# Fan headers: CPU_FAN, SYS_FAN, PWR_FAN, NB_FAN, CHA_FAN, OPT_FAN



## Fractalogic (Jul 4, 2010)

Hi there!

I would like to discuss fan headers on PC motherboards. I currently have this GA-X38-DQ6 motherboard and it has the following fan headers.

CPU_FAN
SYS_FAN1
SYS_FAN2
PWR_FAN
NB_FAN

The CPU_FAN and SYS_FAN2 are 4-pin headers. The SYS_FAN1, PWR_FAN and NB_FAN are 3-pin headers. They have following pin configuration.


```
CPU_FAN/SYS_FAN2
----------------
Pin # Def
1     GND
2     +12V/Speed control
3     Sense
4     Speed control

SYS_FAN1/PWR_FAN
----------------
Pin # Def
1     GND
2     +12V
3     Sense

NB_FAN
------
Pin # Def
1     GND
2     +12V
3     NC
```
The CPU_FAN header is obviously intended to operate the CPU fan. But are there any rules about this? For example, would it work just as good if you were to connect the CPU fan to another available 4-pin header, such as the SYS_FAN2 on this particular motherboard? What fans do you connect to the remaining fan headers?

I have read from various sources that the PWR_FAN header was originally intended to be connected to the fan of the PSU. Is this true? This would have allowed for reading fan speed of the PSU fan. Although, I have never encountered a PSU that would allow this type of connection.

Some motherboards I've seen over the years had a CHA_FAN and a OPT_FAN header. Would this have been an equivalent to SYS_FAN and PWR_FAN? The CHA obviously stands for Chassis, and the OPT stands for Optional I guess.

This motherboard has the NB_FAN header. But it lacks the third wire (NC = no connection). Is there any good reason for this?


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## Oddba11 (May 13, 2011)

Depends on the motherboard. Some boards and/or the BIOS will not boot if a fan is not detected on the cpu header.

As for all of the other headers, it's typically recommended not to use them as it increases the load upon the motherboard power circuitry...which is better left only supplying quality power to the major board components.

If you need fan connectivity, use converters and attach them to power supply leads or better yet, use a fan controller.


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## leroys1000 (Aug 16, 2007)

The only one that really makes a difference is the cpu fan header
as it is usually failure monitored in the bios.
That can usually be disabled in the bios so the fan would run at
full speed without monitoring.
NB is the north bridge chipset fan header.
They usually use a small fan with a 2 pin connector.
Some motherboards use passive heatsinks and don't use that connection.
The 4 pin system fans are probably speed controlled according to system temperature.
The only power fan connectors I have ever seen were used in factory
built computer systems and did power the power supply fan.
Proprietary design so you would basically have to buy replacement
parts from the manufacturer.
Chassis fan is for a case fan of course and optional is
up to you.


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