Question Setting fan curve to 0 rpm

[WalterMelon]

TLDR: I want to keep fans off until the temps start to rise. My old DC fans couldn't be set to <60% in the bios fan curve. Can PWM fans be kept off till temps hit 50° or so do they also have to also be above a minimum?

 

[zinkles]

Can PWM fans be kept off till temps hit 50° or so do they also have to also be above a minimum?

If the BIOS supports it (or through software), you can set it to be OFF till temps start rising.

 

[Paperdoc]

Older 3-pin versus newer 4-pin PWM has almost NO influence on this question. Voltage Control Mode and PWM Mode are only signal METHODS for setting a fan speed. Deciding what speed is required is a separate question - that is the fan Profile option.

Your mobo's fan header Profile options MAY include an ability to allow the fan to shut off, OR it may actually refuse to let you do that. When you go to set up your own custom "fan curve" it may impose no restrictions so that you need to get it right. Or it may prevent you from letting it stall. It all depends on how your mobo is designed.

My "almost" adjective is because there is a small effect that still is important, with two aspects. Every fan has a Stall Speed - if you try to get it slower than this it will stall and NOT re-start until the control signal (of whichever form) is raised sufficiently. Then the related Start-up signal (again of whichever type) is the minimum required to get a stalled fan to re-start. For an older 3-pin fan system this may be 5 VDC minimum Voltage to avoid stalling, and min 7 VDC to start up a stalled fan. For a 4-pin style of fan fed by PWM Mode signals, same principle but I can't suggest the exact numbers. The ONLY difference here is that it appears the PWM-style fan motor can avoid stalling at a slightly lower minimum speed, and can be re-started at a slightly lower speed.

Be aware of this factor also. Most mobo fan headers have a stall-prevention feature by default. One important function it has always is to monitor the fan speed for NO fan speed signal, indicating fan FAILURE. If that happens, the normal corrective action is to increase the fan speed signal significantly (a higher speed, or even full speed) and watch the speed signal. IF the fan re-starts then the header automatic control system re-sends out the speed control signal it was sending before the failure and the fan resumes the earlier performance. If that setting was so low that it caused the stall, the whole process will repeat over and over. IF the fan does NOT re-start, you get a prominent warning on your screen so you know there is a problem. For the CPU_FAN header (and some associated headers) in particular, the corrective action will be more intense. If the attempt to re-start fails too, it may shut you down completely to protect the CPU from rapid overheating when there is NO cooling. The actions for SYS_FAN or CHA_FAN, though, are the simpler screen warning. Many headers have an option to IGNORE the speed monitoring for failure process so you can choose to get NO warning or corrective actions if that fan stalls. If your header has an option to allow the fan to stop below a certain temperature, this no-alarm option is included for that specified low temperature range.

 

[WalterMelon]

If the BIOS supports it (or through software), you can set it to be OFF till temps start rising.

I might just be missing it but my new MSI b650 doesn't seem to have this ability. I can set a custom curve, constant speed, or disable it (nothing else). I'm 100% sure that my older (Ivy Bridge and Kabby Lake)Asus boards don't have the option. Asus went let me set ia curve bellow the fans minimum rpm. MSI lets me set it to zero but will still spin at the minimum.

Older 3-pin versus newer 4-pin PWM has almost NO influence on this question. Voltage Control Mode and PWM Mode are only signal METHODS for setting a fan speed. Deciding what speed is required is a separate question - that is the fan Profile option.

Your mobo's fan header Profile options MAY include an ability to allow the fan to shut off, OR it may actually refuse to let you do that. When you go to set up your own custom "fan curve" it may impose no restrictions so that you need to get it right. Or it may prevent you from letting it stall. It all depends on how your mobo is designed.

