Average Power of A.C.: Assume Phase Difference Zero?

[kelvin490]

We know that the average power of A.C. is IVcosθ, where I and V are RMS and θ is the phase difference. I would like to ask in common application, such as power of a lamp, computer, fan etc. Can we simply assume the phase difference is zero and get a fairly accurate answer? Thank you.

 

[mjhilger]

I'm sure others with more knowledge in this area will post a better response. Power Factor for switching power supplies that qualify for UL or other certs control the PF so essentially (0 - EDIT, this should be 1) for that one. Incandescent light bulbs are for the most part (0 - EDIT this should be 1) as well. Fans or other motor appliances are probably not. There are/were devices that are sold to view the power factor (watt wizzard I think was one) and other devices that are suppose to compensate to yield lower usage for those devices.

So to answer your question, no I don't think you can assume a power factor of (0 - EDIT this should be 1) because one location may have many fans, or other devices that might cause a 5 - 10% difference. However, if your location is just electronics and lights you might be able to assume PF of (0 - EDIT this should be 1).

Others will chime in and provide a better answer.

 

[Baluncore]

The power factor of a resistive or a perfectly corrected load is 1.00
The PF of a lossless inductor or capacitor is zero.

You can assume that all higher power equipment will have a PF better than 0.8
Very small items may have a worse PF but they will only be using small amounts of AC current.

So you can assume PF is 0.9 +/– 0.1 for any approved electrical product.
You can only assume for filament lamps and resistive element heaters that PF = 1.00

 

[mjhilger]

Baluncore, thank you. Many years since I used PF remember the concepts, but the number slipped my mind. I should have looked up. Thank you for the correction.

 

[alphy]

I cannot make assumptions without proper data and evidence. The phase difference between current and voltage is a crucial factor in determining the average power of an AC circuit. While it is true that in some common applications such as powering a lamp or a fan, the phase difference may be close to zero, it is not always the case. In more complex circuits, the phase difference can vary and significantly impact the average power calculation.

To ensure accuracy, it is important to measure the phase difference using appropriate instruments. Making assumptions can lead to errors and incorrect calculations. Therefore, it is always recommended to measure and consider the phase difference when calculating the average power of an AC circuit.