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Re: [Amps] rms Volts, Amps and Watts

To: <amps@contesting.com>
Subject: Re: [Amps] rms Volts, Amps and Watts
From: "Paul Christensen" <w9ac@arrl.net>
Date: Sat, 9 Mar 2013 17:37:31 -0500
List-post: <amps@contesting.com">mailto:amps@contesting.com>
rms voltage x rms current does not give rms power. It gives mean or average power. rms power can be calculated but has no useful value.

An insightful perspective on "RMS Power" can be found here:

http://www.eznec.com/Amateur/RMS_Power.pdf

As Steve notes, it's a meaningless term that through the years, became an abused adjunct for the multiplication of RMS voltage and RMS current. In 1974, the U.S. Federal Trade Commission required manufacturers of stereo audio amplifiers to state power in terms of "continuous watts." Even so, only a few did after the new regulation went into effect.

Most of us probably remember some of the absurd power claims made mostly by importers of Asian stereo equipment. Back in the early '70s, our own household had a "200-watt" stereo system that if measured today probably could not produce 5 clean watts of power per channel.

Between 1974 and now, a lot has changed with the advent of multi-channel sound systems designed for home entertainment. For those interested, the most recent regulatory update occurred back in 2010 and can be found in the link below.

http://www.ftc.gov/os/2010/01/P974222amplifierrule.pdf

Paul, W9AC
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