How to find electricity usage of a PSU ?

[Quad]

my ultimate goal is to find the electricity usage of a psu in kwh.

if a psu pumps out 300w, and it is known that its efficiency is about 70%, how would you figure out how much electricity it uses?

thx in advance

 

[ApacheXMD]

One Watt is a Joule per second, where a Joule is a quantity of energy. That means a watt is a power unit (energy per unit time)
If you have a 300 watt power supply, and it's efficiency is 70 percent, that means you have to put in 428.57 watts to get that 300 watts out (300/0.7=428.57).

428.57 watts is 0.42857 kilowatts. So lets say you run the computer all day long (24 hours), you would use up 10.29 kilowatt-hours of energy (24*0.42857=10.29).

But keep in mind that your powersupply isn't gonna be outputting 300watts at all times. That's the MAX power rating, and you'd probably kill the powersupply if you ran it at that level all the time.

-patchy

 

[Quad]

ahhh excellent

that's exactly what i was thinking =)

thx patch for confirming

 

[4824guy]

I would thing that you would really have to know how much current the PS is actually using. Just because it is rated for 300watts doesn't mean anything.

I am thinking you would have to measure the AC current actually being used with a meter.

Then using the standard Ohm's law
power(watts)=voltage(volts) times current(amps)