Power factor question

[Caveat]

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?

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

 

[PeterD]

On Thu, 27 Mar 2008 23:16:42 -0700, "Caveat" <caveat-lector@cox.net>
wrote:

...

My questions are . . .



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

Maybe not... It may be one of those things that just 'comes' to you
one night at 3 AM...

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

None that I know of...

 

[Charles]

"Caveat" <caveat-lector@cox.net> wrote in message
news:c30Hj.12448$6J3.8141@newsfe13.phx...

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.

 

[caveat]

Thank you both for your answers.

 

[w_tom]

On Mar 28, 10:01 pm, "caveat" <caveat-lec...@cox.net> wrote:

Thank you both for your answers.

Expanding on what Charles said. Idea is to get both current and
voltage to 'sine wave' simultaneously so that all power is useable.
Many ways of doing this. For example, one reason why both peaks don't
occur simultaneously and clean is other harmonic frequencies combined
with the 60 Hz frequency. That LC filter simply removes harmonic
frequencies.

Capacitor and coil will shift 60 Hz sine wavest back towards each
other (if properly designed).

Today, power supplies are required (not everywhere) to have dynamic
power factor correction. Some reasons for bad power factor are
devices that create an inductive load (motors and fluorescent bulbs)
or electronic devices that only take power from part of the wave.
Later devices have or will have dynamic power factor correction. A
circuit that some might confuse as a line filter.

Electric distribution systems also install power factor correction
on some telephone poles in their distribution. These cylinder devices
(smaller than transformers) are nothing more than capacitors to
compensate for neighborhood inductive loads from motors, et al.

Another trick too complex to explain here is to setup a synchronous
motor that simply runs with no load. That motors is setup to perform
like a varying capacitor so that factory power is power factor
corrected.

 

[cadman]

Power factor correction is not an issue for residential consumer.

This is seriously untrue these days with EMC.

Any device drawing current must do it in a steady way.
You cant use simple diodes and capacitors as this only takes current
at the peaks of the waveform.

This means you need either a SMPS or some front end filtering to
ensure the current flow is steady.

 

[PeterD]

On Mon, 31 Mar 2008 15:53:57 -0700 (PDT), cadman
<cresswellavenue@googlemail.com> wrote:

Power factor correction is not an issue for residential consumer.

This is seriously untrue these days with EMC.

Any device drawing current must do it in a steady way.
You cant use simple diodes and capacitors as this only takes current
at the peaks of the waveform.

This means you need either a SMPS or some front end filtering to
ensure the current flow is steady.

WTF? Oh, I get it, it is April 1! Ok...