Fan control hell

fonsui · January 24, 2021

I have recently been upgrading my setup, and I've gotten to the fans now and it is giving me much grief. Hopefully the hivemind can offer some insight. I am working with a Gigabyte x99 UD5 board, a Fractal Design Nexus+ 2 fan hub, and a mix of 3- and 4-pin fans. I'll list the three issues below, and expound on each:

1) 3-pin fans in 4-pin headers not behaving as expected: A variety of old and new 3-pin fans, when connected to the 4-pin PWM headers on the mainboard, budge a teensy bit on power-up and I get no further action out of them. The very same fans when connected to a 3-pin connector (more on this in part 3) all power up and work just fine. I am connecting the fans to the correct 3 pins on the 4-pin connector by aligning with the guide, but I have also forced the connection the other way, just to ensure that I've covered all bases. Connecting 4-pin PWM fans to these headers works as expected, BIOS and operating system level software are able to monitor and control these fans without issue.

2) BIOS control vs. mainboard manufacturer Windows software vs. third-party Windows software: The system BIOS has fan curve configurations and other monitoring/alarm capabilities, but I cannot tell if these settings are left in place in the absence of operating system software and only replaced if such software is present, or if these settings are ignored/discarded by the operating system as soon as it boots. I am also unaware of how third-party fan control software will interact with the BIOS in place of or alongside the manufacturer software, or how it will interact with the manufacturer software as well. Example: I configure a fan curve and alarm/shutdown conditions in the BIOS, boot an operating system, configure the same settings with different values in my Gigabyte software. Which takes precedence? When? What happens if I then uninstall my Gigabyte software?

3) Fractal Nexus+ 2 fan hub behavior: My Fractal Design case came with a pre-installed Nexus+ 2 Fan Hub. This is equipped with a power input with a SATA power plug adapter, a 4-pin PWM input from the mainboard, and multiple 4-pin and 3-pin fan headers. When connecting a 3-pin fan to any of the fan headers, 3- or 4-pin, they spin up as normal, but even with the 4-pin input to the fan hub connected to a sys fan header on the mainboard, no RPM readings are available. When connecting a 4-pin fan to the 4-pin fan headers on the fan hub, with or without the 4-pin input connected to the mainboard, these fans exhibit the same behavior as 3-pin fans - they operate at full speed, and the mainboard sensor receives no data regardless of the fact that the 4-pin input on the fan hub is connected to the mainboard directly. I understand that monitoring multiple fans on a single header may not be practical, even if the fan hub had the capability of averaging the RPM readings together and reporting that as a single reading, but the presence of the 4-pin connector to the mainboard indicates that some sort of either sense or PWM function surely is available, otherwise what is its purpose? The fans do not spin up without the SATA power, do spin up without the 4-pin to the mainboard, do not report RPM, and do not respond to PWM.

I am hopeful that I can get some clarity on this issue and put it to bed; it's less about the setup being perfect at this point and more about me understanding what's going wrong.

narrdarr · January 24, 2021

1. you may need to tell the bios that 3 pin(DC) fan is connected to the specific header.

2. yes software will override the bios setting fan settings once booted to the OS.

3. the fun hub can be connected to any header. All fan connected to that hub will all operate at the same speed. some hubs have at least one connection where a fan(usually a PWM) need to connect to act as the sensor for the all the fans speed

GhostRoadieBL · January 24, 2021

is this the BIOS fan control screen you are using?

the bottom left has the control system for your fan headers. set it manually to PWM for 4 pin and your Nexus hub, voltage for the 3pin fans regardless of if the 3pin fans are plugged into 4 pin headers the motherboard will switch modes to the one you manually set. Typically this happens when set to auto but some fans don't read correctly.

from #1 symptom the 3pin fans are set to pwm and the fan control curve starts too low to get the motor to turn so it twitches and never starts.

for #2 the software will intercept and change the bios signal while windows is running, anything outside of windows or with the program not running (typically they also have a background process) the bios will still send the signal to the fan headers.

#4, specifically

27 minutes ago, fonsui said:

they operate at full speed, and the mainboard sensor receives no data regardless of the fact that the 4-pin input on the fan hub is connected to the mainboard directly

this sounds like the bios setting is on voltage control and the bios is sensing it as an aio pump which causes the hub to send full 12v to the fans attached and not return an rpm because the bios isn't looking for rpm while in voltage mode. if you only have 3 pin fans the hub will never display an rpm reading in the bios as there is no rpm return line (4th line on the fan connector) from the fans connected to the hub

There could be an issue with the hub if; without the hub's 4pin plugged into the motherboard 4pin AND the header set to pwm and still having the fans at 100%

after all this the first thing to do is manually set the headers to voltage control, if you can avoid it don't use the hub and uninstall fan control software so you can isolate just motherboard and bios to test the fans without other software messing with things.

fonsui · January 24, 2021

12 minutes ago, GhostRoadieBL said:

the bottom left has the control system for your fan headers. set it manually to PWM for 4 pin and your Nexus hub, voltage for the 3pin fans regardless of if the 3pin fans are plugged into 4 pin headers the motherboard will switch modes to the one you manually set. Typically this happens when set to auto but some fans don't read correctly.

I'm going to examine this the next time I get an opportunity, it seems like the key. Thanks!