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"Fake" 4-pin PWM fan header on motherboards

maybethisnamewillwork
By maybethisnamewillwork
in Cooling
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Posted

On my motherboard CPU_FAN is the only one that has true pwm control, I can run my Noctua NF-A15 fan with the advertised min. speed ~350rpm at 20%.
But CHA_FAN and PWR_FAN headers are "fake" 1Amp DC headers. and the NF-A15 runs min. ~650rpm at 35%. I can still control the fans precisely by each %, but the min. rpm is higher and it doesn't supply continuous +12V like real pwm would.


Real PWM header pin layout:
1st = GROUND
2nd = +12V
3rd = RPM SIGNAL
4th = PWM CONTROL

So what's the purpose of the 4th pin when it doesn't have pwm function?

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 dont know , my boards had these headers but also in bios the option to set that header to DC or PWM , it might be a PWM header , but set to DC in bios , making the fan just spin away at 100% 

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It's so that people don't mistakenly plug a 4 pin fan into the wrong 3 pins, or complain they can't use a 4 pin fan because it only has 3 pins.

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Because they can and it looks better to have 4pin headers.

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