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Question about 3-pin pwr_fan connector

Last response: in Motherboards
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March 17, 2006 2:22:23 AM

Hi, I'm building a comp for the first time, and I've run into something weird. My ASUS mobo's manual says that I need to plug a 3-pin connector from my power supply to the pwr_fan connector, but I can't find such a 3-pin connector among my PSU's cables (Ultra Xfinity 500W).

Do some power supplies not have this 3 pin connector? Or maybe I should look harder among the mess of cables? Thanks!
March 17, 2006 2:36:49 AM

yeah Antec psu has one, but in the antec manual it says you don't need to plug it in for the psu to work.
a b ) Power supply
a b V Motherboard
March 18, 2006 11:44:17 AM

The 3 pin pwr_fan connectors on your mobo supply power TO your fans. They use 2 of the pins for that. The third pin is to monitor fan speed. Antec power supplies often have a connector with 3 pins but only one wire to supply the mobo with PSU fan speed info. NO power should ever be INPUT to the pwr_fan connectors. Run your system fans either from the power supply using 4 pin molex connectors or the pwr_fan 3 pin connectors on the mobo. Make sure that the CPU heatsink/fan 3 pin connector is plugged into the mobo and you should be good to go. You should not find a 3 pin 3 wire female fan connector in the power supply wiring bundle. The Asus manual must have a misprint.
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March 18, 2006 9:16:18 PM

Quote:
Antec power supplies often have a connector with 3 pins but only one wire to supply the mobo with PSU fan speed info.


False... mine has 2 wires.


Quote:

You should not find a 3 pin 3 wire female fan connector in the power supply wiring bundle. The Asus manual must have a misprint.


correct mine is a 3 pin 2 wire fan connector and this is used to monitor the speed of the internal intake fan through the motherboard BIOS or through monitoring software included with your motherboard.
July 1, 2009 5:47:51 PM

Newf said:
The 3 pin pwr_fan connectors on your mobo supply power TO your fans. They use 2 of the pins for that. The third pin is to monitor fan speed. Antec power supplies often have a connector with 3 pins but only one wire to supply the mobo with PSU fan speed info. NO power should ever be INPUT to the pwr_fan connectors. Run your system fans either from the power supply using 4 pin molex connectors or the pwr_fan 3 pin connectors on the mobo. Make sure that the CPU heatsink/fan 3 pin connector is plugged into the mobo and you should be good to go. You should not find a 3 pin 3 wire female fan connector in the power supply wiring bundle. The Asus manual must have a misprint.

I found this thread, and specifically this post, via Google.

I have been experiencing similar confusion as the OP. However, I think I also made a serious error...

What would be the likely outcome of unsuccessfully attempting to boot a system whilst having made the significant error emboldened in Newf's post, above?

Have I destroyed my system? Please help!
a b ) Power supply
a b V Motherboard
July 24, 2009 3:04:33 PM

The pwr_fan connector should only be used to plug in a 3-pin connector that is among the cables from the POWER SUPPLY. Unlike other fan connectors, it is NOT used to supply power to that fan. It is only to supply a signal to the mobo from the PSU internal fan to confirm that it actually is running. It's simply another way for the mobo BIOS to check that all the system cooling features are working. If you don't have such a connector coming out of the PSU, don't worry. You might check, though, whether the BIOS Setup screens have a way to tell the BIOS to ignore this non-existent signal; in fact, it may be set that way already by default.

The CPU cooler fan must be plugged into the mobo's CPU_fan pins. If you have a 4-pin mobo connector and a 3-pin fan cable, pay attention to what your manual says about which pins to use - there is usually only one way, anyway, with little opportunity for confusion. IF you have any case fans, they should be connected to the mobo's CHA_fan1 and CHA_fan2 sockets if possible; if not, they can be powered from the PSU's 4-pin Molex connectors. Hooking them to the mobo connectors, however, gives the mobo BIOS a signal to monitor for proper fan function, and MAY (depends on your mobo) allow the BIOS to actually control those case fan speeds. The link provided by Gamerhomie above shows a manual page for a mobo with these capabilities. Note that it specifically says that the speed control systems are only available for the CPU and case fan connectors, and NOT for the PSU fan. That PSU fan speed is only monitored, not controlled, by the BIOS. Also note in that manual page that, if you have case fans to connect, it often provides guidance about which fan to plug into to which connector - this is common, so read your manual!
November 4, 2009 1:51:08 PM

Hi!

I'm about to plug in a Air-Flow fan for my Dominator GT memories, and I wonder where to put the 3-pin?

I have an ASUS P5Q PRO motherboard, and it has 4 3-pin places; CPU_FAN, PWR_FAN, CHA_FAN1, CHA_FAN2. The CPU_FAN is taken and as I've read here I shouldn't use the PWR_FAN, so can I just put it in a CHA_FAN* place and i'm good to go?
!