My "almost" adjective is because there is a small effect that still is important, with two aspects. Every fan has a Stall Speed - if you try to get it slower than this it will stall and NOT re-start until the control signal (of whichever form) is raised sufficiently. Then the related Start-up signal (again of whichever type) is the minimum required to get a stalled fan to re-start. For an older 3-pin fan system this may be 5 VDC minimum Voltage to avoid stalling, and min 7 VDC to start up a stalled fan. For a 4-pin style of fan fed by PWM Mode signals, same principle but I can't suggest the exact numbers. The ONLY difference here is that it appears the PWM-style fan motor can avoid stalling at a slightly lower minimum speed, and can be re-started at a slightly lower speed.

Be aware of this factor also. Most mobo fan headers have a stall-prevention feature by default. One important function it has always is to monitor the fan speed for NO fan speed signal, indicating fan FAILURE. If that happens, the normal corrective action is to increase the fan speed signal significantly (a higher speed, or even full speed) and watch the speed signal. IF the fan re-starts then the header automatic control system re-sends out the speed control signal it was sending before the failure and the fan resumes the earlier performance. If that setting was so low that it caused the stall, the whole process will repeat over and over. IF the fan does NOT re-start, you get a prominent warning on your screen so you know there is a problem. For the CPU_FAN header (and some associated headers) in particular, the corrective action will be more intense. If the attempt to re-start fails too, it may shut you down completely to protect the CPU from rapid overheating when there is NO cooling. The actions for SYS_FAN or CHA_FAN, though, are the simpler screen warning. Many headers have an option to IGNORE the speed monitoring for failure process so you can choose to get NO warning or corrective actions if that fan stalls. If your header has an option to allow the fan to stop below a certain temperature, this no-alarm option is included for that specified low temperature range.

I mentioned pwm because DC fans won't spin up at a low voltage so the minimum is much higher AND it's potential fire issue. Since PWM is applying the full voltage in short bursts instant on,off,on,off cycles are perfectly safe.

I'm familiar with the warning screens your talking about. I had to adjust the 400rpm warning to 200rpm with ever time I got a new Mobo or reset bios because CM 230mm fans idle just under 300rpm.

But none of that is an issue here. I want 2 of sys fans just off completely til the system gets hot. Like PSU fans and laptop fans. I don't think there's a way to do it.

 

[zinkles]

Since there isn't a way in the BIOS, the best yo can do is to set the fan speed in the fan curve to the lowest it supports and then at the temp you want it to spin up, set it to a higher fan speed.

 

[Paperdoc]

The only other place to look I can suggest is in the MSI Centre app that came with the mobo. It has some tools for fan adjustment, but I don't know if ability to stop is included.

By the way, I think you understand the impact of speed settings too low. My way of looking a that is this. For older Voltage Control Mode (3-pin) fans, if you feed one a Voltage too low it will stall. Once it is stalled and NOT re-started, there still is a Voltage supplied to the motor coils and a current DOES flow through the coils, BUT not sufficient to create movement. So the only thing limiting that current is the static resistance of the coils, and they will generate heat from current flow. However, there is NO air flow generated over the fan chassis, so there is NO normal cooling of the motor. Thus is will heat up to some unpredictable temperature as long as this low Voltage is still applied. So the only safe way to make the fan stop is to shut off the Voltage supplied, NOT simply to reduce to a "low" voltage. Now, for PWM fans the same sort of reasoning applies, except that what has to be set down to zero is the PWM signal, not the fixed +12 VDC supply on Pin #2. (However, setting the supply Voltage to zero also would work very well.) I do see your point: a PWM signal for ZERO Time On would prevent any flow of current through the windings and hence prevent heating of the stationary coils.

 

[WalterMelon]

Ironically I figured it out yesterday by trial and error. Just switch to DC instead not PWM.
Setting a PWM point anywhere between to 0-16% spins at just over 40% (600rpm).
Setting PWM to 17% does spin at 300-350rpm (over 17% but still much lower).

Using an adjustable DC PSU I figured out all my fans will spin at 4.5-5v. So,
I set 4 of the 6 intake fans to 0.0v til 50°, 6.0v at 51°. At 6.0v they spin at about 50% max rpm.