cap and small price? >> >> rgb >> >> -- >> Robert G. Brown http://www.phy.duke.edu/~rgb/ >> Duke University Dept. of Physics, Box 90305 >> Durham, N.C. 27708-0305 >> Phone: 1-919-660-2567 Fax: 919-660-2525 email:[EMAIL PROTECTED] >> >> >> _______________________________________________ >> Beowulf mailing list, Beowulf@beowulf.org >> To change your subscription (digest mode or unsubscribe) visit >> http://www.beowulf.org/mailman/listinfo/beowulf > > James Lux, P.E. > Spacecraft Radio Frequency Subsystems Group > Flight Communications Systems Section > Jet Propulsion Laboratory, Mail Stop 161-213 > 4800 Oak Grove Drive > Pasadena CA 91109 > tel: (818)354-2075 > fax: (818)393-6875 > > _______________________________________________ > Beowulf mailing list, Beowulf@beowulf.org > To change your subscription (digest mode or unsubscribe) visit > http://www.beowulf.org/mailman/listinfo/beowulf > _______________________________________________ Beowulf mailing list, Beowulf@beowulf.org To change your subscription (digest mode or unsubscribe) visit http://www.beowulf.org/mailman/listinfo/beowulf
