So the Cha_fan1 port on my board doesn't seem to support PWM functionality, even being a 4pin header. I've got a Cougar 120MM Vortex PWM on that header as case exhaust. Great fans, especially quiet when under 1500Rpm. Sadly though, that header is always running at about 1800Rpm, even when set for Silent mode in the bios. I've got a PWM splitter, and today I tried pairing this fan with my Xigmatek Dark Knight II's fan on the CPU header. But as soon as I connected the splitter & rebooted, both fans are now at 1900Rpm, where before it was 1200Rpm. Even without the Cougar hooked to it, simply adding the splitter ups the Rpm drastically. That header is already set for Silent so I can't adjust it down enough without getting into the shutdown warning speeds. Just curious if anyone knows why the splitter does this? And has there been any word from Asus anywhere on the lack of PWM to this fan port?
A cheap splitter will have no output filters, fans will run full speed or whatever max Amps is on the port shared/split with the fans. Why not just install ASUS Fan Xpert and have it control the fan ports? Using the BIOS should work, but the fan is controlled more on percentage cycle and it will vary with system temperature, using Fan Xpert will allow precise control, either a fixed fan speed or your own custom fan curve.
The reason why its happening is that PWM fan splitters run full 12V and its grabbed from the PSU, so no way of controlling it, its meant to be regulated by PWM signal, but when your headers is not a true PWM fan header then there is no PWM signal, so the fans simply run at the full 12V. You have some option 1) Run the PWM splitter from a PWM fan header, in most asus motherboards is the CPU_FAN. 2) Run each of the PWM fans on each header, while not ideal as some PWM fans dont like undervolting, some do work, so you should be able to control them via fanXpert, just not in all cases you can drop them as you can on PWM. 3) Get 3pin fans and run them to the CHA_FAN1, 2, 3 etc. Just chose properly fans that can undervolt well. If you wish to read more, check ASUS Z87-Deluxe fake 4-pin headers & other fan control info
The splitter IS on the CPU header. Both fans run great & throttle perfectly on that connection when they're on it by themselves. But adding the splitter is what's messing up the control. It's a Silverstone CPF01 if that means anything to anyone. The Chas_2 & _3 headers also seem to throttle well, keeping my Cougar PWM 140mm's at ~900Rpm when on 'Silent' mode, and ~1450Rpm when on 'Standard' mode. It's just the Chas_1 header that runs 100%. Previously, with my Reserator 3 paired with the Cougar 120, both fans ran 1300-1500Rpm. But now, just adding the splitter cranks the RPMs and that's what seems really odd to me. Small edit: Was more curious about all this than anything. I was just hoping the splitter could get the Cougar under 1500Rpm, as that seems to be the sweet spot for noise for my system. Right now the Cougar is the loudest fan in my case. Below 1500Rpm, the GPU fans take that title.
If it is on PWM header like CPU_FAN, then install AISuite/FanXpert and you should get full control of the fan, you can even design your own graph into how you want the fan to react tot he temperature. And about the splitter, if both are the same PWM fans, then in theory both should have the same speed under the same PWM % signal, with +-100rpms or so, depending on the variance of the production of the fans. Now if you want more control on pure bios on PWM fans, go with MSI next time, or AsRock, much better bios than Asus in terms of controlling the fans without software, but software side, Asus is much better than MSI or AsRock imo.
