'Power Saver' ?!

[I_Need_Solar]

http://www.energyenv.co.uk/PowerSaver.asp

Has anyone bought/used one of these, or any idea how/if this works?  It sounds too good to be true...

They are also available (cheaper) on eBay.

Matthew

[Ivan]

Sounds too good to be true to me. Certainly some products have poor power factor (but I think that can decrease apparent energy useage), I think also, modern standards probably discourage poor power factor products.

Ivan

[spongebobgreenpants]

can anyone explain 'power factor' in layman's terms?

sb
cheers.

[Ivan]

I can do that quite easily, but don't ask me to explain it in technical terms- that's a bit harder.

Power factor is a measure of how 'in phase' the voltage and the current are in ac systems. For example, with resistive loads eg a heater, it should be perfect. However, if you have wire-wound devices or capacitors, the current/voltage relationship shifts. Wound components tend to resist changes in current - so although the voltage may rise, the current lags behind (caused by back emf ie 'induction'). Capacitors pretty much do the opposite.

If the power factor is correct, your meter tends to read exactly what you are using. If the power factor is wrong, it will read incorrectly. Power factor does not alter the amount of power you are using, simply the accuracy that a conventional meter will read it.

Now for someone who knows all about it to explain in a more coherent manner.....

[wyleu]

I'll have a go but it involves a bit of calculus;

There are three basic electronic components and most people know them as resistors, capacitors and inductors. But really they are devices that exhibit a relationship between the voltage put across them and the current that flows throu' them.

So to start with the simplest; The Resistor.  Normally a plastic tube with a carbon track cut round the outside, this is really a lossy wire.  If a DC voltage ( that has been given time to settle) is applied across the two ends of a resistor then electrons will move from one end of supplied voltage to the other via the resistor and if the potential difference is measured in volts and the current is measured in Amps then the relationship between the two is given by dear old ohm's law

   Potential Difference(Volts) = Current ( Amps) multiplied by Resistance (Ohms)

If the voltage goes up the current goes up; if the resistance goes up (the resistor warms up for instance ) then the current goes down. Now when we multiply the volts and the Amps we get the Power in Watts

   Power (Watts) = Current ( Amps) Multiplied by Potential Difference (Volts)

; so a 60 Watt lighbulb has an applied voltage of 240V and a current of 240 divided by 60 will flow or about a quarter of an amp.   

given we now know the current we can work out the resistance of the lighbulb when it's working ( it will be lower when it's cold) and it's 240 divided by 1/4    or about 960 ohms. (about 1 kilohm as it's also correctly known)


The other two components are a capacitor which is a device that is totally open circuit ( or at least it should be) consisting of two conductive plates placed one on top of the other with a non conductor of some specific sort placed between. Now if you apply a voltage across it as with the resistor once it has steadied then no current will flow; it's an open circuit but,one interesting effect of a capacitor is that if you remove the voltage supply the capacitor will maintain the voltage across itself. This is why they are used in central heating controls and such like cos they store energy. Now if you connect a resistor across our lonely capacitor a current will flow and it will do so but as you do so the voltage you measure across it will also fall until there are no volts across it. Now in this case the resistance will warm up and if we measured how much heat it gave out ( stuck it in a fluid and measured the increase in temperature we would be able to work out how much energy had been stored in the capacitor when it was disconnected from the battery.

All well and good it's a storage device, and it stores the energy as an electric field between the two plates

We now look at the third component; the Inductor or coil. This is precisely what is described in the second name a coil of wire often wrapped around another specific material, Because it is a piece of wire it will conduct very effectively any DC voltage you put across it, indeed it will act as a dead short circuit if you were to try and put a settled voltage across it to the detriment of the power supply. But it will store energy as with the capacitor, but it stores it in a magnetic field and if you do manage to arrange a steady power supply to keep a voltage across it a considerable current will flow and if you disconnected the battery the magnetic field would try to keep that current flowing and might well generate a fairly spectacular voltage in the process!

So why doesn't the inductor just leak thor' itself in that circumstance? well it's all down to the fact that capacitors and inductors don't ract to the steady voltage and current, it's the CHANGE in these quantities that demonstrates their characteristics. To avoid a lot of maths the current thro' a capacitor is a measurement called the capacitance multiplied by the rate of change of voltage across it. Big change of voltage big current, no change of voltage No current. The inductor is effectively the opposite the voltage across it is set by a quantity called the Inductance multiplied by the rate of change of the current. This are the old school favorites differentiation and integration.

Now if these two components are joined together then they can pla a very interesting game because the energy in one can travel out to the other where it will be stored and then if circumstances are arranged properly such that the circuit favours the flow the other way then the energy will flow back, and as long as there's no resistance around this merry dance can carry on for ever. The speed that it takes place is important because there is an optimum rate of flow for any values of inductance and capacitance and this is the called resonance and it's the basis of devices like oscillators and hence radio's and such like.
Now when the circuit is resonating the voltage across and the current flowing in the capacitor inductor pair will actually be perfectly opposite. The maximum current will occur at the minimum voltage and the maximum voltage will occur at the minimum current,  and because sine integrates to cosine and cosine integrates to sine( ignoring a sign here and there ) then the waveform you would observe this happening at in both cases would be a very beautiful sine wave at a frequency set by the value of the inductance and capacitance and nothing else.

