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.
Ouch. I have been schooled indeed, and of course I know 1/2 CV^2 and
should have been able to figure this out myself. Lazy boy.
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.
I have never seen a NiCd last that long. One is lucky to get a hundred
power cycles out of them. NiMH aren't even doing too well in my copious
supply of rechargable batteries at home. And of course a car battery
that makes it to seven or eight years is more the exception than the
rule.
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.
I'd just like to get more than 1-2 years. Laptop batteries too. At
three years there is a notable drop in charge time, no matter what you
spent on them originally.
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]
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