# Power Calculation

Discussion in 'General Electronics Chat' started by keyboardcowboy, Jul 30, 2014.

1. ### keyboardcowboy Thread Starter New Member

Dec 31, 2012
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0
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

2. ### mitko89 Member

Sep 20, 2012
123
19
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?

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3. ### alfacliff Well-Known Member

Dec 13, 2013
2,449
432
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.

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4. ### mitko89 Member

Sep 20, 2012
123
19
My questions were to guide him what exactly he can do with his input data and to make a simple assumption.

5. ### crutschow Expert

Mar 14, 2008
21,996
6,358
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.

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6. ### alfacliff Well-Known Member

Dec 13, 2013
2,449
432
since power consumption is measured in va, not watts, and pf is not given, simple multiplication is enough.

7. ### crutschow Expert

Mar 14, 2008
21,996
6,358
The power meter on your house measures watts, not VA. It ignores the reactive part of the current.

8. ### kubeek Expert

Sep 20, 2005
5,506
1,058
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.

9. ### NorthGuy Active Member

Jun 28, 2014
611
123
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.