[Beowulf] power usage, Intel 5160 vs. AMD 2216

Robert G. Brown rgb at phy.duke.edu
Fri Jul 13 14:28:11 PDT 2007

> 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

>> 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.


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:rgb at phy.duke.edu

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