Author: parsec
Subject: How to turn pwm fans off at idle - h170
Posted: 23 Nov 2016 at 9:27am
After testing the various fans on my ASRock Z170 board, both PWM and three pin voltage controlled, using my board's A-Tuning utility, the minimum speed I could set the fans at was their 10% speed, as shown after running the FAN Test function that is available for each fan.
That is, after setting the fan speed % to zero. I set the temperature (vs fan speed) high enough so the CPU temperature would not influence the fan speed.
So the reality of the fan speed control, as far as I can see, is while there is a zero fan speed setting, the actual minimum fan speed possible is 10%. The minimum fan speeds you posted seem to be the same, a bit lower than the fan speed specifications, but certainly about as low a PC fan can operate.
Franky, the ability to completely turn off a PC fan with a board's fan speed control is virtually non-existent. I've never owned a mother board whose fan speed control allowed turning off a fan completely. Actually, some older boards I've owned would issue a fan speed warning when the PC started, if the fan on the CPU Fan header was less than ~500 RPM. There are multiple reasons why the fan speed control on mother boards does not allow a fan speed of zero.
There are no standards for the minimum speed of a fan, their starting voltage, or speed (RPM) vs voltage or applied PWM signal level. All fans have different minimum speeds, but more significantly, have different minimum starting voltages. Dealing with the range of minimum and maximum fan speeds, and different starting voltages with all the fans that could be used is difficult.
But the biggest problem with low or zero fan speed settings, is the starting voltage of a fan (the minimum voltage applied to a fan that will cause it to spin) is greater than the voltage needed to maintain the minimum fan speed possible.
It takes more voltage sent to a fan's motor to initiate spinning, than it does to maintain the minimum speed of a fan that is already spinning. So we would think, simply apply more voltage to a non-spinning fan, to get it started. Doing that is not as easy as it sounds. Since the starting voltage of fans are not the same, the difference between the minimum spinning voltage and starting voltage of a fan may be as much as three to five volts, but as low as one or two volts.
If the minimum fan speed voltage is much lower than the starting voltage, then the fan will suddenly begin spinning at a rate that will be higher than the minimum fan speed expected. Then the fan voltage should be reduced, to match the minimum fan speed possible. But how much do we reduce the voltage, without going below the minimum fan speed voltage? This situation leads to fan speed "pumping", where the fan becomes audible when it is forced to start, but then reduced again to a lower speed.
That is a simplification of only two factors related to the difficulty of providing zero fan speed control.
Finally, mother board manufactures are reluctant to provide zero fan speed control, assuming it is even possible. If a CPU or other components over heat due to the user using zero fan speeds, guess who gets the blame? It's not the user.
So sorry, we simply cannot turn off the fans completely with automatic fan speed control. If you want to do that, you'll need a manual fan speed controller.
Also, if your fans are audible at their 10% speed level, then they have a very high minimum speed. The minimum fan speeds you listed in your post should be inaudible, or so close to it that the difference between 10% speed and zero, should be inaudible.
Subject: How to turn pwm fans off at idle - h170
Posted: 23 Nov 2016 at 9:27am
After testing the various fans on my ASRock Z170 board, both PWM and three pin voltage controlled, using my board's A-Tuning utility, the minimum speed I could set the fans at was their 10% speed, as shown after running the FAN Test function that is available for each fan.
That is, after setting the fan speed % to zero. I set the temperature (vs fan speed) high enough so the CPU temperature would not influence the fan speed.
So the reality of the fan speed control, as far as I can see, is while there is a zero fan speed setting, the actual minimum fan speed possible is 10%. The minimum fan speeds you posted seem to be the same, a bit lower than the fan speed specifications, but certainly about as low a PC fan can operate.
Franky, the ability to completely turn off a PC fan with a board's fan speed control is virtually non-existent. I've never owned a mother board whose fan speed control allowed turning off a fan completely. Actually, some older boards I've owned would issue a fan speed warning when the PC started, if the fan on the CPU Fan header was less than ~500 RPM. There are multiple reasons why the fan speed control on mother boards does not allow a fan speed of zero.
There are no standards for the minimum speed of a fan, their starting voltage, or speed (RPM) vs voltage or applied PWM signal level. All fans have different minimum speeds, but more significantly, have different minimum starting voltages. Dealing with the range of minimum and maximum fan speeds, and different starting voltages with all the fans that could be used is difficult.
But the biggest problem with low or zero fan speed settings, is the starting voltage of a fan (the minimum voltage applied to a fan that will cause it to spin) is greater than the voltage needed to maintain the minimum fan speed possible.
It takes more voltage sent to a fan's motor to initiate spinning, than it does to maintain the minimum speed of a fan that is already spinning. So we would think, simply apply more voltage to a non-spinning fan, to get it started. Doing that is not as easy as it sounds. Since the starting voltage of fans are not the same, the difference between the minimum spinning voltage and starting voltage of a fan may be as much as three to five volts, but as low as one or two volts.
If the minimum fan speed voltage is much lower than the starting voltage, then the fan will suddenly begin spinning at a rate that will be higher than the minimum fan speed expected. Then the fan voltage should be reduced, to match the minimum fan speed possible. But how much do we reduce the voltage, without going below the minimum fan speed voltage? This situation leads to fan speed "pumping", where the fan becomes audible when it is forced to start, but then reduced again to a lower speed.
That is a simplification of only two factors related to the difficulty of providing zero fan speed control.
Finally, mother board manufactures are reluctant to provide zero fan speed control, assuming it is even possible. If a CPU or other components over heat due to the user using zero fan speeds, guess who gets the blame? It's not the user.
So sorry, we simply cannot turn off the fans completely with automatic fan speed control. If you want to do that, you'll need a manual fan speed controller.
Also, if your fans are audible at their 10% speed level, then they have a very high minimum speed. The minimum fan speeds you listed in your post should be inaudible, or so close to it that the difference between 10% speed and zero, should be inaudible.