ot kinda:capaciters to save on bill

wippin' boy · Aug 23, 2009

so i kind-sorta understand the whole capacitance inductance thing with electricity.
i know that in the old days sometimes shops were required to put in capacitors to help with the inductance load from all the motors
anyway
a buddy asked me if the capacitance machines they sell on the internet can really save you a bunch of money balancing your motor loads
my gut feeling is if there was any thing to it I'd have something in my shop cause i run $7,500 a month electrical bill. A huge percentage of which is motor loads
well
just another scam or what?

peterh5322 · Aug 23, 2009

Power factor correction is a real-deal option for those who are on a commercial meter, which gets changed for not only the peak load during a billing cycle, or a rolling group of billing cycles, but also for real plus apparent power, not just for real power as is traditional for non-commercial meter.

It is perhaps more effective to apply power factor correction on a per-machine basis, as otherwise it is indeed possible to over-correct.

To be compliant with the NEC, the PFC caps would have to be placed on the load side of each motor controller, but before the motor overloads.

rons · Aug 23, 2009

It is not a scam. But it is a disadvantage if you are not wisely using PFC.
An example. I checked into PFC for a Miller Synchrowave 350.
With no PFC:

Full rated output = 110 amperes
Idle = 2 amperes

With PFC:

Full rated output = 78 amperes
Idle = 69 amperes

If the machine is not idling most of the time then PFC is an advantage.
Otherwise electricity is wasted.

wippin' boy · Aug 24, 2009

so now that we know what to call it
the question becomes
is power factor correction applicable in a home setting
figuring 1 well pump,a washer and dryer and a shop compressor?
and from your description peter it sounds like a "magic pfc machine" would have to be NEC improper because the guy was talking about a self contained device he would hook up to his panel

JST · Aug 24, 2009

basically "not yet'.

Unless you are billed for your power factor, which residences are not yet, all it will do is cost you money, not save it.

The standard residential meter is actually adjusted to not even respond to power factor/reactive power. So there is no way to bill for it.

With the new 'smart grid" stuff, I believe the meters will be able to measure everything, and even (with added equipment) shut off things that you "shouldn't be using now". So then as soon as the tariffs for your state allow it, the power company could bill you for power factor. but I don't know of anywhere that is done for residential service now.

if you have a lot of CF lights, which you replaced incandescents with, your PF will be headed down (which is bad). CFs have a low power factor.

wippin' boy · Aug 25, 2009

thanks.....

Dave K2 · Aug 25, 2009

We have PFC at work, mostly printing machines etc, its got a bank of caps, contactors and a controller. The power it uses is surprising at around 100A / 415v but our bills (max demand billing) went down and our measured power factor is generally around 1.00 - 0.99 which is pretty damn good.

I have also asked about the home workshop but was told the same answers, the poor power factor punishes the supply company/grid etc but the meters cant detect it so its free, just a waste though. It does cause cable heating though.

Its an interesting topic.

Dave

JST · Aug 25, 2009

Dave K2 said:
We have PFC at work, mostly printing machines etc, its got a bank of caps, contactors and a controller. The power it uses is surprising at around 100A / 415v but our bills (max demand billing) went down and our measured power factor is generally around 1.00 - 0.99 which is pretty damn good.

Actually, most of the indicated current is NOT power... it is VARs.... "volt-amperes reactive", aka "apparent power.

In fact capacitors MAKE "poor power factor" just as motors and other inductors do. The key element is that they are the exact OPPOSITE of inductors, so the correct size capacitor cancels out the inductive effect.

You want to be careful. The capacitors and inductors form a resonant circuit. if the PF is really 1, they are resonant 'dead on" 60 Hz, and the voltage may be way too high, depending on loads.

Correcting to 0.9 or so should be way good enough. The power companies generally require that any other power generating facilities (wind etc) must generate power while accepting a PF of 0.8, so that they take their fair share of the VARs.

Generally, adding capacitors will raise voltage as well as correct the PF, until you go past resonance and end up with poor power factor on the capacitive end.

NewTown · Aug 26, 2009

Although this comment isn't in regards to capacitors or power factor, I think it does apply to the topic.

It is my understanding that residential meters read the highest KW on whichever leg is the highest. Since there are 2 hot legs that come in to a main breaker, would it be beneficial to split the house wiring so that each leg is being used about the same? By running a shop compressor on one leg and the water pump on the other, would the meter only read whichever is pulling the most current?

peterh5322 · Aug 26, 2009

"By running a shop compressor on one leg and the water pump on the other, would the meter only read whichever is pulling the most current?"

But, in North America, all such loads are usually 240 volts, so these implicitly use both legs.

I have recently encountered several premises which have had 120/240 volt service drops, but only one line and the (grounded) neutral which go into the weather head, and thereafter to the meter. (The other line was terminated in an insulator, and was not used).

Yet, these same premises had 125 amp 120/240 panelboards, and the two buses were wired in parallel, fed by the single 120 volt service.

Real head-scratchers, those.

jim rozen · Aug 26, 2009

"It is my understanding that residential meters read the highest KW on whichever leg is the highest."

This is incorrect, at least for all the residential watthour meters I've ever seen.
If you ballance your 120 volt loads perfectly, the neutral has zero current and
it is though the entire house is running on 240. But if you start out with
20 amps in one incoming hot, and then change to 10 on each, you will pay the
same.

Here in peekskill there was at least one house that only had 60 amp, 120 volt
service running into it. I know because I almost bought the place, and later
my wife did the closing on it. Their bank would not write a loan on the place,
based on the service they had. So they had to get it upgraded to a modern
version.

It was a small two bedroom house, oil heat, natural gas hot water and stove.
The electric service was really only for lighting.

Jim

wippin' boy · Aug 27, 2009

Here in peekskill there was at least one house that only had 60 amp, 120 volt
service running into it

ran into the same once
guy had the inside gutted to remodel
whole place was made out of used packing crates from the rail road

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