Three pin fan onto four pin header

Old Geezer · 8 Jan 2020 at 13:00

Nooby question, I know you can fit a three pin fan onto a MB four pin header, but how do I know which end to fit it to? TIA

ubern00b · 8 Jan 2020 at 13:06

Both the motherboard header and the fan molex are keyed so it can only fit in one way.

Old Geezer · 8 Jan 2020 at 13:59

Thank you, very helpful. Excellent photo by the way.

andy_mk3 · 8 Jan 2020 at 14:02

Yep as above. And it will work perfectly fine, you just obviously don't have the pwm control. It'll be voltage control only.

Old Geezer · 8 Jan 2020 at 14:16

Yes, that's correct. My new case (Fractal Design Focus G) has two 3pin fans fitted, and my MB (Asrock B450B Pro4) has 4 x 4pin headers.
This is my first build ever.

doyll · 8 Jan 2020 at 16:55

Old Geezer said:
Nooby question, I know you can fit a three pin fan onto a MB four pin header, but how do I know which end to fit it to? TIA

While you can easily plug a 3-pin fan into a 4-pin fan header, that does not mean 4-pin header is PWM or variable voltage. Often 4-pin headers are variable voltage, but if it is really a PWM header then pin-2 has 12v constant power meaning 3-pin fan will always be running at full speed. But also just about as often 4-pin fan headers on newer motherboards can be set to PWM or variable voltage in Bios.

Plug it in and see. You might be lucky and your 4-pin header is really a 3-pin variable voltage header with pin-2 being variable voltage, not constant 12v as it would be as 4-pin PWM fan headers are.