Author Topic: Tone sound on fan  (Read 2990 times)

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Offline DavidDLC

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Tone sound on fan
« on: April 06, 2011, 09:30:58 pm »
I recently added a PWM controller to my desk fan in order to be able to modify the speed and therefore the amount of breeze.

I can notice a squeak sound about 1 KHz I will say coming from the motor, and I want to get rid of it, what kind I do ?

Regards.

 

Offline dimlow

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Re: Tone sound on fan
« Reply #1 on: April 06, 2011, 09:32:59 pm »
Up your PWM frequency, I did that same once, the tone gets real annoying after a time
 

Offline Simon

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Re: Tone sound on fan
« Reply #2 on: April 06, 2011, 09:38:35 pm »
When you power a motor the rotor will push forward as well as go round. if your using PWM to control it the shaft will oscilate making the buzing sound. I once knocked up a quike PWM controller for an 84W can blower to use at work, I soon installed an optional capacitor to increase the frequency. Lower frequencies got me more power less heating in the control transistor and a sqeek. The high frequency was silent but needed more power for the same speed but was more controllable at low speeds
 

Offline Trigger

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Re: Tone sound on fan
« Reply #3 on: April 09, 2011, 05:57:50 pm »
Somewhat related.  I remember a talk at Blackhat that used that effect with some modulation to send the users password to a listener with a directional microphone and some signal processing.

http://www.blackhat.com/presentations/bh-usa-08/Filiol/BH_USA_08_Filiol.zip
Here, took me a bit to find it in the archives but it's interesting.
 

Offline scrat

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Re: Tone sound on fan
« Reply #4 on: April 11, 2011, 02:44:21 pm »
Of course the increasing the PWM frequency will work.
Why not trying with a little L-C filter, to smooth out the PWM carrier?
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Offline Simon

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Re: Tone sound on fan
« Reply #5 on: April 11, 2011, 04:08:33 pm »
well thought that PWM gave more torque to the fan at lower speeds than controlling the speed with lower DC voltages which is what an LC filter would do
 

Online Zero999

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Re: Tone sound on fan
« Reply #6 on: April 11, 2011, 04:43:31 pm »
Try increasing the frequency.
 

Online NiHaoMike

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Re: Tone sound on fan
« Reply #7 on: April 11, 2011, 07:14:31 pm »
Another trick is to try a spread spectrum clock.
Cryptocurrency has taught me to love math and at the same time be baffled by it.

Cryptocurrency lesson 0: Altcoins and Bitcoin are not the same thing.
 


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