[CentOS] OT: watt-amps (was: wich apc ups?)

Tue May 29 19:12:39 UTC 2007
Steve Friedman <steve at adsi-m4.com>

On Tue, 29 May 2007, Mark Hull-Richter wrote:

> On 5/29/07, Jim Perrin <jperrin at gmail.com> wrote:
>> Watts =  Volts x Amps. I usually use a sliding scale based on # of 
>> machines.
> That has to be the stupidest marketing strategy ever devised.  Most
> people (yeah, me too) know that, but why can't they SAY so instead of
> using "VA"?...

This formula is correct for a resistive load; however, it completely 
ignores the reactive load.  The correct formula is:

   watts = power_factor X volts X amps

You consume volt-amps, but can only use for amps.  There are various 
regulations in place regarding the minimum power factor -- decent power 
supplies have a power factor of better than 90%.

Steve Friedman