A device that claims to save electricity when plugged into the mains - how does it work?

April 18, 2007 7:25 AM

This product claims to save electricity through some sort of voltage and current regulation. This raises my suspicions, but there might be some explanation for it I've missed, probably down to some peculiarity of mains electricity?
posted by edd to science & nature (17 comments total)

I should have looked here first, which is setting off alarm bells.
posted by edd at 7:29 AM on April 18, 2007

From the FAQ:
Q17: I have a wireless energy monitoring system and when I plug in my Power Saver, the system shows that my Power saver is consuming some energy? Why?

Ans: We are aware of some compatibility issues between the Power Saver and some of the energy monitoring systems that are available in the market. The monitoring system is designed to give instantaneous reading of the current that it sees flowing through the terminal of any device and therefore can not distinguish between the energy that is being consumed and the energy that is being stored for later use. The power saver has to store some energy in order to act as a voltage stabilizer and therefore it is not actually wasting any energy.



Q18: I have a small plug-in gadget that shows the energy consumed by an appliance plugged into it. When I plug in my Power Saver into such a gadget, it indicates that the Power Saver is consuming energy? Why?

Ans: Please see Q17. In addition, the high frequency sampling circuitry used in such gadgets is designed to take an instantaneous reading and this can affect the frequency response of filter inside the power saver thus making such gadgets give erroneous readings. Therefore it is recommended that Power Saver should be plugged directly into a wall socket and not into any other device or gadget.


That's too funny. It not only doesn't save energy, it uses it.
posted by caddis at 7:39 AM on April 18, 2007

There is actually a way you can 'steal' power from the power company by doing something with the 240v/120v lines. I'm not sure about the details, but it's possible to do. You do it at the point where your house gets power, though.

This thing seems to be a scam, though.
posted by delmoi at 8:06 AM on April 18, 2007

delmoi: Interesting. Note that it's a UK product here by the way, so we don't have 120V to monkey with!
posted by edd at 8:10 AM on April 18, 2007

They also sell a fuel saver (your second link):
Ans. The EPS Fuel Saver is a fuel economiser and pollution reduction device, which utilises magnetic hydrodynamic technology to improve the combustion of hydrocarbon fuels. It can be easily installed in minutes by strapping it onto the fuel line next to but just before the fuel pump, the injection fuel rail, or the diesel pump.

**WARNING! THIS IS BULLSHIT.**

Magnetic hydrodynamic technology?
Oh, and cumbustion isn't what's really hurting your efficiency. (Cumbustion is actually quite good in a gasoline engine, I don't have the numbers here right now, but I'm sure another poster does).
The laws of thermodynamics are a big problem. (See http://en.wikipedia.org/wiki/Carnot_heat_engine )

Clear 'nuff? IAAME (Mechanical Engineer)

As to the electrical one.... well, once a sucker, maybe you can get 'em twice... that's my take on it.
posted by defcom1 at 8:13 AM on April 18, 2007

delmoi, are you thinking about inductive versus reactive loads?

Household power meters read one type, but not the other. If you have a lot of inductive devices, like motors, these don't get measured correctly. This is why large factories have banks of capacitors to offset it. I'm not doing a very good job explaining it... one of MeFi's resident electrical techs will do a better job.
posted by odinsdream at 8:21 AM on April 18, 2007

The description of how the device works is gibberish. It's most likely that it does absolutely nothing. There's a slight chance that it does some amount of power factor correction on a reactive load, but even if it did it still wouldn't "reduce your electricity bill and save you money".

Verdict: Crap.

Disclaimer: I have an EE degree but expertise is not in power transmission.
posted by kc8nod at 8:21 AM on April 18, 2007

Ah, more information about efficiency (and where the energy goes) here:
http://en.wikipedia.org/wiki/Internal_combustion_engine#Engine_Efficiency
Somehow energy "filtration" etc. just sounds like marketing garbage to sell you crap.
posted by defcom1 at 8:23 AM on April 18, 2007

The "Fuel Saver" one looks familiar. I think that exact product might have been shown on a Mythbusters episode where they tried this and a few other of these types of devices (none of which worked).
posted by joquarky at 8:27 AM on April 18, 2007

Paging asavage...
posted by grateful at 8:34 AM on April 18, 2007

A friend of mine who was head of the conservation department of a major city utility (a lawyer, not an EE) told me that residential customers are not charged for inductive loads in the US, typically, but commercial customers are. (I recall her contrasting inductive and resistive loads though, not reactive.) I don't know how things are in the UK. It's conceivable a device could reduce the big inductive loads at motor start-ups by stuttering the power or something, but I'd have to be sure that any such device didn't have any potential for overheating the windings in the motor.
posted by jamjam at 8:55 AM on April 18, 2007

defcom1: That was my opinion exactly. I just didn't express it in quite the same way!

