On Thu, 07 Oct 2004 09:04:08 -0700, Bill Turner
wrote:

On Thu, 07 Oct 2004 01:28:13 -0700, Roy Lewallen wrote:

You can use the basic definition of RMS to calculate an RMS value of
power from the instantaneous power, but it's not useful for anything. A
resistor dissipating 10 watts of average power gets exactly as hot if
that average power is supplied by DC, a sine wave, or any other
waveform. That's not true of the RMS power -- different waveforms
producing the same average power and causing the same amount of heat
will produce different RMS powers. So average power is a very useful
value, while RMS power is not.

_________________________________________________ ________

That goes against everything I've ever read about RMS power, at least
for sine waves. I have always heard that a certain value of RMS power
produces the same heating as the same value of DC power. In your
statement above, you say that's true only for average power, not RMS,
and is true for *any* waveform, including sine waves.

Is there a new world order?

Bill,

If you read carefully in any of the handbooks where they discuss the
resistor heating by AC compared to DC you will see that they say "RMS
VOLTAGE that causes the same amount of heating in a resistor as the
same amount of DC voltage". They do not say the same amount of RMS
power.

Since a constant DC voltage would equate to average power in a
resistor, then if the same amount of AC RMS voltage causes the same
amount of heat it has to also be average power that it produces.

73
Gary K4FMX