I just saw a TV commercial for PowerSave
I’m very sceptical. It sounds too good to be true. My other thought is that such a thing could be dangerous, especially if not installed by an electrician. I wouldn’t think a legitimate electrician would touch it.
So, my questions: Could it work? How? How dangerous?
(No, I’m not thinking of buying it, I’m just curious.)
The problem this claims to fix is actually a real problem, though they worded it badly. Motors can have a fair amount of extra current flowing through them out of phase with the voltage across them. Having this current circulate around the wires causes some resistive voltage drop along them, which generates waste heat.
In industry this is a big enough issue that they put capacitance across the lines. The current circulates as far back from the motor as the capacitor but no further, and there is less resistive loss.
In power transmission, it’s also an issue. So they put capacitors on utility poles, too - they’re the rectangular boxes with only two terminals on the top.
But in a house, this probably amounts to pennies a year, and wouldn’t be worth doing much to fix. So many of the things we use at home aren’t motors. This is only applicable to inductive loads, which pretty much means motors.
Google “power factor” or “VAR” to see more.
But the big draws of power in homes are usually motors, washing machines, a/c’s, refrigerators.
Residential power meters measure real power, not apparent power. A power factor (PF) correction device won’t affect the amount of real power you’re using. Even if your home has a crappy PF, and this product corrects it as advertised, installing it won’t save you a penny. In fact, it will actually cost you, since the device is not 100% efficient, and you’ll be paying for any heat it produces.
Of course, the power company would love it if you installed a PF correction device. While such a device will not save *you * any money, it will save the power company some money.
It smells like a scam to me; reason being it’s very light on controlled technical test data and very heavy on testimonials - that’s often the mark of a swindle.
Also, the consumer will have to pay to charge the cap up each time.
No free lunch and all that.
I think they’re claiming that the capacitor would be charged by power otherwise wasted - that’s the supposed basis of operation for this device.
It’s not a scam or anything esoteric, the device actually does what they’re claiming it to do. It’s just that residential users don’t really need it.
A power factor correction device isn’t a battery or other storage unit that puts more power into your system, rather, it works by altering the electrical characteristics of your home to be more favorable to power transmission.
AC power can be visualized as two sine waves - one for current and one for voltage. With no load, or a purely resistive load (most of the devices in your house), the waveforms will be “in phase”. The peak of the current waveform will occur at the same time as the peak of the voltage waveform. Their phase difference will be 0 degrees, and the power factor (the cosine of the phase difference) will be 1, indicating maximum power transmission.
Electric motors, as a side effect of their design, are inductive loads. Inductors, which are coils of wire designed to store energy in a magnetic field, do not allow the current to change instantaneously, because the magnetic field generated by the flowing current induces an opposing current in the inductor (self-inductance). That causes the current to “lag” the voltage. Think of the voltage waveform staying where it is, and the current waveform being “pulled” back - the peaks will no longer match up. In this situation, power is wasted.
The capacitor in the Power Save, or any other power factor correction unit, work to oppose the effects of the inductor. Capacitors, which are devices that store energy in an electric field, do not allow the voltage to change instantaneously. The voltage will “lag” the current. However, since the inductor has already caused the current to lag, the effect of the capacitor will be to “pull” the voltage waveform back in phase with the current waveform, decreasing the phase difference and increasing the power factor.
That’s my understanding of it, at least. If I’m being fuzzy somewhere, then, please help me out.
>A power factor (PF) correction device won’t affect the amount of real power you’re using.
Not so, Crafter_Man! Those big currents circulating between an underloaded induction motor and whatever acts as its big charge reservoir cause resistive heating in the supply wires. If the reservoir is close to the motor, those resistive losses only occur in the wires between them. If it is on the far side of your power meter, those resistive losses occur everywhere between the motor and the power meter and beyond. You aren’t getting more mechanical power out of the motor from these currents. But you are getting more real power in the form of heat delivered into your home. Multiplying the voltage by the current will far overestimate the watts delivered, because of the phase shift, and your meter doesn’t reflect that big overestimate. But the meter will include the electrical power that became heat in your wiring because of the circulating currents.
Yes, I realize that the device would help eliminate reactive power loss in the home wiring (and which you pay for). But the savings would be very small.
I don’t think so. Admittedly a/c’s do draw a lot in the summer (though I don’t have one), but heating devices (h/w heaters, electric stoves, clothes dryers and in my case, most of the home heating) are purely resistive. I think in my case, only the fridge is a significant resistive load.
If the heating losses in your home wiring were significant enough to cost you money, your wiring is probably not adequate, you’d be better off putting in some extra ways in your distribution board.
Power factor correction is virtually insignificant in your home, whilst there is an out- of-phase component, and this recirculating current will have a heating effect, you’ve got much bigger worries than power factor if this is a problem to you.
Hey, thanks guys. I appreciate that everyone brought the information to a level I could easily understand. I’ve done a little home electricial repair, and I was married to an electrician at one time so picked up a bit.
So, the consensus is that it may do what they say, but the savings they claim aren’t going to be there. So it’s kinda like an OTC drug that doesn’t do any harm, but doesn’t do any good either. pretty much what I expected.
So, would a reputable electrician tell a home owner not to bother? Or, would most just install it without comment, since the home owner already bought it?
Looks that way. If they had a product that made a consistent, measurable difference, they could just show the data, rather than supporting it with anecdotes of reduced bills that might be confounded by many other factors (and indeed might be a carefully filtered 0.1% of user responses - the other 99.9% being ‘it made no difference’ or ‘it costs more now’)
Possibly. Reputable electricians can still be wrong. I know plumbers who are otherwise quite reputable and intelligent, but swear by magnetic limescale reducers and fit them as standard when doing a central heating job.
This topic was included at school along with drawing power from the high tension lines running over your building. You could induce a current but it wouldn’t do you any good. Let’s not get into the legality of doing so.
True. And all of these, if the motor is large enough will already have a power factor capacitor. I know my AC unit does.
I brought this up 6 months ago in a thread about residential metering. If your meter measures (and charges for) KVA then power factor correction can help. If it measures KW then the savings would be very very small.
Small but not entirely insignificant although the 25% of your monthly bill savings claim is wildly exaggerated…
I have a 1 hp motor running my air conditioner. It actually draws 12 amps which is 5.5 amps more than that required for 1 hp in a 115 V circuit. If it is at the end of a 50 ft. #12 wire my excess i[sup]2[/sup]R loss is about 2.75 W. The thing runs about 16 hrs a day in the summer so that it costs me about 20 cents a month extra if electricity costs 15 cents/kWh.
I don’t think the device is worth the money. it would take maybe three years to pay for it at that rate if it costs $10. If you have to have an electrician install it, it certainly wouldn’t pay.
I suspect the capacitor on your air conditioner is a starting capacitor and not a power factor corrector.
Yes, it is. My bad.
I wouldn’t. I only know a little about power factor correction theory but I know enough to do research on a topic like this before a customer would pay me to do this type of work.
I’m surrounded by electrical engineers here at work, many of whom it is their job to deal with PF correction, so I wouldn’t have to go far to get an answer.