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Can't Set CPU fan below 60% duty cycle

Level 8

I've just built a new PC using an Asus TUF Gaming Plus WiFi Z790 board and a Noctua NH-D14 cooler. The Noctua cooler has a Noctua  NF-P12 PWM fan and a Noctua NF-P14 PWM fan connected via a splitter cable to the CPU fan header. All works fine but in the BIOS I can't set a CPU fan duty cycle below 60% for the fan curve whereas I can for the other fans. 

Why is this - perhaps something to do with connecting the fans via a splitter cable?


Level 7

I'm using a splitter on my Noctua PWM fans too,  but they are the same fan,  works fine.   Have you tried hooking them up individually to the header and see if you can fully control them?  I'd test that,  then if there is one that is fully controlled, then make sure that one is on the controlling leg of the splitter cable.   it's one of them,  some times you have to figure out which one.

I've now connect the two Noctua CPU fans to separate fan connectors (CPU & CPU_OPT). I still can't set a duty cycle below 60%. I'm unsue this is by design or  bug.


Under Q-Fan have you tried Optimised All?

13900KS / 8000 CAS36 / ROG APEX Z790 / ROG TUF RTX 4090

Level 8

Thanks. I spotted my motherboard has a CPU_FAN and CPU-OPT fan header so I could connect each fan to a separate fan header for full control. These have Q Fan control but the manual mentions these connections have shared control without explaining what that means.

As above, the fan control for these two headers is synced. Meaning any adjustments made to behaviour either in Q-Fan or FanXpert will be mirrored on both headers.

13900KS / 8000 CAS36 / ROG APEX Z790 / ROG TUF RTX 4090

Level 9

Shared means shared , lol.

On most boards cpu fan and opt fan are shared. One fan setting or fan curve for both. 

Some fans cant go below certain rpm. It depends on the fan type. There is a calibration tool on qfan bios settings to establish the minimum rpm they can go.