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# PSU amperage on 12V rails

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December 14, 2008 6:37:42 AM

How do u calculate the Amperage on the 12V rails?(suppose one 12V rail has 17A and the other also has 17A in a 2 12V rail PSU)

More about : psu amperage 12v rails

December 14, 2008 1:08:51 PM

17*12+17*12
a b ) Power supply
December 14, 2008 1:34:38 PM

^ Wrong!!

It's 17+17 for your +12 amps.
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a b ) Power supply
December 14, 2008 2:02:48 PM

Shadow is Correct for the question you asked. yetyhunter provided power vs what you asked, current.

Some cavets you should be aware of:
The total of 2 x 17 = 34 A SHould be the correct answer, and would be for a "Quality" PSU. You need to look at the full specs for the PSU. 34 Amps x 12V = 408 Watts. Does this PSU show a full 408 W for the 12V. If it shows less then both 12V rails can not draw 17 Amps at the same time thus limiting the COMBINED current drain. A 2nd factor, espeacially on cheap PSU, is that they will also include a max power for say the +5V and +12 V. Normally this is not an issue. Another neg on cheapeee PSU is that this rating is at or near room temp. When you start drawing close to the max your PSU starts to heat up considerably and this can also drop the rating (Thermo derating)
a b ) Power supply
December 14, 2008 2:59:40 PM

^ Well said!
!