I would be prepared to accept there might be a sufficient gap in my knowledge of household electricity supplies, but the same does not apply to that fuel thing. As I hinted, if I'd seen that one first I'd never have bothered asking the question.
posted by edd at 9:03 AM on April 18, 2007

I believe the term you're looking for, odinsdream and jamjam, is power factor. Apparently some power companies will penalize you severely if your power factor gets too far off. That's why large customers with bad power factors install equipment to fix it.
posted by wierdo at 10:58 AM on April 18, 2007

Oh, and of course I forgot the rest of my post, which was to say that the product is a bunch of crap. If you lower the voltage, all you gain is increasing the current, and vice versa. You draw the same wattage either way, only with loss from the transformer eating up more energy.

Many higher-end UPSes have what they term a "constant voltage transformer," or in the case of APC, automatic voltage regulation, which prevents the UPS from switching to battery due to a slightly low line voltage. In the US, they generally work from 98-130v, and switch to battery if the voltage is outside that range. In the case of a UPS, it does save a little bit of energy, since the UPS isn't wasting any electricity to charge or drain the battery as often, neither of which is 100% efficient, both due to losses in the battery and the step-up and step-down transformers to change line voltage to battery voltage and battery voltage to output voltage, but that's by bypassing loss, not by some magical property of a transformer.

As with anything else, you don't get something for nothing. When line voltage is low, you draw more current than normal, and when it's high, you draw less current.
posted by wierdo at 11:07 AM on April 18, 2007

Delmoi, you may be referring to power factor correction. Power consists of two components, the real power and the reactive power. The real power is what is actually consumed in your home, which your power meter measures and you are charged for. The ratio of real power to total power is the power factor. For a light bulb the power factor is 100%. All of the power going to the bulb is real and consumed in your home.

Reactive power is used in devices like electric motors and computer power supplies that contain inductors. For these devices the power factor may be only 65% to 85%. So you are only using 65% to 85% of the power actually delivered to your home. Reactive power is stored in the device for one half cycle and returned to the power company in the second half cycle. It is not really consumed in your home, just borrowed for a few milliseconds at a time. So it is not measured by the power meter and you are not charged for it.

So if you are not actually using the reactive power, why would the power company care? It is because there is some actual loss of real power in shipping the reactive power back and forth to your home. Primarily this is heat loss in the transmission lines, just like a toaster.

You can think of reactive power as like buying an item from Amazon but changing your mind and returning it for a refund. No net money changes hands, but there are shipping costs and in the power company's case they pay the shipping both ways. There is also the fact that handling the reactive power requires the power company to have a bigger power plant and bigger transformers to handle the power traffic even though not all of it is used or metered. For Amazon it would be like paying to stock a larger inventory of items to handle the percentage of items that uselessly travel back and forth to non-paying customers that return items.

Since reactive power results in real losses, there are environmental and economic reasons for requiring power factor correction in inductive devices. For computer power supplies, it requires some extra circuitry to adjust the way the supply draws power. For large factories with lots of high power motors, the power company charges a lower rate if the company puts in a large bank of capacitors next to their power transformer to correct their power factor. You can think of the motor as borrowing and returning reactive power from the local bank of capacitors each cycle instead of over the transmission lines to and from the power plant.

So getting to the original question, does this device perform power factor correction? Doubtful, but even if it did, it would not save anything on your power bill because the meter doesn't measure reative power and you aren't charged for it anyway.
posted by JackFlash at 11:23 AM on April 18, 2007

odinsdream and jamjam:

The distinction is between resistive loads and reactive loads, where the latter can be either inductive or capacitive.
posted by springload at 4:49 PM on April 18, 2007

Thanks for the clear explanation, JackFlash. It's a lot better than the explanation my professor gave us.
posted by odinsdream at 6:35 PM on April 20, 2007