Fan speed drops 47% randomly

[Jahngoh]

My fan speed is randomly dropping to 600rpm. I always have to open up speed fan and change it back to 100%. Any idea what might be causing this?

Cool n' Quiet is disabled btw.

 

[Zepper]

. First, which fan is it: system, CPU? What brand and model fan is it? Please be specific and detailed in your questions - most of us are not clairvoyant.
. Most current mobos have fan speed control built into the BIOS (mine gives a little beep thru the system speaker when it changes speeds). It can change the speed of the fan based on the temperature. This feature can usually be disabled in the BIOS and/or in the hardware monitor software that came with the mobo. I always recommend to use the hardware monitor software that comes with your mobo as it should support any special features like that better than the generic software like SF.
. And then your fan may have a built in temperature sensor which should be disabled if you are using some other form of speed control.

.bh.

 

[BonzaiDuck]

I don't know the technical specifics as to why this happens, but it can be related to the "start" voltage of the fan.

Tell us what fan you're using.

Some mobo software "might" enable a fan-control function, but the ASUS software for my boards isn't that sophisticated. I've had very good and reliable results with SpeedFan. There are some advanced settings which may change the way SF controls the fan.

There is a threshold below which SF is unable to keep the fan speed where you want it, and I think this has to do with the fan specs.

I have a Delta Tri-Blade 120x38mm on my CPU cooler. I've been trying to reduce noise even further (it's already a whisper) -- and I was experimenting with the settings. When I drop the minimum speed setting down below some 46% of "full" -- the same thing happens with mine which happens with yours. I'm sure it has to do with "start" voltage, or the fan-motor's capabilities.

You'd have to look into it more -- I'd appreciate being "corrected" here in this thread, also -- but SF uses "PWM" or "pulse-width-modulation" for fan-speed control. I do not think it changes the voltage going to the fan, but varies the continuity of the power.

It seems I might be contradicting myself in this post, so I hope my remarks are helpful, anyway.