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Three or four wire fans

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dgk

Member
Joined
Feb 2, 2001
Location
Delray Beach FL
I see that some fans are 3 pin and some are 4 pin and I'm confused. The 3 pin would fit the power/monitor connectors on the motherboard, but some fans need 4 pins for more power, apparently. That would seem to use the standard 4 pin connectors used by the other peripherals, such as the drives. Then how do those fans get monitored? Or maybe they just don't. Do I have this right?

Also, I have a few 60mm fans from old power supplies I just trashed (well, recycled). They just have a red and black wire. Can I hook them to the red wire and one of the black wires on a standard 4 wire connector? Or the yellow and a black? I have a few cases that could use an extra fan.
 

Rob Cork

Senior Member
Joined
Dec 17, 2000
Location
Woodcote, UK
The four pin power connectors you refer to are 'molex' connectors - used for hard drives, cd drives and fans. They supply +5V (red wire) and +12V (yellow wire), and have two ground wires - the black ones in the centre. The fans are 12V fans, and only use one of the grounds and the 12V wire. The only difference, as you said, between fans with 3 and 4 pin connectors is that some require more power. The 3 pin headers on the motherboard do supply 12V - what the fan needs - but at a lower current than the psu molex connectors. That's why big, power hungry fans (120mm and most 80mm) need to be connected to the psu, not the mobo.

Not all fans with 3 pin connectors have rpm monitoring - the ones that do have an extra wire in the centre (blue I think). It is possible to leave the connector plugged into the mobo with the blue wire sending its information to the mobo, but to cut the power wires and hook them up to a molex connector so the fan can get a higher current, and more power. It's not possible to monitor a fans rpm through only a molex connector - the fan has to have a third wire connected to a mobo fan header for monitoring.

If you want to hook those psu fans up, attach the fan's black wire to either of the black wires from the psu molex connector, and the red wire from the fan to the yellow wire from the molex connector (I know it's confusing, red on psu = 5V, red from fan = 12V). That'll give the fan the 12V it needs.