PSU Amp calculation

Based on this thread

What mactronix said:

"you haev to divide the total wattage of the rails by the Voltage which equals the actual Amps. "

Is this true for Single rail too? :)

And how do you calculate single rail amps?
6 answers Last reply
More about calculation
  1. watts / volts=amps.
    amps x volts=watts.
    The problem is with power supplies with 2 or more 12v rails.Where each one is rated at 17amps. 17 +17=34. but the maximum combined for the 2 is 27. so if one is pulling the max of 17 the other will be limited to 10.
  2. Yes its true, and easier for single rails. If a single rail PSU can output 360W on the 12V rail, then 360W / 12V = 30A. The math is clear and simple. Its the multi rail PSUs that are problematic as you need to find the total wattage putput, and not all PSUs make this easy.
  3. SO if we take Corsair TX850 PSU.

    Does that means:

    840w - 180w = 660w /12v = 55A

    Is this correct?
  4. Probably not. Corsair is probably using a DC to DC conversion for the minor rails. (your link isn't working so I don't know.) You can probably divide by 12 the 840W.
  5. sorry i dunno whats wrong with the link but its a spec of it so Corsair TX850 PSU has:

    +5v@30A, +3,3v@30A = 180w
    Single +12@70A = 840w

    840w - 180w = 660w /12v = 55A?

    becuase mactronix said you have to do take +5v and +3,3v Wattage minus +12v wattage than devide that by 12?

    or i got it wrong xD
  6. No, 70A. It obviously can't output all 70A if you are using a lot of 5V or 3.3V devices. As I said they are using DC to DC to give you the minor rails. Its a single rail, so the total possible output is 70A.
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