Controlling the chassis fan speed on ASUS M5A78L-M/USB-3

Jan 23, 2019
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Hi, I have a 3 pin header called CHA_FAN on the mobo in which i have a 3 pin fan connected, no PWMs involved. This fan is going on 100% rpm all the time.
The Cool'n'quiet function in the BIOS only allows for the control of the CPU fan, not the chassis fan.
For some ASUS mobo's there is a Chassis Q-Fan control option in the BIOS just below the CPU fan control, does this mean my BIOS is too old and i should update or does it mean my mobo just doesn't support that function?
Also, according to some people, even 3 pin conectors should be able to control the fan speed through voltage control mode, but i was unable to find out if my motherboard supports this.
If possible I want to avoid buying a fan controller or adapter to lower the voltage. I have tried SpeedFan, but that didn't work.
Thank you for your time :)
 
Jan 23, 2019
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Do you mean ASUS Fan Xpert+ ? If yes, all that says is that my system is not supported by the software.
 
It appears you are quite right. The pinout labels for the CHA_FAN header on your mobo suggest its Pin #2 always supplies a full 12 VDC, and does no fan speed control. The only fan header that does speed control is the CPU_FAN header, and it appears that is only using the new PWM Mode, so that cannot control your 3-pin fan.

So you could go one of three ways.
1. Put up with it, and don't change anything.

2. IF you have only the single CPU cooler fan and one case ventilation fan, you could replace the old 3-pin case fan with a 4-pin (PWM type) case fan. Also buy a simple SPLITTER like this

https://www.newegg.com/Product/Product.aspx?Item=N82E16812423160&Description=Coboc%20fan%20splitter&cm_re=Coboc_fan_splitter-_-12-423-160-_-Product

Look closely at the two male output connectors. One has all four pins in it, and you MUST use that one to connect your actual CPU cooler fan. That way the speed of that fan will be reported to the CPU_FAN header which monitors that signal carefully to check for fan failure. Use the other output (missing Pin #3) to plug in your new 4-pin case fan, and it will be speed-controlled also, although its actual speed will never be shown to you.

3. If you have many fans, you may not be able to connect them all to a single mobo fan header. Almost all such headers are limited to a max of 1.0 A current to all the fans connected to it. In that situation you need a fan HUB, which craws all power for its many fans from the PSU directly, and uses the PWM signal from one mobo fan header to set fan speeds. Now, almost all such devices can only control 4-pin fans, but there is one exception which would suit you. The Phanteks PWM Hub works a lot like all the others, BUT instead it uses the PWM signal from the mobo header to create its own group of six 3-pin fan ports all using the older Voltage Control Mode and hence suitable for use with any mix of 3- and 4-pin fans.

In both those latter scenarios you get all your fans - CPU and case coolers - controlled based on the temperature sensor inside the CPU chip. In ideal circumstances, the case cooling fans are controlled instead by a sensor on the mobo. But you can't do that. However, there is a good correlation between heat generated inside the CPU by changing workload, and heat generated by devices all over the mobo and peripherals, also determined by that same workload.
 

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