Fast, Slow, Barely Moving, Jet Take-Off, Slow...

The VCR King

The VCR King

Well-Known Member
I have noticed that the 140mm fan in my computer case has been behaving quite erratically lately. One minute it's barely spinning, the next, its spinning like it about to prepare for take-off, then the next minute it's back to normal. This fan is plugged directly into a 3-pin port on my motherboard. Is the motherboard controlling the fan speed/voltage or is yet another part of my computer about to take a crap? :confused:
 
If it's plugged into a fan header then yes the motherboard is controlling the speed.
 
Why would it auto control the fan--is it like:
"Gees, this room is hot. Better turn this thing up and get a breeze goin'!"
"Gees, this room is cold. I don't really need this fan. I'll turn it down."
 
Correct. It all depends on what temperatures the sensor is detecting. If you want to modify the settings, poke around in your BIOS for fan control settings.
 
Alright, because all of my case fans are running insanely slow now that it is getting colder here in Ohio. Besides, our furnace just failed a few days ago so our house stays at about 59 degrees upstairs. :(
 
The Blue Beast said:
Alright, because all of my case fans are running insanely slow now that it is getting colder here in Ohio. Besides, our furnace just failed a few days ago so our house stays at about 59 degrees upstairs. :(
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If there's not much excess heat then why would you want jet engine fans anyway? It's fine that they spin slowly.
 
You could try changing the fan profile in BIOS. If it's erratically changing in speed pretty rapidly then try disconnecting it and spinning it by hand. If it doesn't spin easily like the others then you may have a bearing type of issue. Sometimes the system tries to compensate by adding additional voltage to the fan if the bearing is seizing/dragging the RPM down, which ends up throwing it past the defined goal RPM. Then you have a situation of fast/slow as it tries to achieve the goal RPM instead of just a consistent speed.
 
I've been monitoring the fan voltages in SpeedFan (it's a 12-v fan BTW) and I've noticed the fan trying to be ran at 15 volts and I've seen it drop down to 7v. I took out the fan and spun up it by hand and it was smooth. The dust filter is clean and the bearings are good.
 
It decreases and increases voltage to change the speed of the fan. That's why you see the voltages drop and rise.

Like both Beers and myself said, it's controlled in the BIOS and you should change it in there if you want it to stop revving high and low.
 
Well obviously the computer is slowing down the fans because the room is colder and they aren't needed as much or they are sped up because the room is hot and the PC requires a breeze. I'm okay with this because at least slowing them down saves a bit of energy.

I do think that the MOBO is controlling all fan power, and not just the motor, because when the fans slow down the LEDs dim slightly as well.
 
The Blue Beast said:
Well obviously the computer is slowing down the fans because the room is colder and they aren't needed as much or they are sped up because the room is hot and the PC requires a breeze. I'm okay with this because at least slowing them down saves a bit of energy.

I do think that the MOBO is controlling all fan power, and not just the motor, because when the fans slow down the LEDs dim slightly as well.
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I wouldn't take it as that obvious if you had to make a thread about it ;). Also, the energy saved is extremely negligible.

The LEDs dim because the voltage to the fan dropped and they're tied to the same circuit. All a fan controller does is adjust voltage.
 
Its gotten so cold in here that the motherboard is running all of my (12V) fans at 5 volts... this thing is practically silent... :rolleyes:
 
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