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PC Power Supply Discussion Troubleshooting and discussion of computer power supplies

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Old 01-16-2007
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Default Which Components Use Which Rails?

I have always been wondering which components use EXACTLY which rails. By tracing the different colored wires from my PSU I think I have the breakdown but I COULD be wrong.

SATA: +3.3V (Orange), +12V (Yellow), +5V (Red)
Disk Drives (DVD): +12V (Yellow), +5V (Red)
Floppy: +5V (Red), +12V (Yellow)
Video Card: +12V (duh)
CPU: +12V
Memory: +5V, +3.3V
Fans: +5V (red) from molex, +12V from mobo????
Sound Card: ?????
USB devices: ?????
Pelletier Cooler: ?????
Water Cooling: ?????
LED/Cold Cathode: ?????

I have been trying to find the information all over the place but it seems I have not been able to find much. Can someone confirm this or maybe add to it?

Last edited by SKYMTL; 01-16-2007 at 12:13 PM.
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Old 01-16-2007
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Fans are always +12V. But for whatever reason, the wire is red coming from the mobo.

USB uses +5V.

Peltiers use +12V.

DC H2O pumps use +12V.

LED's typically use +5V, but the transformers used for CCFL's use +12V.
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Old 01-16-2007
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I'm guessing the wire is red to designate positive and negative.

Are all the other ones I listed correct?
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Old 01-16-2007
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USB = 5V
PCI = 3.3V and 5V I think on the last
Fans = 12V
Pelt = 12V or 24V depending upon the pelt
Water cooling (pump) either 12V or 120V AC depending upon the pump
CCFL = 12V
LED = 12V or 5V depending upon what rated resistor since LED's are typically < 3V (although most or all aftermarket, pre-built will use 12V)
Memory typically is 3.3V although some motherboards use a jumper to power it via the 5V rail (DFI, MSI)
Some fan controllers (analog) use 12V + 5V to vary the fan voltage, some (PWM) use strictly 12V and vary pulses of current to power the fan

There's more but I'm wiped out and it's not coming to mind.
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Old 01-16-2007
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Is there any site where I can find the actual power consumption of things like a sound card, DVD drive, fans and cathodes?
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Old 01-16-2007
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Quote:
Originally Posted by SKYMTL View Post
Is there any site where I can find the actual power consumption of things like a sound card, DVD drive, fans and cathodes?
DVD Drives and fans will have it on the unit.
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Old 01-16-2007
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And where would I find the actual power used by a processor? Or can I go by the TDP?

I really wish there was a website with all this....
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Old 01-16-2007
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Quote:
Originally Posted by SKYMTL View Post
And where would I find the actual power used by a processor?

I really wish there was a website with all this....
The rough hand estimate (some people like to argue with this method but when pressed none have ever provided a better method) way is to take the TDP and divide by 12 for current processors.
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So if a Conroe has a TDP of 65W, it is only drawing 5.4W of power? What can't be right. I think its more like 5.4A unless I'm mistaken.....
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Quote:
Originally Posted by SKYMTL View Post
So if a Conroe has a TDP of 65W, it is only drawing 5.4W of power? What can't be right. I think its more like 5.4A unless I'm mistaken.....
TDP/12v=Amps
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