Old PSU to power case fans?

Hello, 1rst post.

I have a lot of fans ( Cosmos S case) and some very hungry video cards. (295 GTXs in Quad SLI)

I would like to rig an old PSU to power all my non MB regulated fans. It would not be tied into the PC in any way, just to the fan chain through a single Molex.

I started to read the dual PSU thread and wonder if I can just do the test step at the begining to get the old PSU to start with it’s back switch? I also hope to be able to leave these fans running a bit after shut down to cool everything down.

Please Advise.

Hi and Welcome!

either you need an old AT (not ATX) PSU, or you have to modify an ATX PSU since ATX PSUs need a “power good” signal to startup.


Why not just pickup a 12VDC wallwart of sufficient amperage to handle the requirements of the fans?

I have a total of 3.98 amps of fans, would a 4 amp walwart work or should I go higher? Also how do I splice to the Molex (need wiring config, 2 grounds?)

So I did as advised, picked up a 12V 4 amp (5amp max) walwart and spliced the adaptor to a Molex connector. Very spiffy. Problem is it spins my fans at only 1/3rd the speed I need (sensor only connected fan controller for speed monitoring)

So do I just increase the amps?

Are all 4 fans connected in parallel with the power supply? What does the voltage measure at the output of the wallwart? If it’s less than the rated 12vdc the fans are trying to pull more amperage than available thus pulling down the voltage level.

[QUOTE=palburke;2297391]Why not just pickup a 12VDC wallwart of sufficient amperage to handle the requirements of the fans?[/QUOTE]
This is a great idea.
I wonder if it could be piped into a quality analog fan controller like this :

Prolly need more amp cushion…inherent resistance in the controller will eat a small amount, too.
Maybe something in this class would stand up better :

Another good source is www.12vadapters.com. They have a number of 12vdc “BRICKS” of many different amperages at very reasonable prices.

I used 12vadapters.com for my 1rst brick. I figure I need to try and match the Thermaltake Tough Power 1200w PSU’s amps so I’m going to try this:


Fans are all chained to one string Molex to Molex with power supplied at one end.