![]() Plug a 4-pin fan into a 3-pin header and it gets no PWM signal so its chip cannot modify current flow. Plug a 3-pin fan into a 4-pin header and it will always run full speed because it gets a fixed 12 VDC from Pin #2, and no PWM signal from pin #4 that it cannot use anyway! You DO get good cooling but no speed control. Connect those fans each to the matching mobo fan headers that use their correct control signals, and they all work. It has a special chip that uses that PWM signal to modify the flow of current from that 12 VDC supply line though the windings to control speed. The new 4-pin fans are supposed to receive from Pin #2 a constant 12 VDC supply, plus the new PWM signal from Pin #4. Older fan have 3 pins and the ONLY way to control their speed is by varying the Voltage supplied to the fan on Pin #2 - from 12 VDC for full speed down to about 5 VDC for slowest speed without stalling. 14 can be confusing.įirst, some quick things about fans. Moreover the labels used in the manual on p. ![]() That mobo's fan control features are from early in the introduction of 4-pin fans and do not include items common now. *** I am unable to upload a picture from my google drive because idk. Any questions, I will answer as soon as I can! Sys_fan2/pwr_fan are ground, +12v, sense. Cpu_fan is same but switching 'reserve' pin for a speed control pin.(I am using bios voltage setting to control cpu fan speed). The system fan 1 pins are as follows: pin 1 ground, pin 2 +12v/speed control, pin 3 sense, pin 4 reserve. Can anyone explain this to me? Is there anyway I can control the fan speed without buying a new 3 pin fan?Īre current 4-pin fans not compatible with my mobo's 4-pin sys_fan1 header? There's no option to select voltage control mode for the sys_fan1 like there is for my cpu_fan. Well, what does that mean? It's like an only backwards compatible 4 pin for DC fans with no PWM signal. I took a look at my mobo manual, I will upload a photo, but from what I am seeing the 4th pin isn't a PWM speed control pin, it's just a 'reserve'. Why is my 4-pin sys_fan1 stuck at around 700-800 rpm? Admittedly, my other fans are DC 3-pin, but they adjust according to system temps. No matter what setting I choose, the system fan 1 never runs higher than 1000rpm, which is odd because every other fan is running over 1000 rpm. I have tried 2 different 4-pin fans, and I have also tried every configuration in the BIOS auto/silent/manual with.
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