Question PWM, DC, fan splitter.


Mar 15, 2021
I just added my second PWM splitter. So now I have 1 splitter connected to 2 fans (CHA1) and 1 splitter connected to 2 fans (CHA2).... What I did notice however, when booting into BIOS and going to Qfan control, is that the fans were speeding up to 1400... Not all of them... just the ones plugged into CHA1. I noticed that it was in PWM which was odd to me because the fans are PWM and they shouldnt be throttling to that high of an RPM. And it wasnt on turbo, manual, or full speed... Just standard speed. So I switched to DC (seeing as how CHA2 is in DC) and the fan speed came down to the same RPM as CHA2. Im just curious as to why it did that? Why would PWM be speeding up that much? I really dont know crap about PCs so maybe someone could give some insight. Im still reading into it but there are so many answers that it can be difficult to seperate what is accurate and innaccurate.


You have not told us exactly WHAT fans you have. IF they are 3-pin fans (only 3 holes in the female connector on their cables), they are Voltage Control fans (aka DC fans) and BOTH your fan headers should be set to Voltage Control Mode (aka DC Mode). IF they are 4-pin fans then both headers should be set to PWM Mode.

Also check this detail in EACH of your CHA_FAN headers. They may each have a choice of which TEMPERATURE sensor they use for guidance. Since these all are case ventilation fans, they should be using the temp sensor on the MOTHERBOARD, and NOT the one inside the CPU chip. Further, IF either of those headers has an option to set whether the device plugged in is a FAN or a PUMP, ensure it is set to FAN use.