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Netlist 11th March 2007 03:35 PM

Power factor calculation
How to calculate the ratio of resistive and reactive load if the impedance/resistance is not measurable?

As a practical example, Id like to measure the cos(phi) of an energy saving light bulb which states to consume 8W but measures 230V * 0.057A = 13.1W.
Of course, believing the manufacturer is the easiest, 13.1W 8W gives a power factor of 0.61 but I'd like to verify.
Out of circuit, the bulb has an infinite resistance probably caused by the internal ignition circuit.


sreten 11th March 2007 03:59 PM


Said bulbs have a complex supply / ignition circuit.
You cannot derive the power factor from that simple formula.

Only way I know of is a small additional resistor and an oscilloscope.


Netlist 11th March 2007 04:30 PM

Say a 10ohm resistor in series and go from there?


sreten 11th March 2007 05:11 PM


Yes. With an oscilloscope you can then see the current and
its relationship with input voltage. May not be continuous.


Netlist 11th March 2007 05:21 PM

Would there be a way to compensate these bulbs for a higher power factor. I calculated a 457F (!) capacitor would bring the power factor close to 1. Apart from the fact that its rather silly to do, I'm trying to get a grasp of the basic math.


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