On Sun, 11 Sep 2005 03:58:33 -0700, trader4 wrote:

"With AC, it's the sum of instantaneous products of current and voltage

over a cycle, divided by the product of their average values.
It's 1.0 if current is proportional to voltage. "

David's memory is correct. For AC, its the cosine of the phase angle
between the voltage and current. When there is zero phase shift, the
power factor is 1.0

As Nick Pine eludes to, this isn't a good definition because it doesn't
take into account the harmonic content of the waveforms. It works for
purely sinusoidal voltage abd current though. Power factor is more
appropriately the Power divided by RMS Volts * RMS Amps, or PF == P/VA.
The power can always be found by averaging the instantaneous V*A over the
cycle, as nicksanspam wrote above.

--
Keith