pwm fans slower in game then when not

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sid3ffect

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Jan 31, 2015
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my pwm fans will slow down about 200 rpm while in game or while the pc is under a load (i.e., stress tests)... they will still spin faster as the pc heats up but then once i exit the game or stop the stress test they will spin up about 200 rpm or so and slowly go down as the pc cools.

asus maximus vii formula z97 mobo
fans are powered via a molex splitter with a pwm header to the mobo for pwm control and rpm feedback
noctua ippc 2000 pwm fans... mixed 120mm and 140mm... 5 120's that are on the radiators are on one header... 3 140's and 1 120 are on a different header as "breathing" fans
 
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ihog
Eh, that sounds pretty much normal. They have a set RPM when nothing's running, then they drop down when the game isn't taxing the system too much, then they ramp up when heat ramps up to keep steady temps, ramps up even more get rid of heat once the game stops to more quickly bring the temps down, and then slows down again as temps go down.

That's what PWM fans do: they adjust RPM relative to temps/activity.
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ihog

ihog

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You say the PWM fans are slower in game than out, but what you're describing is the opposite.

Could you please try explaining more thoroughly? What the PWM fan speeds at the desktop? What are they in game/stress test? What are they after closing the game/stress test?
 
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sid3ffect

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Jan 31, 2015
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so, at desktop, let's say the fans are going at 500 rpm... I fire up a game and they will drop down to like 300... as the pc gets warmer they will steadily rise to compensate for the added heat to say 800rpm... I quit the game and they will shoot up to 1000rpm and steadily go back down to 500 as the pic cools.

I see it like this, it's sort of like there is too much power draw on the system and the loss of available power causes them to not be able to spin as fast... ever turn on your clothes dryer and notice the lights dim briefly? kinda like that.

but I'm pretty sure it's not a power draw issue because I tried turning the pwm functionality off altogether and just set the fans to 100%, fired up a game and the fans didn't even flinch... they stayed at full rpm the whole time.

thanks!
 
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ihog

ihog

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Eh, that sounds pretty much normal. They have a set RPM when nothing's running, then they drop down when the game isn't taxing the system too much, then they ramp up when heat ramps up to keep steady temps, ramps up even more get rid of heat once the game stops to more quickly bring the temps down, and then slows down again as temps go down.

That's what PWM fans do: they adjust RPM relative to temps/activity.
 
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sid3ffect

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Jan 31, 2015
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I have little experience with pwm fans, I would think with activity and temps being high that they would work harder... not wait till activity is low to bring temps down.

but anyone would know better than me at this point so I appreciate your input...

is there any one point of thermal monitoring that is more preferred for pwm fans to react off of? I had them originally set on the cpu but the on board cpu temp sensor fluctuates so frequently and drastically that the fans would do the same. So, I installed a temp probe into my cooling loop and currently have the fans react to that.

thanks again!
 
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ihog

ihog

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Well, if it happens the way you described, the fan doesn't ramp up ALL the way while gaming because it is keeping temps in line while not making too much noise. Then it ramps up quickly to lower temps, because it won't be running that fast for long. This behavior is even more likely since they aren't aligned to the CPU or GPU temps.

Where in your loop is the temp probe?
 
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ihog

ihog

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That's kinda not the best idea, since the temp of your CPU cores/GPU can vary from ~30C to ~90C, while your water temps aren't going to be more than 10-20C higher than your room temperature. The PWM won't really ramp up that much or accurately.
 
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sid3ffect

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Jan 31, 2015
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all due respect...

if I was air cooling the pc, I would agree with that but I just don't see how the fans spinning up to 80-100% when the core temps go up is going to effect the overall efficiency of the cooling loop... the core temps on my setup will hit 80-90c on a stress test (maximum heat output) no matter how cool the water is in the loop. so this is why I have the fans react to the temp of the coolant instead.

the temp of the cpu at the on board sensor fluctuates very drastically based on its current clock speed, voltage and load and linking my fans to this sensor causes the fans to overreact

getting back to the topic however, I can agree with this just being the natural behavior of pwm and I'll just consider it normal... I am thinking that I would maybe like to move the temp probe to the cpu water block right next to the die though. I think temps here are naturally going to be warmer than that of the coolant and this with a less aggressive fan curve would probably be just fine.

thanks again for your input!

cheers
 
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