"Caveat" wrote in message
...
Hi all,



I have a question about the term "power factor".



A number of years ago I was an install tech. for a company that sold
Nortel phone systems. I noticed that almost all the small units were sold
with a plug-in device that weighed about 25 pounds and I first thought it
was a very heavy-duty filter/surge suppressor but I was amazed to find out
that such a large unit was only rated for 6 amps. When I opened one up I
found it to have only two components, a HUGE doughnut coil (that made up
about 4/5th. the weight) and a HUGE capacitor, it was simply an L-C
circuit.

I asked one of the tech's what it was and he told me it was a power factor
device.



I ended up with two "spare" units and used one for my A/V system and the
other for my computer network. After finding out that nothing had changed
with either application I gave them away to a, at the time, friend of mine
who designs and tests battery backup and power supply units for ships and
private jets - thinking he might find a use for them.



Tonight I was in another NG and read a post about surge suppressors and
they were talking about power factor correction and that reminded me about
this so I looked at wikipedia for an explanation of power factor. What I
got was a little over my level of understanding.



I know a little about electronics, I did TV repair in the late 1980's but
didn't get too far into the theory of electronics so I would say that my
understanding is about at a 1st to 2nd semester level of electronics
understanding.



Sorry for the long winded intro.



My questions are . . .



1. is there an easy way to understand power factor and power factor
correction?

Sure. When the voltage and current are 90 degrees out of phase, the energy
transfer is 0 because the power factor is 0. What is happening in this case
is that the load is storing the energy and then returning it to the source.
That is the extreme case and seldom happens in reality. When the voltage
and current are in phase, the power factor is 1 and VA = watts ... often
happens in reality with resistive loads. Motors (inductive loads) and
switch-mode power supplies (capacitive loads) have power factors between 0
and 1. This means that volts times amps do not equal real power. The
cosine of the phase shift between current and voltage (on the input side) is
the power factor. Power factor correction is the use of capacitors with
inductive loads to shift the phase back towards 0. Often used when lots of
motors are on line.

2. is there any reason a person would want one of these units for home
use?

Power factor correction is not an issue for residential consumer, but can be
a big issue for commercial/industrial consumers. The energy supplier will
often penalize a commercial user for a bad power factor (charge a higher
rate based on kWh). The user can save money by using correction capacitors
or power supplies designed to increase the power factor.