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Fan Power Consumption

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

  1. Vey

    Vey Guest

    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. The Phantom

    The Phantom Guest

    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
    load characteristics) showing a different reading to that obtained by
    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
    load, but the true power reading is what you pay for on your electric bill
    (if you're a typical residential customer). Large industrial customers pay
    a penalty if the apparent power they consume is larger than the true power,
    but ordinary residences don't.
     
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