How do I turn on/off a case fan without unplugging it?

Jun 3, 2017
6
0
510
My case has a mounting for a fan on top that I only want to use when my system will be under full load. I have a fan header on the motherboard that can be dedicated to just that fan. It can't be a PWM fan. Is there any way to turn it on/off? I thought this would be very simple but even fan controllers don't seem to have this option. Can anyone help me out?
 
Solution
If you use a third-party fan controller, you do NOT get automatic control of that fan in any way. YOU will have total control of what the fan does, so you'll have to turn it on or off.

It is not clear whether you want that fan to go on at full speed whenever you want it running, or whether you want it to vary its speed according to temperatures, but just not run when your system is cool. So I'll give you two options. Now, because your mobo will send the fan a power supply of varying voltage, it would be hard to get it to run at full speed all the time, but I'll give you a suggestion at the end.

First, the hardware limits and capabilities. The fan you specified is a 4-pin PWM type fan. Look at its cable closely. I expect it has 4...

Paperdoc

Polypheme
Ambassador
"unless it is a PWM fan it cannot be controlled" is wrong. 3-pin fans CAN be controlled, but it requires the correct method to be used by the mobo fan header. Some fan headers can do this, some can't.

For a complete answer, post back with:
Exactly what fan are we talking about? Maker and model. I presume it has only 3 wires from it and a 3-pin female connector on the end of its cable. Right?

Exactly what mobo - maker and model number. With that we can look up its manual and determine what its headers can do.
 

skibo1219

Distinguished
Aug 7, 2010
108
0
18,710
What fan controller are you trying to use? a PCi slot fan controller can shutoff the fan or turn it way down to be extremely quiet. If you mean software controlled fan, you can try SpeedFan but afaik only the CPU headers are controllable since none of the other fan headers on 99% of the motherboards out there are true PWM.
 
Jun 3, 2017
6
0
510
I'm not using any fan controller since I can't find one that turns fans off. I've tried speedfan and I couldn't figure out how to turn off a fan. If someone can guarantee that it's possible with speedfan, I'll give it another shot.
 

Paperdoc

Polypheme
Ambassador
If you use a third-party fan controller, you do NOT get automatic control of that fan in any way. YOU will have total control of what the fan does, so you'll have to turn it on or off.

It is not clear whether you want that fan to go on at full speed whenever you want it running, or whether you want it to vary its speed according to temperatures, but just not run when your system is cool. So I'll give you two options. Now, because your mobo will send the fan a power supply of varying voltage, it would be hard to get it to run at full speed all the time, but I'll give you a suggestion at the end.

First, the hardware limits and capabilities. The fan you specified is a 4-pin PWM type fan. Look at its cable closely. I expect it has 4 wires, and ends in a female connector with 4 holes. That fan type CAN be controlled by EITHER method of fan control - PWM or Voltage Control Mode. your mobo has two SYS_FAN headers, and each of them uses only Voltage Control Mode. So those headers CAN control the speed of your fan.

Now, how to do ...

1. You can try to do this with a custom "fan curve" you can create in BIOS SETUP and let the mobo header control the fan for you completely. See your manual, p. 13. There is a box with eight entries in it to define four points on the fan curve shown to the right, and it will have some default values in there. Change them to suit your needs. I suggest you start with setting the first two temperatures at 40 and 60, then set the first two speeds to 0 each. IF it lets you do that, this will keep the fan from coming on until after the temperature exceeds 60. Then set the third and fourth temps to, say, 70 and 90, and set the last two fan speeds to 70 and 100. This will cause your fans to stay off until about 60 degrees, then rapidly speed up at higher temperatures.

2. IF you only want your fan to turn on only when you flip a switch, and then run varying speeds under motherboard automatic control until you turn it off, you can do this with a relatively simple mod of the fan wiring and by installing a small switch somewhere easy to access. First, identifying fan leads. Look at the female header on the end of the fan leads. Along one side are two ridges that align with a plastic tongue on the mobo header. The ridges are just outside Pin #1 and Pin #3. Pin #4 is at one end beyond the nearby ridge. You need to work on the wire coming from Pin #2 to the fan. This is the DC voltage supply to the fan. Cut that wire at one spot, and solder a new 2-conductor wire to the two ends you just created. Insulate the joints with tape. Run your new wire to wherever your new switch it located and solder its ends to the two terminals of the switch. Now you can turn the fan off or on with that switch. When it is on, the fan speed will be controlled by the automatic settings in that fan curve from p. 13. You can adjust that if you wish. IF you find that trying my first suggestion of a custom fan curve can not actually shut the fan off at low temperature, adding this switch mod can allow you to shut it off manually, or choose automatic control when you want it at higher temperatures.

If you want your fan to run at full speed almost all the time when you have it switched on, try setting the fan curve on p.13 to go to 100 speed for all the upper temperatures.

Two additional notes.

(a) when you turn off your fan, you MAY get a fan failure warning because the fan has no speed. Or, your mobo may not do that.
(b) When you make any custom settings in BIOS Setup (e.g., on p. 13 fan curve), remember to SAVE and EXIT from Setup so your new settings are saved.
 
Solution
Jun 3, 2017
6
0
510
Thanks Paperdoc. You truly are the grand master of fan configuration. I decided to go with the PCI fan controller I mentioned above. A PCI controller was always my preferred solution. I just couldn't find one that turned fans off until now. I'm picking you as the best solution because you dropped a nuclear knowledge bomb on this thread.
 
Jun 3, 2017
6
0
510
Update: The fan controller works great. I plan on incorporating it into builds in the future. There are a lot of cases that have mountings for fans on the top. This is great for cooling but usually creates negative air pressure that attracts dust. Now I can have a positive pressure build that I can convert to negative pressure by turning on top mounted fans when I want an extra boost of cooling.