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Rampage IV Black Edition PWM Control???

Level 10
Hello all,

I have been away from the forum for a while because I have been constructing my new water loop, which I finally finished today. I have run into a problem regarding the pwm control capability of the fan headers on the board. Here are the devices that i wish to control and here is the problem that i have run into:

My loop includes 2x 480 rads, each with four pwm fans. In order to control said fans (Corsair sp120's), I purchased a swiftech 8-way pwm splitter -- a device that includes an auxiliary SATA connector to supplement the boards limitation of 1A per fan header. If I plug all of the fans into the splitter and then connect the pwm cable to the cpu fan header on the board I am able to adjust the speed via pwm functionality. However, I am unable to control the speed of the eight fans from any of the other fan headers, as fan xpert2 simply fails to detect the fans as controllable. After doing a little reading and looking more closely at the manual, I noticed that although the chassis and opt fan headers are 4-pin, they are not pwm capable. Quite frankly I find this to be both misleading and a strange limitation to impose on such an expensive board... but that's irrelevant. According to the specs in the manual, only two fan headers have the requisite pwm contol signal: cpu fan & cpu opt. Now, I would be more than content with just using the cpu fan header in order to control the fans, but I have another device(s) that I want to control with pwm: 2x mcp35x pwm version pumps.

This is where I run into problems, as I am faced with the frustrating option of controlling either the pumps via pwm (and thereby running all fans on full) or vice versa. Obviously I am choosing to control the fans as opposed to the pumps, but I would really like to be able to utilize the pwm functionality of the pumps... I bought these models for a reason.

OK, I have two questions:

Since I must run my fans from the cpu fan header in order to control their speed via pwm, that leaves only one other pwm (not voltage regulation) header available: the cpu opt fan header. The problem is that although the pumps seem to run at variable speed when I connect them (with a 2-way pwm splitter) to this header, there is no way to choose a profile or set a custom curve or set rpm (etc...) from the BIOS or the fan xpert2 utility. Does anyone know how I can use the cpu opt fan header and actually control the device(s) connected to it??? I am beginning to wonder if this header is just an extension of the main cpu fan header, which would mean its setting would be aligned with that of the aforementioned fans. If this is the case, then that is a no-go, because I am not about to limit my pumps to 2500rpm when they should run around that speed at their lowest setting.

If my suspicions are correct, and their is no option to have two unique pwm control signals sent from the board, can anyone recommend an alternative. I am shocked by the lack of genuine pwm control devices on the market... virually all of them seem to control devices via voltage regulation, which makes one wonder why they call the pwm controllers in the first place. The only option that I can find is the aquaero xt or pro (not sure about lt), but in addition to eating up a front bay (none of which are available), these controllers are ludicrously expensive (~275$), and I really only need one pwm header to control the pumps. Can anyone recommend a cheaper option... preferably an internal or pci slot pwm controller that can be manipulated either manually (at back of case with a knob or something) or with software (via a usb connection)?

I know that this has been somewhat wordy, and I hope that I have explained my issue clearly. Any help would be greatly appreciated, as I will be truly pissed off if I have to shell out a couple hundred dollars and remove my ROG OC Panel from my front bay in order to control two pumps that ought to (at least in my opinion) be controllable via the MB headers themselves. I mean, what does 450 dollars buy if not a board that has pwm capablity on ALL headers!!! (Sorry, just getting frustrated as I type:mad:).

Thanks again for any suggestions,


Level 13
Hi Carson,

You are correct, CPU_OPT is tied to the CPU-FAN header for control. It cannot be controlled as a separate entity.


Not applicable
Raja@ASUS wrote:
Hi Carson,

You are correct, CPU_OPT is tied to the CPU-FAN header for control. It cannot be controlled as a separate entity.


Hi Raja & Carson,

I have the same problem here -> I have 2 EKWB PWM D5 pumps and a bunch of PWM radiator/case fans (4pin). Based on your discussion above, it seems to me that there is no way to separately regulate the speed of the pump and the speed of the fans at the same time. I have several questions, as follows:

Q: If I connect 'Fan+Pump to PWM splitter (e.g. Swiftech 8W-PWM-SPL)', and 'PWM Spliiter to CPU header', everything will run at the same speed?
Q: In that case, an acceptable speed for the pump might not be an acceptable speed for the fan right?
Q: Does the CPU header only monitors the CPU temperature?
Q: Can GPU temps be monitored and have fan RPMs adjust accordingly to the temps?
Q: If so, if my CPU runs at acceptable temperature resulting in fans&pumps running slow, but at the same time my graphic cards run hot, wouldn't it detriment my graphic performance (potentially burning them out)?
Q: Is there a workaround to this? (e.g. ASUS Fan Xpert 2)?
Q: Based on my understanding, ASUS Fan Xpert controls voltages (power), but true PWM controls signal while maintaining 12V power?
Q: If so, will controlling voltage via FAN Xpert damage my pumps and fans?

I am now thinking of running all fans at full speed (no PWM control), and just using the CPU header to control the pumps. If temp runs hot, water will run faster to be cooled by radiators. If temp runs low, water will run slow.
Q: Is this a plausible solution?

Need some expert help here, please.

Level 7
Why don't you guys get a fan controller like the Lamptron FC5 (I have one, it's great) and use a PWM profile settable fan header to control your pumps?