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Calculate the power of a fan

  1. Apr 18, 2007 #1
    Hi guys

    I suddenly think of a question. In my home, there's a standing fan which is old so I cannot see the nominal power on the label. With a ohm meter, can I identify the power of the fan? The meter can measure resistance R, potential U and current I of an AC power supply.
  2. jcsd
  3. Apr 18, 2007 #2


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    Current and voltage are what you need to measure.
  4. Apr 18, 2007 #3


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    Gold Member

    P = I^2 * R
  5. Apr 18, 2007 #4
    I am afraid those above formulae can only applied for the pure resistance appliances such as heaters or filament bulbs. The fan is not the case, it has inductance.
    Last edited: Apr 18, 2007
  6. Apr 21, 2007 #5
    [tex]P = I \cdot U[/tex] would be ok.
    Last edited: Apr 21, 2007
  7. Apr 23, 2007 #6
    [tex]P=UIcos\ \phi[/tex] even better.
  8. Apr 23, 2007 #7
    thanks all for posting here. Then my question is how can I identify the phase lag angular phi with only a VAOhm meter?
  9. Apr 23, 2007 #8


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    You would need an o-scope or something like a hand held Fluke meter.
  10. May 12, 2007 #9

    this will give you the power produced by the motor

    but it will not give the real power of the fan....

    which is power=Tw

    fan power will be a little less than motor power and this due fraction(energy conv.)
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