Fan Power Consumption

Discussion in 'Electronic Repair' started by Joe, Jul 17, 2007.

1. 120v 2.2amp = 264 watts

Compare that to the wattage you measured (>>> 99/136/196 watts) and you
can see why I said that whatever the plate says is not very accurate.

2. This is not watts; it's volt-amps.
You should compare it to the volt-amps he measured. Then it's not so far
off.
You are making a mistaken assumption. If you measure the current draw
(amps) and the applied voltage separately, and multiply them, you get the
(real) watts consumed *only* if the load is a pure resistance. If the load
has a reactive component (inductance or capacitance; in this case the motor
is an inductive load), then the product of volts and amps is the "apparent
power" (volt-amps), not the "real power". See:
http://en.wikipedia.org/wiki/Power_factor

An incandescent light bulb, electric stove, electric toaster or electric
blanket would be an example of a pure resistance load. Most household
equipment other than heating devices, if they have motors (refrigerator,
for example) or non-PF corrected power supplies (older computer or
television) will have a power factor of less than 1, and will require a
special type of meter (a wattmeter) to measure their real power consumption
(because the load has a so-called "wattless" component):
http://en.wikipedia.org/wiki/Wattmeter

As they say on that page, "On an ac circuit the deflection is
proportional to the average instantaneous product of voltage and current,
thus measuring true (real--my addition) power, and possibly (depending on
simply multiplying the readings showing on a stand-alone voltmeter and a
stand-alone ammeter in the same circuit."

Go back and look at Bill's earlier post where he gives the result of his
actual measurements:

"99/136/196 watts
129/175/248 volt-amps
at 121 volts"

You'll see that volt-amps and watts are substantially different. This is
the beauty of the Kill-A-Watt. It measures both the apparent power and the
true power. The apparent power (the product of separately measured amps
and volts, remember) will be larger than the true power with a fan motor  