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Is there a way to make an old pc power supply power over 16 fans? Answered

I have 4 radiators on my water cooling circuit and each one has 4 fans...16 fans total but i have no feasible way to power all of them... any ideas on how to make an old 230 W pc power supply power the fans?



8 years ago

The typical old PSU regulates based on the load on it's 5V rail. If you only hook fans up to the 12V rail the result could be that it falls below 12V. That might be ok if you don't need more RPM than the resultant voltage causes but otherwise you'd want to add a roughly 5 ohm, 10W power resistor between 5V and ground (result is 1 amp, 5W, even with a 50% margin on the power resistor you will need to heatsink it to a large piece of metal so it doesn't overheat and become damaged). The rest is obvious enough, you already mentioned grounding the PS-On green wire to turn the PSU on but I have a better solution, that you solder a jumper wire between this green wire and the green wire on your other PSU that powers the system, this way the fan PSU turns on automatically when the other PSU turns on, and off when it turns off. The last step is connecting a wire from the ground of one to the ground of the other (black wire).

just hook up all the fans in parallel, and hook up the - to the black wires and the + to the 12 volt wires, the color changes from manufacturer to manufactuer, sometimes it's yellow, sometimes orange, sometimes blue, etc. to turn on the power supply you have to short out the activate wire to ground. Usually it's green. On the power supply match up wire colors to voltages and use deduction. There's also a powergood wire, you don't need that. Look online for pinouts of your specific powersupply. Many people put dummy loads on, but I don't think that will be a problem with you because you have a good load. DO NOT run the powersupply without the fans attached. I'm assuming those are pc 12 volt fans, right?

yeah they're 12 volt fans... and i found a little plug that "hacks" (couldn't think of a better word) the power supply into turning on... i just want to make sure that it won't freak out when i put all 16 fans onto it... im almost positive that this isn't going to work too well...someone please give a me a good reason why this shouldn't be done? i need to know why not in order to know why...

. Most of the fans I can find laying around pull from ~1.5 W to a little less than 4 W . Most of them are rated at ~2 W. PSU are rated for total output and the fans only use one voltage, so you need to check how many W the PSU will put out at fan voltage. Divide the W by two for a ballpark figure on the number of fans you can run.