If however you tried to apply a sine wave of a different frequency to the pair you would still get a certain degree of resonance but as it moves away from the frequency that the pair prefer the current and the voltage will respond in the only way they know how by shifting against each other. it would be similar to holding a G tuning fork against a D flat bell it would make a noise but it wouldn't be pleasant. This is how you end up with a situation where a circuit driven by the mains might appear to have a current flowing and a voltage across it , but because the power transfered into or out of a circuit is dependant of the product of voltage and current at any instantaneous moment the relationship between the two ideally needs to be peaking at the same time. and the Power factor is a measurement of this relationship. A power factor of 1 is a good thing. The voltage and current vary in sync and the load looks like a resistor. If however there is a preponderance of inductance or capacitance in the circuit the resonance of the circuitry will 'steal' energy during one peak and return it at the opposite peak so little actual transfer will go on although many electrons will be moving with all the appropriate waste.

Now any electrical engineer will  spot many flaws in the above piece but it's roughly what is going on. You change power factor by adding inductance or capacitance at the appropriate place to balance out the system. Power companies hate bad power factors cos if they get enough of it on their system they can be pumping out energy only to see it coming back at them, and also it can confuse the living daylights out of meters where not only can you rob Peter to pay Paul but also rip off what used to be the GEGB as well!

[kristen]

Pity you didn't teach me physics at school, I would have paid more attention!  Thanks for that.

So, if I have stuff like fridge motors and so on something that balances the Power Factor on my circuits could cause the electricity meter to read more accurately?

And by more accurately that also means LESS?

Kristen

[spongebobgreenpants]

Cheers for the explanations. ivan, i think i can get my head around what you are saying. wyleu, jaysus....you have made my brain hurt.

would i be correct in saying that i may benefit from such a device (if it actually works) in light of the chest freezer, fridge freezer and heat pump on my home circuit?

[roys]

Kristen

I could be wrong, but when I worked with the electricity board in the 80's I am fairly certain that meters in domestic installations did not take power factor into account, so if you did power factor correction at your home it will not make a blind bit of difference to your bill.  A domestic meter measures kW/h which is active (real) power.

So just to back up what wyleu is saying so well, Apparent Power is measured in kVA (volt amps) to distinquish it from the real power(kW).  Power Factor is the ratio of real power to apparent power so PF = real/apparent.  When real power is equal to apparent power as in a circuit only having resistance or one in which the capacitance is equal to inductance the power factor is equal to one.  A power factor of less than one indicates that not all the current is doing useful work.  If you understand this you are well on your way to passing your electrical principles exam
My head hurts now!!
Cheers Steve

[kristen]

So how do these things you plug in the ring main to "save electricity" work then?

I assumed it was to smooth the load of Fridges starting up and so on ...

[roys]

I will remain open minded or is that sceptical if it is saying that improving the power factor is going to save you cash.   mmmmm hope someone can prove that they do work and how.  Cheers Steve

[kristen]

" will remain open minded or is that sceptical if it is saying that improving the power factor is going to save you cash"

I was thinking of an earlier thread, which I've managed to track down:

>> Also i have the saverplugs for all fridges and freezer. these do work!!

http://navitron.org.uk/forum/index.php?topic=1658.0

Message from peter999  dated "Reply #9 on: July 03, 2007, 03:46:40 pm »"

which refers to this:

"Simply plug in the EPS 388. By reducing your house's 'power factor' (and applying other corrective techniques) it reduce your electricty bills by 10%-20%...Guaranteed. "

http://www.windtrap.co.uk/Energy-Saving-Products/Electric-Power-Saver-EPS-388.htm

"it comes with a Manufacturer's Guarantee If you don't save 10%-20% of your electricity bill in the 1st year you'll get your money back."

Seems like I can't-aford-not-to-have-one !! Although the grammar and spelling mistakes put me off a bit ...

Kristen

[roys]

I have e-mailed the company asking them to explain how it can reduce your bills by power factor correction if your meter can't 'see' reactive power.  Do you think they will reply?
Cheers Steve

[Paulh_Boats]

Roys,

Yes that is all correct - if the meter does not measure reactive power there is no problem.

And yes if inductive impedance matches capacitive impedance the power factor is 1 ..and reactive power is zero.

Capacitors and inductors both store power, but cancel each other out on AC circuits. Think of a childs see-saw - you need the same at both ends to balance the see-saw.... one unit of capacitance balances one unit of inductance.

So large steel mills with inductive motors will install capacitive motors just to balance the power factor closer to 1. Likewise these magic boxes will be capacitive to balance the inductance of fridge/freezer motors.

cheers
Paul

I could be wrong, but when I worked with the electricity board in the 80's I am fairly certain that meters in domestic installations did not take power factor into account, so if you did power factor correction at your home it will not make a blind bit of difference to your bill.  A domestic meter measures kW/h which is active (real) power.

So just to back up what wyleu is saying so well, Apparent Power is measured in kVA (volt amps) to distinquish it from the real power(kW).  Power Factor is the ratio of real power to apparent power so PF = real/apparent.  When real power is equal to apparent power as in a circuit only having resistance or one in which the capacitance is equal to inductance the power factor is equal to one.  A power factor of less than one indicates that not all the current is doing useful work.  If you understand this you are well on your way to passing your electrical principles exam
My head hurts now!!
Cheers Steve

[Gary T]

The manufacturer of the unit claim it optimises voltage, which could have a useful  effect on motors, and on old style fluorecent lights run off a capacitor, as they tend to run best at round 220V. The public information hoeveris vague, so I do not think it is actually doing this for wichit would have to be wired into the circuit. Several manufacturers sell commercial units for optimisin voltage.