Fan percentage and rpm

[Robinskix]

Quick question about fan rpm vs percentage.

I have allways wondered about the corrolation between the fan percentage and the actual rpm. For example hwmonitor shows 35 % on a fan. and that fan fluctuates between 800 and 810 rpm. Does that mean that it is not actually steady at 35 % or is there something else that causes that fluctuation like voltage fluctuations. In this case its a gpu fan.

Just wondering what actually causes that minute rpm fluctuation

 

[weberdarren97]

Simply put, the tachometers on many fans (the part that measures RPM) are not entirely accurate. They may show fluctuations of less than 50 RPM when in fact the fan is spinning at a steady RPM. However this is not always the case.

Since it's on a graphics card, it's likely that it's just getting the leftover power after the GPU itself does the instructed work (like rendering a display). If this is the case, voltage may fluctuate slightly and there's nothing you can do about this that wouldn't void your warranty on the card.

Either way, it's nothing to worry about.

 

[ss202sl]

Can something in the air(dust particle) hit the fan and cause it to slow from 810 to 800RPM? You're only talking about a 1% fluctuation, so it's not a lot, and voltages can certainly fluctuate that much.
https://www.lifewire.com/power-supply-voltage-tolerances-2624583

 

[weberdarren97]

Can something in the air(dust particle) hit the fan and cause it to slow from 810 to 800RPM? You're only talking about a 1% fluctuation, so it's not a lot, and voltages can certainly fluctuate that much.
https://www.lifewire.com/power-supply-voltage-tolerances-2624583

A dust particle hitting the fan wouldn't slow it down. A dust particle caught up in the bearings might cause a slight change in speed, but this is usually accompanied by the fan making unhealthy sounds.

As for the voltage fluctuations, up to 10% is allowed on the 12V rail so 12V could be anywhere from 10.8V to 13.2V. I usually don't use power supplies that show more than a 5% fluctuation on the 12V rail unless I'm putting it in an experimental system that I really don't care about that much.

If when load changed, 12V went from say 12.4V to 11.9V, this would be acceptable but would cause a change in the behavior of the VRMs on the card, possibly causing the amount of leftover power to change which could slightly change the speed of the fans until the card corrects for the change in voltage which tends to take about .003 seconds on newer cards.

Bottom line, this behavior is normal and there's nothing to worry about here.