My weird cooling situation

[EnzoM3]

Actually not mine, but a friend's situation that I'm helping out with.

He keeps his PC inside a cabinet in his desk. The cabinet's door stays closed so it gets pretty hot in there. About two years ago he asked me if there is anything to do about it. I eventually figured out a way. I drilled out two holes the size of 80mm case fans and mounted two fans. One on the bottom that pushed cool air in, and one on the top to pull hot air out. I took out one of the PCI slot's cover, and run a couple 4-pin extensions cables from the power supply to the fans to power them. It worked beautifully and everything stayed cool, the fans only run when the PC is on.

Last week he finally bought a new PC to replace the old one. The new one is a slim form factor, and to my dismay, the power supply doesn't even have any 4 pin connectors. It only has two SATA connectors (one for DVD and one for HD) and the motherboard connectors. I thought about just putting an old power supply in the cabinet to power the fans, but realized the stand alone power supply won't turn on by itself, it has to be turned on by the motherboard.

I can only think of one idea. Find out which pins on the motherboard connector turned it on, and short them so it's always on. I found a bit info here:

http://pinouts.ru/Power/atxpower_pinout.shtml

It says to short the PS_ON pin to GND to turn on the power supply. There are a bunch GND pins, does it matter which one I use?

Any other ideas about this? I don't have to stick to the PC case fans, but ideally the fan only turns on when the PC is on. If not, then at least a way to turn the fans off manually without having to deal with wires. I guess I could use a second power strip for the stand alone power supply and use it to turn it on and off after shorting the PS_ON pin.

Thanks,

Jim

 

[Zap]

Green to ground. AFAIK doesn't matter which ground.

You can also repurpose an old wall wart as long as it is somewhere in the 9-12v range and has enough amperage to keep both fans spinning. Just leave it on all the time, especially if it is 9v and quiet enough.

 

[gorobei]

you could rewire a usb cable to run the fans. there are a bunch of tutorials out there for this.

 

[ehume]

Won't the USB cable provide 5v?

Wall bricks work fine, as long as the fans draw enough current to keep the volts in line. As the guy said above, 9v is about right: you'll avoid overvolting your fans (you can overvolt fans with a wall brick; I did).

 

[MoMeanMugs]

Won't the USB cable provide 5v?

Wall bricks work fine, as long as the fans draw enough current to keep the volts in line. As the guy said above, 9v is about right: you'll avoid overvolting your fans (you can overvolt fans with a wall brick; I did).

What? The disinformation police are on the way to beat you over the head with a nightstick. Sorry, I'm a EE, so I had to point it out.

 

[aigomorla]

As zap said, get a paper clip in on a green + black wire.
Then the psu will work via switch on the rear.

Which is funny, because zap gave me an old psu and i converted it into a power station just to power the fans on this:

Its my impluse drive on a sovereign class starship.

 

[Modelworks]

$2 + tax and problem solved
http://www.radioshack.com/product/in...LAID=107599355

attach to the yellow + black wires on the sata power connector.

 

[ehume]

What? The disinformation police are on the way to beat you over the head with a nightstick. Sorry, I'm a EE, so I had to point it out.

I don't care what theory says. My nominally 12v wall brick provided 17v to my fans, one at a time, measured with my multi-meter. When I plugged in more than one fan, the speed of previously connected fans went down, and the voltmeter said the voltage was down. I'm guessing that if I had provided the load the brick was designed for it would have given 12v.

I don't know why this was so. I just observed it. It screwed up my opinions on a number of fans until I learned how to start my psu without a mb.

 

[Modelworks]

I don't know why this was so. I just observed it. It screwed up my opinions on a number of fans until I learned how to start my psu without a mb.

It is because their are currently a couple different type of wall adapters.
AC only- inside is a transformer converting 120vac to something like 9vac
AC -- DC ---> above + diodes and a capacitor to convert the 9vac to 12VDC
AC --DC ---regulator---> above + regulator to make sure output is no more than 12VDC
AC--SMP----> no transformer but switching supply inside casing like in a pc.

Easiest way to tell the difference is weight. If it is really heavy it is a transformer and the output will likely vary with the load. The regulation is usually not done in the adapter but in the device so keeping it at exactly 12VDC wasn't something the manufacturer cared about.

Lighter weight adapters are smp like in a pc. Copper is expensive right now and transformers use miles of wire, so most new supplies are smp.

 

[ehume]

It is because their are currently a couple different type of wall adapters.
AC only- inside is a transformer converting 120vac to something like 9vac
AC -- DC ---> above + diodes and a capacitor to convert the 9vac to 12VDC
AC --DC ---regulator---> above + regulator to make sure output is no more than 12VDC
AC--SMP----> no transformer but switching supply inside casing like in a pc.

Easiest way to tell the difference is weight. If it is really heavy it is a transformer and the output will likely vary with the load. The regulation is usually not done in the adapter but in the device so keeping it at exactly 12VDC wasn't something the manufacturer cared about.

Lighter weight adapters are smp like in a pc. Copper is expensive right now and transformers use miles of wire, so most new supplies are smp.

Thank you. The wall brick in question is rather old and quite heavy.

 

[gorobei]

Won't the USB cable provide 5v?

5volts is enough for most fans, i just did a 5/7 volt pin mod on a molex extension so i could tune down some of the noise on the 120, 140, & 230mm fans in my TT element S.

plus there are plenty of videos on youtube showing it working fine off of usb power.