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 Post subject: Where does the fan clicking sound come from ?
PostPosted: Tue Mar 09, 2004 3:27 am 
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Joined: Tue Mar 09, 2004 3:15 am
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Anybody got any idea where does the clicking sound of most undervolted fans come from ? A dissasembled a few of them and can't see nothing that would cause the clicking ? Are the sleeve bearing ones without these problems ?


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PostPosted: Tue Mar 09, 2004 4:02 am 
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Joined: Tue Jan 20, 2004 8:24 pm
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No, sleeve bearing fans have the problem too--just look at Papst and Panaflo!!!!

In fact, the clicking noise has nothing to do whatsoever with the bearing--it comes from the MOTOR. Basically, as I understand it, the clicking noise happens because most DC brushless motors use a square-wave type stator motion, and as a result, each time one of the coils is energized, it causes a sudden burst of torque at that brief moment, which causes a minute contracting of the entire fan structure. I expect the intensity of the clicks probably has something to do with the tolerances inside the motor housing--is anyone out there more expert than me on this willing to come forward and say for sure?!? :?:


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PostPosted: Tue Mar 09, 2004 5:54 pm 
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Joined: Fri Aug 01, 2003 10:45 pm
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Location: North Billerica, MA, USA
Not an expert, but my understanding is the same as yours about the square wave stator pulses causing acceleration and deceleration. Per the physics laws about conservation of angular momentum, if the blades are accelerating in one direction, the frame must be accelerating in the opposite direction. If there is any slop in the housing or in the fan mounting I would expect it to get 'worked' back and forth which might give the click...

Gooserider

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PostPosted: Tue Mar 09, 2004 7:06 pm 
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Joined: Tue Jan 20, 2004 8:24 pm
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Gooserider wrote:
Per the physics laws about conservation of angular momentum, if the blades are accelerating in one direction, the frame must be accelerating in the opposite direction. If there is any slop in the housing or in the fan mounting I would expect it to get 'worked' back and forth which might give the click...

Makes sense to me. In other words, if it does NOT click, it is probably a sign that motor housing was built to finer tolerances than one that does click.


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PostPosted: Sat Mar 13, 2004 5:39 pm 
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Joined: Fri Aug 01, 2003 10:45 pm
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Location: North Billerica, MA, USA
Right, and I also suspect that mounting has something to do with it as well - IIRC, I've seen reports of fans that don't click when held in the hand, but did when bolted to a case. That would indicate to me that there is a problem with the damping of the fan mounts - either there is slop in the mounting hardware, or the panel has slop where it's connected to the rest of the PC. Also note the many reports that decoupling reduces or eliminates the click.

Gooserider

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Building Dual Athlon MP system, Tyan mobo, U160 drives, Server Cube case, Linux ONLY, lots of other goodies. Will water cool, attempting to make as silent as possible.


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