Power Calculation

Thread Starter

keyboardcowboy

Joined Dec 31, 2012
25
The label on an air conditioner reads the following

Voltage: 220v
Current Rating: 9.8 Amps

If i am to calculate the power consumption, will i just multiply the current and the voltage?. The thing that i do not understand is since this is AC wouldn't i consider the power factor in the power calculation, but then again another thing is if the power factor would have mattered wouldn't the manufacturer have mentioned the PF on the label :confused::confused:
 

mitko89

Joined Sep 20, 2012
127
Ask yourself the questions: 9.8 Amps what - P-P, RMS? Does your air conditioner have a huge internal capacitance and inductance so the power factor is an issue? Do you think if it had such a issue the manufacturer wouldn't bother to correct the pf?
 

alfacliff

Joined Dec 13, 2013
2,458
it dosnt have to have huge inductors or capacitors to affect power factor, a loaded or unloaded induction motor will change power factor.
current and voltage on labels is usually rms, not peak to peak. simple multiplication of volts and amps will give you watts but then you have to understand thats running power, not startng power.
 

crutschow

Joined Mar 14, 2008
38,505
Multiplying the volts and amps will give the VA not watts since, as you noted, the PF needs to be known to get watts. The PF is normally not a big concern for small home appliances so is not given. The amps are given for sizing of the circuit and fuses/breakers. Typically a fully loaded AC induction motor has a PF of .85-.9 so the actual power consumption would be 10%-15% less than the VA.
 

kubeek

Joined Sep 20, 2005
5,796
The 9.8A will most likely be maximum current consumption so that you can properly size your breakers and wiring. It will vary depending how many fans and motors are running at a time.
 

NorthGuy

Joined Jun 28, 2014
611
You cannot calculate power consumption from the label with any reasonable precision. It has bad power factor (it's a motor). It cycles. It might be variable speed. The label is not very accurate.

The best way is to buy a Kill-A-Watt meter and measure directly.
 
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