PSU Amp calculation

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November 14, 2010 8:50:11 AM

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?

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a b ) Power supply
November 14, 2010 9:46:43 AM

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.
a c 80 ) Power supply
November 14, 2010 9:48:23 AM

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.
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a c 80 ) Power supply
November 14, 2010 10:41:09 AM

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.
November 14, 2010 10:48:25 AM

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
a c 80 ) Power supply
November 14, 2010 10:50:09 AM

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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