I just finished building my custom PC, and I have two 80mm fans that have molex connectors, but not the three pin cables that connect to the motherboard (mine is a MSI H55M-E33). So, I just connect the fans directly to the PSU, and that works fine except that when I put the computer to sleep, the case fans continue to spin. I do have 2 fan ports on my motherboard, but I was wondering if there was a setting in BIOS or something that could shut the fans off even if they are connected to the PSU directly, or if I should just buy a cable to connect the fans to the motherboard.


  • If fans connect directly to the PSU, there will be no BIOS setting to disable them directly. Still, when computer is sleeping, I think (but could be wrong) that it should cut power to peripherals. On my PC, that's what happens, so no fan problems when sleeping for me. Check if you have correctly installed chipset drivers. It could be something related to them. – AndrejaKo Aug 18 '10 at 15:25
  • Take a look at this question: superuser.com/questions/82190/… It seems that if you can switch BIOS settings for sleep from S1 power state to S3 power state, fans should turn off. – AndrejaKo Aug 18 '10 at 18:06

If you want the fans to sleep with the board, plug them in with the board. If you want them to run even when the CPU sleeps, plug them into the PSU. That's why you have different connectors.

Note: You can plug two pin cables into a three pin slot. All you have to do is to disable the fan monitoring since the board will notice "oh, there is a fan that's stuck".

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  • That's what I figured. Is there an easy way to plug the molex connector into the mobo or should I buy a cable? – Brian515 Aug 18 '10 at 16:07
  • @Brian515 You can modify molex connector to be connected to motherboard, but I'd recommend against it. It's simply too much work and too big risk to replace a cheap adapter. It is much easier to buy a converter cable for the fan. – AndrejaKo Aug 18 '10 at 18:04
  • @Brian515: Since you ask, there probably isn't. With all the fans I had so far, I could simply plug the two-pin female cable onto the three-pin male on the board. The third pin will be tight or bent just a little. If you get it wrong, the fan won't work but it won't short-circuit either. – Aaron Digulla Aug 19 '10 at 7:12

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