SPCR

A while ago I made an adapter cable where the tacho and PWM leads connects to the Cpu Fan header and the power leads("+"/"0v") connects to a normal case fan header. The Cpu header outputs a PWM signal, and the case fan header outputs a variable voltage, this controls the speed of the radiator fans(water cooled system).

Tinkered a bit with the fan curves in bios and ended up doing a graph. With only PWM I can get the speed down to ~745rpm and with only variable voltage I can get the speed down to ~315rpm(reasonable reliable), with both the speed gets down to 235rpm.

Welcome to SPCR.

Fun tinkering. What's the fan make/model?

Does the fan reliably start up at the 235rpm point or do you have to start it at a higher point and then slow it down?

It's EK-Vardar F3-120 fans.

The motherboard runs all fans at full speed for about a second during boot before they slow down. If I manually stop a fan after boot it won't start again at that low setting.