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BobingAbout

4pin CPU Fan header

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i have recently bought a DFI LanParty NF590 SLI-M2R/G board. looks cool, havn't tried it yet though, still waiting on my RAM to be delivered.

 

there is a 4pin CPU fan header, the manual says the extra 4th pin is for speed control, but i can't find any other information about it anywhere. maybe i'm just not looking properly.

 

anyway, does anyone have any information on how i can attach a standard 3pin CPU Fan to this 4pin header.

 

note, i am an electronics engineer, and have been building and servicing computers for several years now. being an electronics engineer, i don't mind having to contruct something to modify my existing fan(its part of a full copper heatsink, so, i don't really want to replace it. it came with a manual speed control backplate, which contains a circuitboard, and potentiometer, maybe this can be adapted to work for me?).

 

anyway, what i am looking for is the technical specs on this 4th pin. what kind of voltages or signals does it output, what do the voltage levels or signals mean? from these 2 peices of information alone i can build a small circuit that will vary the speed of the CPU fan.

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don't get me wrong but are you sure, it's a silly question but is it a floppy power connecter cause i've never seen a 4 pin fan black earth red 12v and yellow speed maybe use an adapter for you cpu fan and run it direct from the psu

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don't get me wrong but are you sure, it's a silly question but is it a floppy power connecter cause i've never seen a 4 pin fan black earth red 12v and yellow speed maybe use an adapter for you cpu fan and run it direct from the psu

 

look at the layout of the mobo, it really does have a 4-pin CPU fan connector, he's not mistaken, yet I don't know what's the 4th pin for...

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its in the manual, tells you what the pinout is, but, since my fan is only a standard 3pin, the 4th pin isn't used.

pin1 is black gnd, pin2 is red power (12v), pin3 is yellow RPM sence, pin4 is called "Speed Control"

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Guest Dice

Correct, they don't need an adaopter. Not sure what's made them start making boards with the 4 pin connector for CPU fan. My gigabyte AM2 board had it as well as the Infinity in my sig.

 

The 4 pin header is shaped so that the 3 pin connector fits fine.

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I think it comes from Intel standard CPU fan, which requires the 4th pin to control its RPM accordingly. It's a legacy from P4 presHOTT days, but my AMD 3200+ Orleans stock fan only has 3 pins, yet the MoBo can control its RPM according to the CPU temp without the need for the 4th pin, so what gives ?

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I think it comes from Intel standard CPU fan, which requires the 4th pin to control its RPM accordingly. It's a legacy from P4 presHOTT days, but my AMD 3200+ Orleans stock fan only has 3 pins, yet the MoBo can control its RPM according to the CPU temp without the need for the 4th pin, so what gives ?

 

Newer P4 boards (in particular all LGA775 boards) have a 4pin CPU fan connector. The 4th pin is most probably a Pulse Width Modulated signal allowing the MB the controll the fan speed while still delivering a constant 12V output to the fan (i.e. lowering the fan speed when the CPU cools down at idle; thus reducing the noise produced by the sys).

 

Fan speed controll can be achieved with a 3pin fan by varying (reducing) the voltage on the 12V line. The problem with this is that DC motors (fans) require a minimum voltage to operate; thus the voltage/speed range at which the fan will work is limited.

PWM on the other hand is a digital approach where the speed is controlled by turning on/off the fan in rapid pulses; by adjusting (modulating) the width of the time on and time off pulses the speed can be accurately controlled and operate at speeds slower than those achievable by reducing the supply voltage.

 

The only thing is that I am unsure how many 4pin fans actually use the control signal. I had one HSF that always ran full speed (extreemely loud) and drove me crazy; as a result I've now installed H2O cooling and eliminated that fan from the system.

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