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device that saves power consumption.

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alphacat

New Member
Hello.
I've heard on a device (I think it was developed in Mexico) that saves power consumption.
The nature of the device is to connect between the appliance and the AC mains, and somehow it saves power.
Does anyone know how can a deviec save power consumption, not necessarily this one but in general?

I know about devices that save standby consumption, but I think that the mentioned device save power consumptuin while device is working.

Thank you.
 
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Hero999

Banned
I've seen something similar before.

It doesn't actually reduce the power consumption, it merely corrects the power factor which reduces the current and creates the illusion of the device drawing less power.

They are good for the environment because lower current means lower I²R losses. Unfortunately you won't save any money on your bill because most companies charge for real power not apparent power (VA). Some companies might want to consider it because large businesses can be fined for having a poor power factor.
 

alphacat

New Member
Thank you very much.
That sounds very interesting.

I'd like to ask you 2 questions please regarding that:
1. This device you're talking about increases power factor, so therefore since P and V remain the same then I decreases? (I=P/[V*PF])


2. Could you explain please how they increase the power factor of the appliance connected to the device?
 
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dknguyen

Well-Known Member
Most Helpful Member
Power is proportional voltage and current multiplying together (The voltage and current "stack up" on each other to produce power). When both are sine waves they stack up differently. If both waves are in phase, then all the peaks happen at the same time and the zeroes happen at the same time. The two sine waves "stack up" on each other to produce the power. If they are completely out of phase (90 degrees phase shift) then the peaks of one wave happens during the zero the other and you get zero power because anythng multiplied by zero is still zero.

The more in phase the current and voltage sine waves are, the more actual power you can get from it. The apparent power is "the maximum potential power" you can get and is the power you will get if the sine waves are in phase. The real power is how much power you actually get due to the voltage and current being phase shifted.

Increasing power factor means you shift either the current or the voltage sine wave so it is more in synch with the other sine wave.

Stare at these pictures carefully.
File:power factor 0.svg - Wikipedia, the free encyclopedia
File:power factor 0.7.svg - Wikipedia, the free encyclopedia
 
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alphacat

New Member
Thanks.
So you're saying that the device shifts the voltage or the current (which one of them)?

Could you please also verify what I said on 1?
 
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crutschow

Well-Known Member
Most Helpful Member
Thank you very much.
That sounds very interesting.

I'd like to ask you 2 questions please regarding that:
1. This device you're talking about increases power factor, so therefore since P and V remain the same then I decreases? (I=P/[V*PF])


2. Could you explain please how they increase the power factor of the appliance connected to the device?
1. It actually reduces the voltage to reduce the current (see 2.)

2. They automatically reduce the motor voltage to the minimum required for the load it is driving. This reduces the inductive (reactive) portion of the motor current which, in turn, reduces the I²R power loss in the motor winding resistance. Thus the motor operates more efficiently and it does actually save a small amount of power.

I tried one on my refrigerator a few years ago, but took it back because it caused interference in my AM radio (it uses a Triac to regulate the voltage which can generate RFI, similar to a light dimmer). If you never listen to AM radio it probably wouldn't be a problem
 
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dknguyen

Well-Known Member
Most Helpful Member
Thanks.
So you're saying that the device shifts the voltage or the current (which one of them)?

Could you please also verify what I said on 1?
It shifts one of them but it doesn't matter which one, The only thing that matters is the way they shift relative to each other (you could shift just one, or you could shift both in opposite directions by half as much). Which one that is actually shifted depends on the device.

Power factor is the measure of how much the voltage and current are cooperating together to produce power. THe more they cooperate the more actual power they produce.

If you don't understand power factor, here is an analogy for voltage sine waves and current sine waves and how their phase relationship affects power:

It's like two people pushing a car that is too heavy for one person to push. If you push together and rest together (in phase) then the car has the fastest average speed. If one person pushes while the other rests (90 degrees out of phase), the car doesn't move at all. If you make it so the periods of resting and pushing slightly overlap between the two people, the car moves will have a slow average speed. The more overlap there is where two people push together (and rest together) means the car has a faster and fastser average speed (until you get to the maximum average speed where the two people always push the car together and resting together).

The two people are Voltage and Current, and the average speed of the car is called power. Pushing is the positive and the negative peak of the sine wave and zero is resting. The actual average speed of the car is the actual power, and the maximum possible average speed of the car is the apparent power. The ratio between actual speed and maximum speed is apparent power.

