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Archiver > TMG > 2003-06 > 1054882314

From: "Cheri Casper" <>
Subject: RE: [TMG] Comment on UPS
Date: Thu, 5 Jun 2003 23:52:13 -0700
In-Reply-To: <>

Looks like we need a new patch so there will be some new threads for
discussion. Looks like we are getting desperate for subject matter. <g>

-----Original Message-----
From: Richard Brogger [mailto:]
Sent: Thursday, June 05, 2003 11:17 PM
Subject: Re: [TMG] Comment on UPS

Dennis Lee Bieber wrote:
> UPS units are rated in Volt-Amps (I've never been quite clear on
> how that differs from plain old wattage).

You may not want to know. <g>

In a DC circuit Volts * Amps (VA) does equal watts. In an AC circuit,
Volts * Amps * Power factor equals watts. With a purely resistive
circuit the power factor is one (unity) and thus V*A still = Watts.

However, most loads are not purely resistive. Capacitance and
inductance will cause the voltage and current to be out of phase and
one is, so to speak, not pulling at the same angle as the other. When
volt and current are out of phase, they will not produce as much power
(watts) as when they are in phase.

Capacitance will produce a leading power factor while any load that
involves windings, such as a motor or transformer, will produce a
lagging power factor. All loads combined tend to average out to about
a 0.8 lagging power factor. If, for an AC circuit, you were to say
Volts * Amps * 0.8 = Watts, you will probably be closer to the correct

That is a rough explanation but I hope that it will help.

Richard Brogger

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