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Power Supply for Fans Only

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Jan 26, 2001
Hey everyone, got a quick question.

I installed a second power supply to power several fans, used an AT style, mounted push-button on back of case, and everything fits in case correctly. My question, I powered it up after connecting my fans to it, and they seem much slower than normal. (Much Quieter, but 1/2 as powerful).

So I grabbed the handy voltmeter, and tested the voltage output. 12 volts.
I tested the 3-pin motherboard plug, 30 volts. No wonder! Less than half the voltage!!

So, how do I operate the fans off the new power supply at the proper voltage?? You guys got me, I'm REALLY new at this whole thing and the whole idea is starting to sound really dumb.

My object was to run my 7 or 8 fans off a seperate 250W PS that I had laying around to free up power for all my drives and mobo.

If you have a solution or ANY advise PLEASE let me know. Thanks in advanced.

Run-em cool.
_____________________________________________________________________________________T-Bird 950@1180
Asus A7V133A
320 Mb Micron PC133
Voodoo 5 5500 166@208
Where are you measuring 30 volts? There's no 30 volt supply in a PC supply. The fans should be running on the 12v output.
I measured 30 volts from the 3 pin socket-type fan plug on the top of the motherboard labeled "PWR_FAN"

This would possibly explain why the fan was running at a faster rate of speed when mounted here opoosed to the seperate power supply at 12 Volts.
Alright, 30v sounds off the wall...when I read that I was like WTF? So be for I wrote this I decided to check for myself...I measured 12v and 3v off the Pwr_fan 3pin socket on my asus mobo...so either you read your meter wrong or AMD mobos are totally different...anybody got his mobo that can confirm his readings?

A stand alone ATX or AT power supply will not put out 12v unless you put a 1 amp load on the 5v lead...so either throw a resistor or a LED in there...
Yeah I couldn't believe it either, I tried it again, same damned thing.

But, when I meter off a regular 4-pin plug, and use the Yellow lead and a ground, I get 30 volts from that as well. Then I switch to the Red lead and ground, 12V, ???

I think something really might be F'd up, either that or I inadvertantly found a way to "Supercharge" my motherboard. (Hehe not likely)

I plugged the fans into the Yellow lead and the ground and not they are really whirring, am I putting too much power to them?

Thanks a lot, I really appreciate the help!
Ya 30v is wayyyy too much to be putting into your fans...I'm surprised you haven't fried them yet...