# Calculate the power of a fan

1. Apr 18, 2007

### pixel01

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. Apr 18, 2007

### FredGarvin

Current and voltage are what you need to measure.

3. Apr 18, 2007

### Mech_Engineer

P = I^2 * R

4. Apr 18, 2007

### pixel01

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
5. Apr 21, 2007

### sstone

$$P = I \cdot U$$ would be ok.

Last edited: Apr 21, 2007
6. Apr 23, 2007

### zoki85

$$P=UIcos\ \phi$$ even better.

7. Apr 23, 2007

### pixel01

thanks all for posting here. Then my question is how can I identify the phase lag angular phi with only a VAOhm meter?

8. Apr 23, 2007

### FredGarvin

You would need an o-scope or something like a hand held Fluke meter.

9. May 12, 2007

### Mech. Engineer

Power=I*U

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.)