Re: HMC Question - UPS issues

[Larry Bolhuis <lbolhuis@xxxxxxxxxx>]

It certainly applies to both that's for sure.  What I seem to recall is 
that the reason that VA is not the same as Watts exactly is because of 
the sine wave nature of AC current.  The available power is only the 
area under the curve. The voltage we normally speak about is RMS (root 
mean square) voltage not peak voltage. RMS gives a pretty decent 
approximation of the power that would be available if we had square wave 
power at the stated voltage (as some older UPSs used to generate when on 
batteries)   The peak voltage of an AC circuit is higher than RMS 
voltage and I believe the differnce is that between VA and Watts.

- Larry

ps: If the Ohm is the unit of measure of resistance, what is the unit of 
measure of conductance?

daparnin@xxxxxxxxxxxxxxxxxx wrote:

> This goes back a few years, but isn't Ohm's Law only applicicable to DC,
> not AC.  Hence, they came up with volt-amps as a means of expressing the
> power requirements.  I sat through an American Power seminar 10 or 12 years
> ago where they explain what it was all about.  Unfortunately, you use it or
> loose it.  ...and I'm loosing it (along with some of my hair).
>
> Dave Parnin
> Nishikawa Standard Company
> Topeka, IN  46571
> daparnin@xxxxxxxxxxxxxxxxxx
>
>
>
>
> UPS' have ratings of vA (volt-amps). These seem similar to watts - remember
> PIE (Ohm's Law)? P = I x E (P = power in watts, I = current in amps, E =
> voltage in volts). It may not be completely accurate, but I find the load
> for each unit attached to the UPS - it's usually on a label in back. Add'm
> up. You probably want to worry about peak vs. average. I'm sure others have
> more info, and the manuals (perish the thought of RTFM) have guidelines for
> all this.
>  
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