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You may have seen little plastic boxes with a plug poking out and the words “Power Saver” in friendly letters on the outside. You may also see claims that these devices can save up to 40% of your power bill. It all sounds like snake oil stuff doesn't it? Rather like that magic liquid you put in your petrol tank and it fully overhauls your engine, services the brakes and balances the wheels while you drive along. So what are these power savers and more importantly “do they work?”
Let us first consider TF.
TF, as everyone knows, stands for “Thirst Factor” and is the thirst quenching capacity of a pint of very best bitter. Any good pint of beer has a good head on it but the froth itself is not going to quench much thirst now is it? The froth represents an inefficiency in thirst quenching terms.This means that the thirst quenching capacity of a glass of beer is less than the capacity the glass can hold, it is in fact the capacity of the glass less the volume taken up by the froth. The TF is the ratio of the amount of thirst quenching liquid to the volume of the glass. Low TF is well understood in English pubs where many a landlord has been dragged over the bar with the friendly words “Ey, call that a pint you cheating b......d.”
Now let us consider a thing called “Power Factor”.
Imagine Fred is pulling a box along the ground (don't ask me what it is or where he is going or you might get a rude answer). Fred is 6 feet tall and has a rope over his shoulder which is tied to the box which is only 1 foot high - the rope is sloping. The box is being pulled horizontally along the ground but he is pulling the rope at an angle. This means some of his energy is wasted pulling the box upwards. Now if Fred was a very small dwarf and the height of his shoulder was the same height as the centre of the box (yes I know this is totally ridiculous especially when we still don't know what is in the box or where he is going) then the rope would be horizontal and all his effort would be pulling in the direction the box is moving - this is more efficient. The horizontal rope has a power factor of 1 and the sloping rope has a power factor less than one - some power is wasted.
If we apply this analogy to electrical circuits, Electricity running through an electric motor or transformer creates a magnetic field to a) create movement (in the case of the motor) or to b) induce an electrical current (in the case of a transformer). In both cases there is inefficiency, some power is needed to create the magnetic field. This lost power is called “Reactive Power”.
Electrical engineers talk in terms of KVA (kilo volt amps) as the power we put in, KW (kilo watts) as the useful power we get out and a thing called KVAR (reactive kilo volt amps) as the lost power through inefficiency. The ratio of the power we put in KVA to the power we get out KW is called the “Power Factor”.
If you are totally lost or bored by now, that is alright. You can go and have a good lie down or even better check the TF of the contents of your fridge. If you are keeping up with this then perhaps you might be able to explain it to me, I lost the thread a while ago.
In our present electrical supply difficulties many people have taken a sudden interest in generators. They will have come to know that the size of a generator is given not in KW (kilowatts) but in KVA (kilovoltamps). If you buy a generator you need to know that you must buy one with a power rating greater than you need. Why? Well because a 10 KVA generator may give you an output of only 8 or 8.5 usable kilowatts of power. This is because of the “Power Factor” and the loss of some of the energy in creating the magnetic field to generate the electricity.
Alright so now I have lost you (and myself) totally, the fridge has a TF of zero so we had better move on.
In large industrial plants where many large electric motors are used the loss of power through inefficiencies adds up and can cost a lot of money. Electricity supply companies in many parts of the world calculate the power factor of their customers and penalise them if they are inefficient. To save money and electricity electrical engineers have worked hard at making electric motors more efficient. They have also found a way of cancelling out the reactive power loss.
They use an electrical component which, as everyone knows, is called a capacitor. Clever little blighters, capacitors. What they do is they sit there in the electrical circuit and they collect those zippy little electrons then every now and again, when they've got a belly full, they spew a few out. The capacity of a capacitor is rather like the capacity of teenage drinkers and is determined by the capacity they can hold before they spew.
So there you are with your 85% full beerglass with a TF of 0.85, the young fella next to you throws up displacing your froth, your glass is now full and you have a TF of 1 (in theory).
In an electrical circuit adding a capacitor into the circuit has a tendency to balance out the lost reactive power. This reduces the power consumption and also reduces the power load on the circuit. Large industrial operations use capacitors extensively to reduce power loss in electric motors. It is important that the capacitors are carefully matched to the motors they are connected to. Incidentally electric motors that are not working very hard are a lot less efficient, they have a lower power factor than motors that are working at their hardest.
So how does all this blather affect us (apart from advising us to keep away from drunken young men in pubs)?
Anything electrical that works by creating a magnetic field may benefit from the addition of capacitors in the electrical circuit. This means anything with motors such as water pumps, pool pumps, air conditioners, electric fans and electric toothbrushes, or anything with transformers such as flourescent lights, computers and televisions.
Electrical devices that do not produce a magnetic field such as water heaters, electric kettles and hairdryers do not have this reactive power loss and so do not benefit from the use of capacitors.
As already stated in industrial situations electrical engineers calculate where and what should be installed. For housing circuits you can buy capacitors branded as “Power Savers” which you simply plug into an electrical plug socket.
How well these devices work depends on many factors and is difficult to determine. Certainly the claim on the packaging of up to 40% is stretching the belief cells in my brain however let me tell you a story.
A good friend of mine has a small house, he has 1,300 watts and is right on the limit of his power supply. If his well pump switches on while he has his air conditioner running the surge in power makes his PLN circuit breaker cut out. He recently bought a power saver and since he started using it the circuit breaker only rarely cuts out which suggests that the power saver does reduce the loads on the circuits and may well help to reduce the surge in power that you get when an electric motor in a pump starts up.
It should be noted that with the current PLN difficulties voltages are dropping to very low levels (I recently heard of 130 volts!) and this results in higher currents which can make even robust electrical circuits cut out.
So do Power Savers work? Well yes they do and the theory is there to back them up. How effective they are is another matter and for individuals is probably very much dependent on their own household circumstances. Savings on electrical bills may also be questionable and, unless you are running many air conditioners and water pumps, very likely not “major'. Having said that my friend is very pleased to be able to run his air conditioner with only occasional power cutout. He is well satisfied with the Rp400,000 investment.
If you are using a Power Saver let me know of your experience, good or bad, and perhaps we can all find out just how effective they are.
Alright so now you are totally bored, Fred has arrived with his box and it is time to go checking a few TFs.
Phil Wilson
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