On (15 Jan 98) MIKE ROSS wrote to Tim Hutzler...
 MR> Power factor is the ratio of true power (P) to apparent power (S). With
 MR> DC your 100% value would be correct since in a certain sense P and S are
 MR> one and the same thing.
So far so good......
However there exists no such thing as an
 MR> apparent power in a DC circuit. Thus the notion of power factor with DC
 MR> is meaningless. There really is no PF in DC and is therefore not 100%.
To uphold my "talent" for nit- picking, I draw your attention to the brief
switch-on, and switch- off intervals in a DC circuit.
In these intervals, the circuit inductance or capacitance is sometimes more
influential than what the load resistance is. The energy in the magnetic
field, and the energy in the circuit capacitance will affect the "apparent
power". But, may not be measurable as real power as detected by voltmeter and
ammmeter at the load.
I used to work in a shop where truck magnetos were overhauled [1940s]. A 110v
DC electromagnet was used. When the supply was switched on, nothing much 
ould
happen but slowly, the amps would creep up to the full value. The delay, was
due to circuit inductance.
The magnet coil had a 240v carbon filament lamp permanenty wired in parallel. 
When
the supply switch was opened, that lamp [initially dull] would flare very
bright. Due to the release of magnetic energy from the big magnet. That 
nergy
flowing, even though there was NIL connection to the 110v mains at that time.
You might say that here is an analogy of "power factor". The apparent power
very high, the real power quite low.
In an AC circuit, it is the capacitance and the inductance that account for
the discrepancy between real power and apparent power. To "improve" power
factor it is common practice to connect capacitors across loads.
AC is simply DC, that wobbles. The same rules apply!
Cheers.........ALEC
... ******FLASH! Energiser bunny arrested, charged with battery******
--- PPoint 1.92
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