ASUS P8Z68-V Pro CHA_FAN_OPT new fan header?

[techSlave]

Whats the intended use of ASUS P8Z68-V Pro's new CPU_FAN_OPT fan header?

CPU_FAN_OPT is a 4-pin PWM fan header connector next to CPU_FAN that wasn't on the P8P67 models that I know of. The manual lists it in several places, but doesn't include supported for it in the ASUS FAN Xpert feature (pg 2-26). But then it's listed as a monitored fan in the BIOS (pg. 3-25). (?)

I'm using a Corsair H70 with two Arctic F12 fans in push/pull configuration through the radiator. I intended to use CPU_FAN with the PWM sharing feature as I did on the P8P67, but that only monitors one of the fans and since one is slaved to the other they ramp together.

If this fan is actually controllable via fan-Xpert, could I control the push/pull fans separately? For example, put the pull fan on CPU_FAN, the push fan on CPU_FAN_OPT, then set the push fan to 0-RPM up to 50C, have the pull fan on at some level all the time (of course) and ramp them up from there? The advantage would be one less fan spinning at low load but good flow at max load.

 

[wongnog]

I noticed this header too and initially plugged one of my CPU fans to CPU_FAN and the other to CPU_FAN_OPT. Then I re-read the manual, I think CPU_FAN_OPT is a monitored fan in BIOS but it is not a controllable fan by FAN Xpert. The only ones that are controllable are CPU_FAN, CHA_FAN1 and CHA_FAN2. I ended up connecting my CPU fans to CPU_FAN and CHA_FAN2, and my rear chassis fan to CHA_FAN1. Seems a bit dumb but I think it works for me.

 

[techSlave]

I noticed this header too and initially plugged one of my CPU fans to CPU_FAN and the other to CPU_FAN_OPT. Then I re-read the manual, I think CPU_FAN_OPT is a monitored fan in BIOS but it is not a controllable fan by FAN Xpert. The only ones that are controllable are CPU_FAN, CHA_FAN1 and CHA_FAN2. I ended up connecting my CPU fans to CPU_FAN and CHA_FAN2, and my rear chassis fan to CHA_FAN1. Seems a bit dumb but I think it works for me.

Yeah, to answer my own question, you're right. Now that the system is installed it's obvious that there is support for monitoring but not controlling CPU_FAN_OPT either BIOS and in FanXpert.

Thinking about it a little more, think it might not be advisable to put one of the CPU fans on a CHA_FAN circuit. Reason being CPU temps usually jump more quickly than ambient temps and I would think it would be better for the CPU fans react more quickly than slowly. Also, I've read it's not advisable to run the H70 in a one fan situation; I don't know what the verdict on a one and a half setup would be though.

For this reason I've gone back to slaving the fans together until support for controlling CPU_FAN_OPT comes out in a BIOS update.