Question Weird case fan behaviour

Jul 17, 2013
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My god it kills me....dont know what to think anymore.........so i need your help guys because i can't take it anymore.
So i have just installed some new run of the mill fans(Arctic f12 120mm) for my case/Segotep lux black.I replaced the 2 ones on top. the one in the front is giving me headaches.
So i have a 120mm magnetic dust filter on it for intake(yeah i know its not ok but it works nice,the one on the top back is for exaust without dust filter and also one on the rear near i/o for exaust still without filter.
Problem is the top front one without dust filter works ok,the airflow is massive,but with dust filter turns into a airplane turbine (obviously with less air into the case but also its like going into reverse with a lot of air coming out through the dust filter towards outside.
Yes i know the correct airflow direction.If i hover my hand over it like 5 cm its normal but if i close in like 2-3 cm(not covering it completely) it starts the plane.Wtf ?
Does it have a sensor on it or something to let it know to ramp up if something is in the way?
I connected it to power supply directly not through motherboard headder.My temps are also very good with 19-20c average room temp the motherboard sits at 24-25 and cpu at 26 idle so its very cool.
What gives ?
Also with my hand just hovering over it like 3-4 cm when it starts plane mode, the output inside the case is very diminished.
I have also tested the fan outside of the case,plugging the intake with just the dust filter.Its normal sound.
The only thing different between outside testing and inside case testing is that the case has grating with .5 or so cm holes on it.
I can't really explain properly whats happening so if you ask i give any info necessary.
With the old fan nothing like this happened.
 

Eximo

Titan
Herald
Weirdly this is an effect of restricted airflow. With less air traveling through the fan, less work for it to do, so it speeds up. Only way to counteract that would be to reduce the fan speed itself, which in reality you are controlling power not speed.

Having two types of mesh on top of each other can create some serious flow restrictions. If there is a way to keep the filter from directly touching the case's metal, that should help as well.
 
Jul 17, 2013
17
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10,515
0
Yes that was it i put the connector into motherboard header and started up at normal speed 650 rpm..max is 1350 so yeah it was running at full speed,made a speed curve for them and now i barely hear them at 970-1000 rpm thank you very much for the solution !
 

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