Remember, there are TWO power values- the actual power and the apparent (maximum possible) power. And the voltage and current are sine waves, not constant DC.
 
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crutschow

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The two people are Voltage and Current, and the average speed of the car is called power. Pushing is either the positive or negative peak of the sine wave (pick one, it doesn't matter) and the other peak is the resting.
More accurately the resting time is when the voltage is zero and the positive and negative peaks are when the maximum pushing occurs. (From a voltage/current point of view, both positive and negative voltages produce power. A negative voltage produces a negative current which, when multiplied together, give positive power).
 

dknguyen

Well-Known Member
Most Helpful Member
I thought something was weird when I said that about positive and negative peak making zero power. SOmehow I got the idea stuck in my head that 180 degrees phase shift was zero power factor but that doesn't make sense when you look at cosine and sine. It's probably because I was adding the sine waves in my head instead of multiplying them. It's supposed to be 90 degrees phase shift makes zero power factor (zero actual power). *Fixed all my posts in this thread that referred to that*

THanks.
 
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alphacat

New Member
It shifts one of them but it doesn't matter which one, The only thing that matters is the way they shift relative to each other (you could shift just one, or you could shift both in opposite directions by half as much). Which one that is actually shifted depends on the device.

Power factor is the measure of how much the voltage and current are cooperating together to produce power. THe more they cooperate the more actual power they produce.

If you don't understand power factor, here is an analogy for voltage sine waves and current sine waves and how their phase relationship affects power:

It's like two people pushing a car that is too heavy for one person to push. If you push together and rest together (in phase) then the car has the fastest average speed. If one person pushes while the other rests (90 degrees out of phase), the car doesn't move at all. If you make it so the periods of resting and pushing slightly overlap between the two people, the car moves will have a slow average speed. The more overlap there is where two people push together (and rest together) means the car has a faster and fastser average speed (until you get to the maximum average speed where the two people always push the car together and resting together).

The two people are Voltage and Current, and the average speed of the car is called power. Pushing is the positive and the negative peak of the sine wave and zero is resting. The actual average speed of the car is the actual power, and the maximum possible average speed of the car is the apparent power. The ratio between actual speed and maximum speed is apparent power.

Remember, there are TWO power values- the actual power and the apparent (maximum possible) power. And the voltage and current are sine waves, not constant DC.
Thank you for the wonderful explanation about power factor :)
Its great!



They automatically reduce the motor voltage to the minimum required for the load it is driving. This reduces the inductive (reactive) portion of the motor current which, in turn, reduces the I²R power loss in the motor winding resistance. Thus the motor operates more efficiently and it does actually save a small amount of power.
Thank you! that was just what i was looking for.
You mean that the device can reduce power consumption of motors only, right?
It is very interesting
- How does the device "calculate" the minumum voltage requiered for the motor to drive its load?
- How does the device reduce the motor's voltage, using a transformer? (it must be something that will consume zero power).

Thank you again. :)
 
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dknguyen

Well-Known Member
Most Helpful Member
It would be a self-adjusting variable capacitor or a capacitor bank where capacitors with switches that are turned on and off to change the effective capacitance. THe non-unity power factor (unity = 1 which is the ideal power factor) is because inductors (like the winding inductance in the motor) causes the current to lag the voltage making a phase shift. Capacitors cause voltage to lag the current making a phase shift that is opposite of an inductor. If you put the two together in the right amount, they cancel each other out. The capacitance is adjusted to keep the power factor as close to 1 as possible at all times.

THere are many other more complicated ways to correct power factor for more complicated situtations.
 
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audioguru

Well-Known Member
Most Helpful Member
Most "power reducing gadgets" are just an over-priced capacitor.
If the value of the capacitor matches the amount of imductance of your appliances that are running then the power factor is better and your electrical utility company saves money (you don't save anything). But chances are that the value of the capacitor is not correct.
 

fernando_g

New Member
In equation form:

P= V×I×cosθ
where θ is the angle between voltage and current, and its cosine is called power factor.

For inductive devices (i.e electrical motors) the current lags the voltage.
For capacitive devices, the current leads the voltage.

Therefore, if you apply a capacitor to a motor, the lead and the lag angles tend to cancel each other...this is called power factor correction.

Electric utilities do not penalize low power factors at homes. For large electrical users, like businesses and industry, they do, and it costs them a lot of money to have a low power factor.

Therefore you'll always see a bank of power factor-correcting capacitors in those applications.
 
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