[SOLVED] case sys fans questions

4 Pin headers are PWM.

As far as using CPU fan headers for case fans, don't, its better to keep them for the CPU Cooler fans and in some cases an AIO Pump although anymore there usually a pump header (which your board does have). If you need more then 4 system fans headers then buy a hub. But past 2 or 3 fans its usually more about looks then any actual performance.
Apr 25, 2019
I have a 3pin cpu fan though. So there is no way to control cpu fan speed?
I am not using cpu fan headers for case fans. I am trying to use case fan headers for cpu fans, since I have a 2-fanned cpu cooler, but my motherboard only has one cpu fan header.


3pin fans are analog, DC voltage controlled. There's 3 wires, a hot, ground and tach. The hot wire can be from 5v to 12v or 7v to 12v, depending on the fan. This equates to 40% or 60% to 100% duty cycle in bios. Basically a 1000rpm fan at idle speeds will spin at 400rpm or 600rpm depending on if it's a 5v low or 7v low. And then raise to 1000rpm at 100% (12v)

4pin (aftermarket style) are PWM. They have 4 wires. 12v hot, ground, pwm signal and tach. A PWM fan always is fed 12v, constant. The bios sends a signal by the signal wire that looks like Morse Code. This has the affect of turning the fan off/on. The longer the pause between bleeps, the slower the fan spins. A PWM fan at any value less than 100% is always in a state of trying to start. Because of this and a 12v constant, PWM fans go as low as 20% duty cycle, so a 1000rpm fan at idle speeds is only at @ 200rpm ±.

There's 1 fundamental difference between the cpu_fan header and sys_fan headers. The cpu_fan header is dedicated pwm. It will not control a 3pin DC fan. It's a constant 12vDC. The sys_fan headers are interchangeable, depending on how you set them in bios. If set for DC, the 4pin PWM fans will struggle, if set for PWM then a 3pin fan won't change speeds.

To use 2 fans on any header you'll need a splitter. A 2way pwm splitter has 2x sets of wires joined to 1 connector. 1 set has 4 wires, standard hot/ground/pwm/tach. The other set only has 3 wires, hot/ground/pwm. You only want 1 fan to report its speed to the motherboard, the pwm signal is sent to both, based on the 1 fan speed.
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Actually, in your mobo all the fan headers have 4 pins, BUT the system is designed for full flexibility. Within the BIOS Setup pages, for EACH of your headers you have an option to set it to use the older DC Mode of control (which uses only Pins 1 to 3), or the newer 4-pin PWM Mode. So you set this option according to the fan type you plug into that header.

Yes, there IS an important difference between two groups of headers on your mobo. The difference is in the TEMPERATURE sensor used to guide each header's automatic control of its fans. The CPU_FAN1 and PUMP_FAN1 headers will use only the sensor inside the CPU chip because they are designed for use in controlling cooling of that chip. The five SYS_FAN headers, on the other hand, all will use only a different sensor built into the motherboard, because they are designed to control temperature inside the case generally. So, be sure to use the correct header for each fan, depending on what that fan is cooling. (There are some mobos that allow you to choose which sensor is used for the SYS_FAN headers to provide you with greater flexibility in how they are used, but your mobo does not appear to have this feature.)