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Fan header questions?

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Rich_T

Member
Joined
Aug 16, 2002
Location
U.K
Hey all,

I always thought that the fan headers were used to give power to the fans and also vary the rpm to give correct cooling for the cpu. If that is true then whats the point of putting on a fan with a sensor (i.e Smart fan II)?

Also I know that some fans are to powerful to put on the fan headers and needs to be connencted directly onto the PSU, is the cable to do this called a 3 to 4 adapter cable?

Thanks

Rich_T
 

Paxmax

Member
Joined
May 8, 2002
Most motherboards just use the header to power the fan, and MONITOR the speed. A few can probably also adjust the speed.

It would be very dangerous to combine bios controlled speed + external control by thermistors. You'll risk underpowering the fan and the second controlunit, and ultimately fry your cpu.

Use only one controller at a time! :) /Paxmax
 

lazerin

Member
Joined
Jul 13, 2002
Location
Australia
The header is a 3 pin molex connector usually. The three pins are ground, 12V, and rpm. Some fans might not have the rpm lead and therefore you cannot monitor the rpm of the fan.

The 3 pin fan headers on your motherboard provide power, ground the fan and monitor the rpm if its available. Regarding controlling the rpm via the headers on the mobo, the PLL IC chip that controls the system bus (FSB) sometimes incorporate a fan controller in there. However, the techonolgy used is based on varying the voltage to the fan headers. It uses a resistor that is built in on the mobo whoes purpose wasnt for this, so it is risky to use the PLL to control fan speed.

If you have a power hungry fan like the SmartFan II, you should use the included 3 to 4 pin molex adapter so that you can plug it straight into the PSU.

The sensor control the fan speed with a resistor that is on the fan itself, so it does no harm to other components.

Hope this helps
 
OP
Rich_T

Rich_T

Member
Joined
Aug 16, 2002
Location
U.K
I understand know, thankyou for your replys guys :)

Rich_T