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From: jeff@rtech.ARPA (Jeff Lichtman)
Newsgroups: net.consumers,net.analog
Subject: Re: power meters
Message-ID: <267@rtech.ARPA>
Date: Wed, 27-Mar-85 03:33:29 EST
Article-I.D.: rtech.267
Posted: Wed Mar 27 03:33:29 1985
Date-Received: Mon, 1-Apr-85 03:42:59 EST
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Organization: Relational Technology, Berkeley CA
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Xref: watmath net.consumers:2076 net.analog:245

> > ... AC power equals RMS voltage times
> > RMS current times the cosine of the phase angle between them.
> 
> This is strictly speaking true. However
> 
> 1) Most devices are designed to have a power factor close to one.  In
>    this case the power consumed does equal scalar voltage times scalar
>    current.  For example flourescent lamps have a capacitor solely for
>    power factor correction.

Motors running with a load on them can have power factors close to one,
but when the load decreases the power factor decreases and gets close to
zero.  For example, the power factor of a refrigerator motor is close to
one when the motor is starting, and much lower when it is running normally.

> 2) Domestic electricity meters measure scalar voltage times current and
>    the person in question was interested in optimizing for minimum
>    electricity bill and not particularly for minimum power.
> Paul Wilcox-Baker.

Domestic electricity meters *do* measure true energy.  They will even run
backwards if there is a net outflow of energy.  My father, who has
a graduate engineering degree, assures me that this is true.
-- 
Jeff Lichtman at rtech (Relational Technology, Inc.)
aka Swazoo Koolak