[CentOS] OT: watt-amps (was: wich apc ups?)
Steve Friedman
steve at adsi-m4.com
Tue May 29 19:12:39 UTC 2007
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
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