I've been setting back and watching this and hope some aren't confusing rms and
average voltage as the same thing. RMS or (root mean square) is calculated as
0.707 X peak voltage. The average voltage is calculated by 0.637 X peak
voltage. This is the way I was taught and is in several of my books here which
I already have double checked myself. There is only one power formula for
wattage (really two, one for DC and one for AC) but boils down to the same
thing. One can be fooled but rms and average are not the same. This can be
confused when talking about meter movements and them being designed to read
avarage or rms values (some average reading calibrated to read rms).
Quoted from the "Modern Dictionary of Electronics";
"Average power output of an AM transmitter: The RF power delivered to the
transmitter output terminals, averaged over a modulation cycle".
"Average value: The value obtained by dividing the sum of a number of
quantities by the number of quantities. The average value of a sine wave is
0.637 times the peak value".
"Average voltage: The sum of the instantaneous voltages in a half cycle
waveshape, divided by the number of instantaneous voltages. In a sine wave, the
average voltage is equal to 0.637 times the peak voltage"
The ac rms value is known as the "effective value" or the same value that would
produce the same work as a DC value.;
"Rms voltage: The effective value of a varying or alternating voltage. That
value which would produce the same power loss as if a continuous voltage were
applied to a pure resistance. In sine wave voltages, the rms voltage is equal
to 0.707 times the peak voltage".
"Watt: A unit of the electric power required to do work at the rate of 1 joule
per second. It is the power expended when 1 ampere of direct current flows
through a resistance of 1 ohm. In an alternating current circuit, the true
power in watts is effective volt amperes multiplied by the circuit power
factor".
The above explains the use of two wattage formulas. Notice it says the watts in
an ac circuit are the "effective" volt amperes which means the rms value, not
average.
Hope this helps reveal things through all the smoke.
Will
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