[Beowulf] UPS system for Linux cluster

Joe Landman landman at scalableinformatics.com
Thu Apr 30 14:35:05 EDT 2009


Lux, James P wrote:

> 
> Actually, this isn't particularly surprising to folks who deal with
> electrical power. It *is* surprising to folks who see volts*amps (VA)
> and think it means watts.
> 
> Most power conversion equipment has a higher VA rating than Watt
> rating (and, so do most loads, so it works out ok in practice)  PF
> (Power Factor) = Watts/VA, and a typical PF is around 0.85.

Most of the advice we've been given about "arbitrary" gear from power 
folks has been to use 0.7 (approximately 1/sqrt(2)) as your PF, to 
account for varying supply quality and leave an engineering margin (for 
error).  Indeed, looking at some of the PF curves for supplies under 
heavy load shows PF for "85%" supplies dipping into the mid to upper 70s.


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Joseph Landman, Ph.D
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