[SOLVED] My 2nd CPU fan spins up at start-up but stops moving after post. How do I get it working?

[Budgeteer_262]

I have a fin stack style cpu cooler which only came with one 140mm fan. I wanted a push-pull airflow configuration so I also mounted an AVC branded 140mm fan from an OEM machine on the other side of the cooler.

When I boot the system, the first cpu fan (which came with the cooler) spins normally however the AVC fan spins up temporarily and soon stops moving after post screen.

The system works fine aside from this fault. Technically, the AVC fan is plugged into a chassis fan but I don't know why it would stop moving entirely. The bios also doesn't recognise a fan installed in that header.

Any tips on getting the AVC fan to work would be appreciated.

Thanks

 

[vov4ik_il]

Heya,

You would have to manually set this header to follow CPU fan temp/rpm curve (or create it). This can usually be done in BIOS or using motherboard-dedicated configuration software.

 

[geofelt]

What is the make/model of your cpu cooler and motherboard?

Motherboard bios may have a fan profile section that does not start the avc header immediately.
I might add that a second fan is not likely to add much to the cooling capability.

 

[falcon291]

What is your mainboard? And where do you plug these fans?

 

[Budgeteer_262]

I’m using an asus b85m-e board with a cooler master hyper 412s cooler. It comes with 1 fan and because push pull config helps a bit, and I had a spare 140mm fan lying around I thought why not mount it.

I’ve now found the fan preset settings in the bios and that got the 2nd fan spinning. For some reason it also suddenly recognised it in the bios.

I plug the cooler master fan into the cpu fan header and the pen fan into the chassis ram header. There is one more unoccupied chassis header.

the cooler master fan that came with it has 3 pins and the oem one has 4 pins.
Now that the fans spin I’m trying to control the speeds of the fans to respond to temperature and operate at the same speed but speed fan software won’t work here.

Any software I can use to customise and synchronise fan behaviour for these fans?

Also, I know push pull only adds 5 degrees or so but I had the unused fan anyway so a free improvement can’t be bad.

 

[Paperdoc]

On that mobo (like most), the two CHA_FAN headers can only use the temperature sensor on the MOTHERBOARD to decide what speed to run their fans. For what you are trying to do, you need to arrange for the added second CPU cooling fan to use the SAME control signal as the main CPU cooling fan. This means you need a SPLITTER to connect both of those fans to that CPU_FAN header. Now, the two fans are different types - one 3-pin, one 4-pin - but that can still work because a 4-pin fan CAN be controlled by a header using the older Voltage Control Mode. In fact, since you appear to have speed control of the THREE-pin fan supplied with that cooler unit, we can surmise that older Mode is what the CPU_FAN header is using. When you get the FOUR-pin Splitter, connect the supplied THREE-pin fan to the one Splitter output connector that has ALL FOUR pins - this is the only one for these fans whose speed will be sent back to the header. Connect the added 4-pin fan to the second output (with one pin missing). You will NOT "see" the speed of that added fan anywhere, but it will vary its speed in line with the first fan according to CPU cooling needs.

 

[Budgeteer_262]

Thanks for clarifying.

To be clear, I have no software fan control beyond basic "turbo" fan pre-sets in the bios for any of the fans, including cpu fan.

Suppose I were to simply remove the 4pin plastic plug and just jam the wire heads in with the three pin header, would that work? (from a purely technical point of view)

Also, given that speed fan can't control my PC fans and that my mobo is too old to have an asus fan control software for it, am I stuck with bios fan control?

