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-12V rail variation?

  • Power Supplies
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  • Homebuilt
  • Components
Last response: in Components
March 13, 2010 12:43:39 PM

Hey folks,

I have a faulty build (as stated in my general homebuilt thread ). One of the suggestions to find out what is wrong with my build was to measure the voltage on my Corsair tx650 rails. I used the paper-clip jump start to test the PSU on it's own and all of the voltages were within the +-5% difference from the stated specification, except for the -12V rail which was off by 1,1V. I tried looking up the possible voltage differences on the -12V rail but all I could find is the variations of the 3,3V,5V and 12V.

So my question is, does any of you know what the possible variations on the -12V rail are and how much of a problem it might be if it is off by 10%?

More about : 12v rail variation

March 13, 2010 1:32:07 PM

Uh, most modern PCs (including the PhII and the associated platform) rarely ever touch the -12V line. My motherboard (ASUS P7P55D EVO) completely ignores the -12V line. That's why PSU makers have been lax with the -12V voltage, with some even rising up to -8V without causing issues.

So to sum it all up: your -12V line could be disconnected and your system would work just fine.
March 13, 2010 4:16:09 PM

Alrighty then, thanks mate.
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March 14, 2010 7:02:04 AM

The voltage tolerance on the -12 volt rail is 10% instead of 5%.

Here are the official atx power supply voltage rail tolerances:

Voltage Rail Tolerance
+5VDC ± 5 %
-5VDC (if used) ± 10 %
+12VDC ± 5 %
-12VDC ± 10 %
+3.3VDC ± 5 %
+5VSB ± 5 %

The -5 volt rail has been deleted in the newest atx standards. The -12 volt rail is just about gone too. The -12 volt rail used to supply power to a few motherboard components such as the old serial port circuits. Most modern motherboards no longer use the -12 volt rail.
March 14, 2010 11:00:01 AM

Great, thanks for the detailed answer Johnny.