[SOLVED] Corsair SP 120 Fans wont change in BIOS

Nov 3, 2020
8
0
10
0
Have 3x SP 120 fans installed, connected to my included PWM REPEATER from my Corsair 275Q case, and then onto the CPU_OPT port on my Gigabyte AORUS TRX40 AORUS PRO WIFI. When in the BIOS in the Smart Fan 5 section, FULL SPEED, SILENT etc don't respond. I'm a little confused as to why it won't change settings, as I was hoping to change it to silent / quiet mode. Maybe I'm missing something? Help! Thanks
 

Paperdoc

Glorious
Ambassador
The problem is that these are 3-pin fans. When you plug a 3-pin fan into a mobo header that is using the new PWM Mode to control its fan's speed, that fan can only run full speed always. That is because the new PWM design for 4-pin fans supplies the fan with a constant 12 VDC power line on Pin #2, and then adds the PWM control signal on Pin #4 that the FAN must use (with its special chip) to control its speed. The older 3-pin fan's speed requires instead that the VOLTAGE supplied to it on Pin #2 be VARIED to change fan speed. That PWM Repeater unit that came with the case can only work with 4-pin fans. There are very few fan Hubs that can work with 3-pin fans, but if you need one, we can tell you where to get.

However, all is not lost. Your mobo has two headers designed for case cooling fans, called SYS_FAN1 and 2. See your manual p. 34 under the heading Fan/Pump Control Mode. Each of those headers CAN be set here to use the Voltage Mode, rather than PWM Mode. THIS is how you CAN control the speed of 3-pin fans. BUT you need a different and simpler device to connect several fans (say, three) to a single mobo header. A header can supply up to 1.0 A to its total load. In the SP120 line, the Corsair site says there are three varieties they sell: iCue SP120 RGB Pro Performance, SP120 RGB LED High Performance, and Air Series Sp120 LED in either Red or Green. Each of these shows specs of max current draw of 0.30 A per fan or less. IF you have a fan with NO lights at all in it, it will have even less current draw. So 3 of these together on one header is OK at a max 0.9 A current. To achieve that, you need a SPLITTER not a Hub, and ideally with 3 output "arms". A SPLITTER has one input "arm" with a female connector to plug into a mono fan header, and two or more outputs "arms" with male pins to plug your fans into. It may look like a collection or wiring "arms" or a small circuit board. A HUB is a different device that has those "arms" or connectors, but also a third "arm" that must plug into a power output from the PSU. That is what the Corsair PWM Repeater is, although you may find it hard to trace down all its connections. So don't get another HUB. An example of a Splitter is

https://www.amazon.com/Splitter-Computer-Extension-Converter-TeamProfitcom/dp/B07F8LV1BY/ref=sr_1_4?dchild=1&keywords=fan+splitter&qid=1604457067&sr=8-4

That's a twin-pack of 3-output Splitters. Just a note of explanation. Whether you use a Splitter or a Hub, the mobo host header can only accept the speed signal sent back from ONE fan, so the Splitter will only send it one fan's speed signal. If you look at the photos closely, you will see that, among the three output connecotrs, only one has all 4 pins, and the others are missing Pin #3. That is how the Splitter sends back the speed of ONE fan from its Pin #3 signal. And yes, these 4-pin Splitters WILL work with 3-pin fans; when you plug your fan in, it just won't use Pin #4.
 

Paperdoc

Glorious
Ambassador
The problem is that these are 3-pin fans. When you plug a 3-pin fan into a mobo header that is using the new PWM Mode to control its fan's speed, that fan can only run full speed always. That is because the new PWM design for 4-pin fans supplies the fan with a constant 12 VDC power line on Pin #2, and then adds the PWM control signal on Pin #4 that the FAN must use (with its special chip) to control its speed. The older 3-pin fan's speed requires instead that the VOLTAGE supplied to it on Pin #2 be VARIED to change fan speed. That PWM Repeater unit that came with the case can only work with 4-pin fans. There are very few fan Hubs that can work with 3-pin fans, but if you need one, we can tell you where to get.

However, all is not lost. Your mobo has two headers designed for case cooling fans, called SYS_FAN1 and 2. See your manual p. 34 under the heading Fan/Pump Control Mode. Each of those headers CAN be set here to use the Voltage Mode, rather than PWM Mode. THIS is how you CAN control the speed of 3-pin fans. BUT you need a different and simpler device to connect several fans (say, three) to a single mobo header. A header can supply up to 1.0 A to its total load. In the SP120 line, the Corsair site says there are three varieties they sell: iCue SP120 RGB Pro Performance, SP120 RGB LED High Performance, and Air Series Sp120 LED in either Red or Green. Each of these shows specs of max current draw of 0.30 A per fan or less. IF you have a fan with NO lights at all in it, it will have even less current draw. So 3 of these together on one header is OK at a max 0.9 A current. To achieve that, you need a SPLITTER not a Hub, and ideally with 3 output "arms". A SPLITTER has one input "arm" with a female connector to plug into a mono fan header, and two or more outputs "arms" with male pins to plug your fans into. It may look like a collection or wiring "arms" or a small circuit board. A HUB is a different device that has those "arms" or connectors, but also a third "arm" that must plug into a power output from the PSU. That is what the Corsair PWM Repeater is, although you may find it hard to trace down all its connections. So don't get another HUB. An example of a Splitter is

https://www.amazon.com/Splitter-Computer-Extension-Converter-TeamProfitcom/dp/B07F8LV1BY/ref=sr_1_4?dchild=1&keywords=fan+splitter&qid=1604457067&sr=8-4

That's a twin-pack of 3-output Splitters. Just a note of explanation. Whether you use a Splitter or a Hub, the mobo host header can only accept the speed signal sent back from ONE fan, so the Splitter will only send it one fan's speed signal. If you look at the photos closely, you will see that, among the three output connecotrs, only one has all 4 pins, and the others are missing Pin #3. That is how the Splitter sends back the speed of ONE fan from its Pin #3 signal. And yes, these 4-pin Splitters WILL work with 3-pin fans; when you plug your fan in, it just won't use Pin #4.
 

ASK THE COMMUNITY

TRENDING THREADS