CPU_OPT fan spins too fast

Toggle sidebar Toggle sidebar
S

sasklo

Prominent
Jul 29, 2017
6
0
510
I have a Hyper 212X cooler with two fans attached to an ASUS Prime Z270-A . The front fan is connected to CPU_FAN and the back fan to CPU_OPT. I'm using ASUS AI Suite to manage the fan speeds and I'm noticing that CPU_OPT fan is spinning at almost twice the speed of the main CPU fan. The main fan is spinning at around 800 rpm and the CPU_OPT is spinning at 1500 rpm. I don't know if having differing CPU fan speeds will be detrimental to cooling performance, but both fans are rated to only 1000 rpm and the CPU_OPT fan is running way above that. Manually setting the rpm of the fans to 1000 rpm in AI Suite also doesn't work. If I do that, the main fan runs at 1000 rpm while the CPU_OPT runs at 1900 rpm.

How can I get both fans to run at the same speed? I didn't get this problem when I used this cooler with my old ASUS H97-Pro Gamer motherboard. Thanks!
 
Solution
P
Well, you certainly have different fans. That makes me question your statement that BOTH fan are rated for 1000 rpm. Certainly the one you linked above is a max 1000 rpm 3-pin model.

The difference in pins of the two fans IS significant. For any 3-pin fan the header's Mode should be set to DC Mode. (A 3-pin fan connected to a header using PWM Mode will always run full speed, which is what you are seeing now.) For any 4-pin fan, that setting can work but you are much better to set its header to PWM Mode. From what I see in your mobo manual Section 3.2.3 QFan Control, you can set those options for those two headers differently - there is NO need for them to match. So, set the CPU_FAN to which the 3-pin fan is connected to DC, and set the...
Sort by date Sort by votes
S

sasklo

Prominent
Jul 29, 2017
6
0
510


It's a bit hard to tell since they're right next to each other, but one of them is definitely hitting close to 2000 rpm based on how loud it is. This is with the fan speeds manually set to 1000 rpm.
 
Upvote 0 Downvote
P

Paperdoc

Polypheme
Ambassador
Oct 19, 2006
11,295
1,044
69,340
Some things don't make sense here. The Hyper212X cooler system is supplied normally with a single fan. You have two. So that prompts the question: are both fans the same? If they are different, give us the maker and model numbers of each.

Next, you say both fans are rated for 1000 rpm, but one of them is running 1500 rpm and you have seen it as high as 2000. Well, a fan designed for a max 1000 rpm will do that if sent a full 12 VDC signal, and will NOT go any faster. So, either the fan speed readings are wrong, or the info on the fan specs are wrong. We're back to the identity of the two fans. I am assuming when you quote fan speeds you are reading those in the AISuite software, correct? Or, are you using some other utility?

The mobo manual does not say anything about this next idea, but it is a feature on some ASUS mobos, so check this detail. You are using two fan headers for the two fans. Each can be configured separately in BIOS Setup - see QFan Control on p 3-7. Among the options for fan headers, SOME ASUS mobos allow you to specify which temperature sensor is used for reference. IF that choice is available to you for these two headers, ensure that the both are configured to use the sensor inside the CPU chip, and not another elsewhere on the mobo.

While you're checking that idea, compare the other configuration settings for these two headers. They ought to be the same.
 
Upvote 0 Downvote
S

sasklo

Prominent
Jul 29, 2017
6
0
510


I'm not 100% sure since it's a few years old, but I think the fan I have is this one:
https://www.newegg.com/Product/Product.aspx?Item=N82E16835106230

The first fan is the one that comes with the cooler, and yes I'm using AI Suite to monitor the fans.

I just remembered that the second fan has 4 pins and the first has only 3 so that might have something to do with it. I went into Q-fan like you suggested and tried switching the CPU fan from DC to PWM. The 3-pin fan is now stuck at 1000 rpm but at least I can control the second fan to match it. I'm guessing there's no way to change the mode of the two fans individually?
 
Upvote 0 Downvote
P

Paperdoc

Polypheme
Ambassador
Oct 19, 2006
11,295
1,044
69,340
Well, you certainly have different fans. That makes me question your statement that BOTH fan are rated for 1000 rpm. Certainly the one you linked above is a max 1000 rpm 3-pin model.

The difference in pins of the two fans IS significant. For any 3-pin fan the header's Mode should be set to DC Mode. (A 3-pin fan connected to a header using PWM Mode will always run full speed, which is what you are seeing now.) For any 4-pin fan, that setting can work but you are much better to set its header to PWM Mode. From what I see in your mobo manual Section 3.2.3 QFan Control, you can set those options for those two headers differently - there is NO need for them to match. So, set the CPU_FAN to which the 3-pin fan is connected to DC, and set the CPU_OPT header for the 4-pin fan to PWM. That should put both under automatic control. However, since the two fans are different, do NOT expect them to deliver the same speeds. Given a signal to each fan to run at, say, 80% of max, they each will do very roughly that. BUT the "max" of the 4-pin fan clearly is not 1000 rpm, so it will not run at 800 rpm like the 3-pin fan does given such a control signal.

There's another factor here that you are not taking into account. On a push / pull arrangement of fans on a heatsink, the aim is to have each fan deliver approximately the same AIR FLOW given identical control signals. You seem to assume that identical SPEEDS will do this, and that is not so. In fact, predicting air flow from speed can be done only roughly for each fan design, and trying to match air floe from two DIFFERENT fans over a range of input control signals is really impossible.
 
Upvote 0 Downvote
Solution
You must log in or register to reply here.

TRENDING THREADS

Latest posts

Share this page

COMPANY
RESOURCES
FOLLOW
Top Bottom