 

[Paperdoc]

Actually, the mobo manual does say you do have ability to control fan speeds both at the CPU_FAN and the CHA_FAN headers. I will note, however, that it also claims on p. 1-15 that only the CPU_FAN header can use ASUS FanXpert 4 for fan control. Since your query is about the fans connected to this header, we'll start there. Look at manual p. 2-33, item 2.7.4. Set CPU Q-Fan Control to Enabled. Set CPU Fan Speed Low Limit to 300 rpm for now. this is the limit that will trigger an on-screen warning of low CPU fan speed if it goes under the limit or stops. Set CPU Fan Profile to Standard so it will automatically adjust fan speed for you according to the temperature measured inside the CPU chip. Next come two pairs of settings for details of how this is done, Set CPU Upper Temperature to 65 C and CPU Max Duty cycle to 100%. This means that when your CPU temp reaches 65 C (or higher) the CPU fans will run full speed. Now set CPU Lower Temperature to 20 C and CPU Min Duty Cycle to 20%, This means when the CPU temp is 20 C or lower the fans will be told to run at 20% of max. At temperatures in between these two points the system will use a simple straight-line "graph" of what speed to run for what measured temp. Be a little cautious of the MINIMUM speed setting. If that is allowed to go too low, one or both fans on your CPU cooler may stall and fail to re-start until the temps go higher. You want to avoid having them stall ever, so adjust this setting until you know what DOES cause a stall, then raise it so stall does NOT happen at the very lowest temperatures when your system first starts up cold. In setting these last four items you have just created your simple "fan curve", and setting to Standard Profile will use that curve for automatic control of the fans on that header.

The following section of the manual says exactly the same adjustments are available for each of the CHA_FAN headers, even if the earlier note says that FanXpert4 does not work on those headers. So try them out for your case ventilation fans.

After you have made changes, use the Esc key back to the Main Menu, then click at upper right on the Exit Menu item - see p. 2-42. There choose Save Changes and Reset to save your new settings and reboot. You can come back and re-adjust them if you need to.

Good luck and thanks for Best Solution.

 

[Budgeteer_262]

I managed to connect the two fans to the one header and am able to control it through the software. Have also set the other fans to the neccesary presets.

However, because the two fans are different brands and probably spin at different rpm, i don't think the software control works. They sound just as loud regardless of what fan profile I set in FanXpert.

At this point i think i need to just play around with it or make a compromise.

Thanks for the help

 

[Paperdoc]

Since the two fans on your CPU cooler are of different designs, there is a detail you should check. The basis of this is that a THREE-pin fan connected to a header using the new 4-pin PWM Mode for control will always run at full speed, whereas a 4-pin fan's speed WILL be controlled in that scenario. So, start by setting the configuration of the CPU_FAN header as I said above - especially using the Standard Profile setting. That will have the header try to control the fans' speeds.

Start with your system cold after NOT running for a few hours. Now, open the case so you can observe the two fans carefully. Reboot and watch those two fans immediately. For each of them, the normal sequence is that they start up at full speed almost immediately, but after a few seconds as the boot process is nearly complete, they both should slow down to a low-speed setting suitable for a cold system. NOTE what the fan speed number is.

For the next test, reboot directly into BIOS Setup and go to the CPU_FAN header. Set the Profile to Turbo, back out and go through the Exit Menu to Save and Reset. Again, watch the two fans. This time they should start at full speed and stay that way at all times. NOTE the fan speed shown this time.

Next, reboot into BIOS Setup and change the CPU_FAN profile to Quiet, then back out and reboot. This time BOTH fans should start at full speed and the BOTH slow down a lot. Note the new Fan Speed.

If there is difficulty in deciding how fast the two fans are running, you can re-do this test series but with one fan (say, the added 4-pin fan) disconnected from the Splitter so that you can concentrate on only one connected fan. Then do it again with that one re-connected and the OTHER fan disconnected.

If all those tests show that BOTH fans change from fast so slow when they are supposed to, then your fan control system IS working. If they show that ONLY the 4-pin fan's speed changes but the 3-pin fan never gets to run slow, then we have an answer. Such behaviour would tell us that the header is using ONLY the PWM signal system and it can NOT change the speed of the 3-pin fan, no matter how you set the Profile for the header. The sound that one fan makes may deceive you into thinking that neither fan's speed is under control.

Report what you find back here. There are a few options for what to do next, including leaving it alone. We can discuss when we know what those tests show.

 

[Budgeteer_262]

The fans do indeed slow down after high speed during post and sound louder on the turbo setting.

Software fan control would've been nice but bios control is probably fine.

 

[Paperdoc]

Glad you got it to work as you like. Thanks for Best Solution.