Hi Don,
A little off the subject but could you give us a long form explanation of Power Factor?
73, John in Tucson
Don is so much better than I at explaining things, I'll be interested in reading his explaination too.
But meanwhile, I'll give it a shot.
Powerfactor applies to the phase angle between current and voltage in AC circuits.
When you attach a pure resistive load to an AC circuit, like an incandescant bulb for example, the current and voltage in the circuit are in phase. The RMS volt * amps (VA) flowing in the circuit equals the power in Watts delivered to the load and the power factor is 1.0.
Now if instead, you have a purely reative load, like attaching an inductor or capacitor across the AC circuit, you also have a current flowing.
But in this case, the current and the voltage are out of phase. What is happening, is during part of the cycle as the voltage rises, the current decreases until part of the way through the cycle, the current reverses and then flows the other way during the other part of the cycle.
So during 1/2 the cycle power is being delivered by the wall socket to the load and during the other half, the load is delivering power back into the wall socket.
In a purely reactive load, the VA may be the same as with a resistive load -- and a current meter would read the same -- but the power factor is 0 so no power is consumed from your utility company and your electric meter doesn't charge you anything.
In effect, you are charging the capacitor (in the case of a capacitive load) across the line for half the cycle, and then the capacitor is discarging and putting power back into the line during other half the cycle -- with the net result that no power is consumed.
Most real world devices have a power factor between 0 and 1 and are either partially capacitive or partially inductive.
In these cases, you need to use the formula below to determine the power consumed by the device:
Power consumed in Watts = RMS voltage of the AC circuit x Amps x F
Where F is the power factor.
Dave
