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# Power Supply Calculations

## Power Supply Calculations

(OP)
Hi,

If you have a Power supply, that supplies a load of 15Amps at 13.8VDC, how would you calculate the current on the AC side of the supply (@240V). (this information could help with circuit breaker sizing etc?)

If you have to assume an efficiency for the power supply and a input power factor, lets say 90% efficiency and 0.95 pf.

Thankyou

### RE: Power Supply Calculations

OK, so apply conservation of energy.  Don't forget to include a power factor correction, though...

### RE: Power Supply Calculations

How is it possible a practicing engineer (or even a first-year EE student) could ask such a basic question?

Dan - Owner
http://www.Hi-TecDesigns.com

### RE: Power Supply Calculations

(OP)
Hi,

15Amps at 13.8VDC = 207W

90% efficiency....power on AC side = 230W

P = V*I*pf
230 = 240*I*0.95

I = 1.009A???

Would this we the correct answer?

Sorry Macgyver, this was a discussion I was having with a friend and thought we would get a confirmation.

### RE: Power Supply Calculations

Hello all,

@Camomac, you got it right in the calculation. However, it holds good only for a 1-Ph system as the input. For a 3-Ph system, dont forget to add "Root 3" to the formula.

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