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Passive Power Factor correction

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Posted by Martin Riddle on October 9, 2008, 11:06 pm
Has anyone have experience with something like this?


Posted by Cydrome Leader on October 10, 2008, 5:53 am

In short, it's a scam.

there is some truth behind power factor correction saving power, but it's
not 10 to the totaly bogus 25% savings they claim.

Posted by Eeyore on October 10, 2008, 6:49 am

Cydrome Leader wrote:

In industrial situations.

But it doesn't affect the home consumer whose meters read only TRUE power and
PF won't affect that.


Posted by Eeyore on October 10, 2008, 6:45 am

Martin Riddle wrote:

Load of old garbage. Individual consumers don't need power factor
correction as the power company doesn't bother charging it for them.

They should be prosecuted for FRAUD. Refer it to you local DA


Posted by Neon John on October 10, 2008, 2:16 pm

That old fraud again.

In a very simplified nutshell, a load with a power factor less than 1 draws
both real power and "wattless" or reactive power.  "wattless power" seems like
a contradiction but its the slang used in the power industry.  Wattless amps
flow out of phase with the voltage waveform and are caused (usually) by loads
that have an inductive component (electric motors, primarily) or (rarely) by
loads with capacitive components (un-PF corrected switchmode power supplies,
some types of fluorescent lights, etc.)  The real amps and the wattless amps
add quadratically to produce the total amps.

Here's the critical part.  Revenue meters only measure REAL power (some of the
new electronic ones also measure VARs [reactive power] but do not bill for it)
and REAL power is what you're paying for.  Large commercial customers can be
billed for low PF (excessive VARs) but never in a residential or small
commercial (200 amp) service.  Reactive power simply flows through the lines

Most VARs are lagging - that is, the current lags the voltage by some phase
angle.  What that box does is supply leading VARS to counteract the lagging
VARS.  That reduces the amps flowing through the circuit upstream of the box
(which is what they show unsophisticated customers) but that reduction has
essentially NO effect on the REAL power metered by the revenue meter.

I say "almost" because the extra amps flowing through the wire's low but
finite resistance developers a little heat.  This is real power and gets
metered.  The amount is tiny, though, a few watts at most.

The box contains ordinary motor run capacitors.  Problem is, these capacitors
are not perfect - none are - and so they dissipate a little heat themselves.
That again is REAL power that is metered and billed for.  Again, it is a small
amount but it may very well exceed the amount of power saved by reducing the
current in the low power factor house wiring.

Worse, the box supplies a fixed amount of leading VARs.  When those VARs
aren't needed by, say, a furnace fan motor, they flow back out the service
entrance and to the utility network.  The current flow through the conductors
between the box and the meter causes another small voltage drop and therefore
some heat generation.  The amount of REAL energy consumed is undoubtedly small
but it very well could exceed any "savings" caused by correcting low PF loads
in the house.

In other words, having this very expensive box in place could and probably
will cost you a few cents more a month on your power bill.  I bet they charge
a kilobuck or more for this box so that's money just pissed away.

There is only one instance where PF correction makes sense for small
consumers.  That is, when the wattless current is (on the verge of)
overloading the service entrance.  Even then, this box is the WRONG way to go
about fixing the problem.

Let's suppose you have a store with lots of low PF pre-energy efficient
fluorescent lights inside and lots of neon signage outside.  Low PF
fluorescent fixtures typically have a PF of around 0.5.  Low PF neon
transformers around 0.4.  That means that the fluorescent lamps draw TWICE the
current necessary to provide the fixture's wattage.  The neon draws a little
OVER TWICE the necessary current.

If lighting and signage makes up the bulk of your load and the total current
is near or exceeds 200 amps then you'd be experiencing tripped main breakers,
an overheating breaker panel and perhaps complaints from the utility.

The thing is, only half that 200 amp (assuming an average pf of 0.5 at the
service entrance) is necessary to operate the lights and signs.  The rest is
lagging reactive amps that do nothing other than heat wires and trip breakers.

If someone like me comes in and corrects each low PF load by placing the
appropriate capacitor across the load's power terminals so that the overall PF
is now 1, only 100 amps is drawn from the utility.  The other 100 amps are
supplied by the capacitors that are scattered around the facility.  I normally
correct each neon transformer at its power terminals and each fluorescent lamp
string (not worth the cost to do each lamp individually).

This process saves very little money on the power bill but it DOES eliminate
the excess current draw, the overheating, the complaining from the power
company and it opens up those 100 amps for other loads in case the store

I would NOT use a box like that company is peddling.  I use motor run
capacitors which, bought wholesale, cost about $ ea.  Here's a photo of one


I repeat, this procedure is NOT necessary and is NOT financially justified
unless the service entrance and panel is being overloaded by low PF VARs OR
your power company is threatening a low PF penalty charge.  The latter is very
very rare on 200 amp services.

Here's another situation.  Suppose a business has a sign out on the street,
located several hundred feet from the breaker panel.  The sign is mostly neon.
It has a 30 amp branch circuit run to it through either underground conduit or
direct-burial cable.  The sign is pretty much fully loading the branch,
drawing a little less than 30 amps.  Since the neon transformers have low PF
(around 0.4), over half that current is wattless.

Now suppose the store operator wants to install a larger sign with more neon.
The 30 amp branch is at capacity and running a larger one would require
tearing up his parking lot, costing thousands of $$$ and leaving an ugly scar
on his pavement.  What to do?

We go into the sign and PF-correct each neon transformer (or buy high PF
transformers that have the caps built in) in the new sign.  With each
transformer having a PF near 1, we can draw twice the real power over the same
30 amp branch.  IOW, the sign can be twice as large while drawing the same

The sign will, of course, cost twice as much to operate so the cost savings is
strictly in not having to dig up his pavement and run a larger branch.
Presumably the larger sign will draw more customers and thus pay for the extra
power consumption.

Making neon signs myself, I've run into this situation MANY times.  Few sign
shop operators understand the concept of PF so I've been able to "save the
day" a number of times for sign shops that bought wholesale neon from me.

The only other common situation where correcting a low PF load makes sense is
when you're trying to run the load from a generator that is being overloaded
by the wattless current.  We touched on that yesterday in another thread.  In
this instance, correcting the PF of the low PF furnace blower will allow the
generator to handle the load AND power some other loads.  It will also save
fuel so if you're off-grid or experience frequent power outages, PF correction
might be worthwhile, depending on your existing PF and how often you run your

Pre-energy-efficient fluorescent lamps, some mercury vapor and HID lamps and
lightly loaded motors (typically HVAC blower motors) are typically the only
low PF loads in the house.  Some microwave ovens are also low PF.  Most
fully-loaded motors have high PFs.  Typical is the measurement someone posted
recently of his refrigerator having a 0.95 PF.  If you have one, a well pump
may or may not be low PF, depending on how it is sized.  A deep well pump in a
shallow well is quite under-loaded and will have a low PF.  The only way to
know is to measure.  

Let me repeat again, unless you're running out of service entrance capacity or
are having to run the load using a generator, low PF simply doesn't matter
around the house or small business.

If there is a lot of interest in this then I'll do a web page on DIY PF
correction.  However, unless you have a special circumstance such as those
listed above, it's simply not worth the effort.  It would take years for the
tiny power savings to pay back the cost of even $00 worth of capacitors.

John De Armond
See my website for my current email address
http://www.johndearmond.com  <-- best little blog on the net!
Tellico Plains, Occupied TN
You can't turn [MS] shovelware into reliable software by patching it a whole
lot. -Marcus Ranum

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