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'[EE] Fan noise with PWM power'
2007\01\13@041450 by Rob Hamerling

face picon face
I wanted to smooth noise of the airflow produced by the case-fan of my PC.
I made a simple circuit with a PIC12F683, a temperature sensor as
inpout and a PWM signal as output to control the speed of the fan.
That works, but now the fan produces a mechanical noise, apparently
with the PWM frequency. I have tried PWM frequencies between 60 and
500 to see if I just hit a resonance frequency of the fan, but the
noise remains.
Any suggestion (where to find info) on how to smooth this noise?

Regards, Rob.

--
Rob Hamerling, Vianen NL (http://www.robh.nl/)

2007\01\13@050208 by Wouter van Ooijen

face picon face
> Any suggestion (where to find info) on how to smooth this noise?

Is it a fan with electronics?

maybe you can use >20 kHz PWM?

Or: why PWM at all? Smooth the PWM output with an RC and feed a current
source (BD139 or similar with R in emitter-to-groun).

Wouter van Ooijen

-- -------------------------------------------
Van Ooijen Technische Informatica: http://www.voti.nl
consultancy, development, PICmicro products
docent Hogeschool van Utrecht: http://www.voti.nl/hvu


2007\01\13@054107 by Marcel Buijs

flavicon
face

Rob,

Perhaps it's better to controll the DC current throug the motor by the PIC,
instead of using PWM.

pic controlling DAC with (DC current) powerdriver.

Best regards,
marcel.
(haven`t starting programming pic's yet.)

-----Oorspronkelijk bericht-----
Van: spam_OUTpiclist-bouncesTakeThisOuTspammit.edu [.....piclist-bouncesKILLspamspam@spam@mit.edu]Namens Rob
Hamerling
Verzonden: zaterdag 13 januari 2007 10:15
Aan: PIClist
Onderwerp: [EE] Fan noise with PWM power


I wanted to smooth noise of the airflow produced by the case-fan of my PC.
I made a simple circuit with a PIC12F683, a temperature sensor as
inpout and a PWM signal as output to control the speed of the fan.
That works, but now the fan produces a mechanical noise, apparently
with the PWM frequency. I have tried PWM frequencies between 60 and
500 to see if I just hit a resonance frequency of the fan, but the
noise remains.
Any suggestion (where to find info) on how to smooth this noise?

Regards, Rob.

--
Rob Hamerling, Vianen NL (http://www.robh.nl/)

2007\01\13@071052 by Anand Dhuru

flavicon
face

>
> Rob,
>
> Perhaps it's better to controll the DC current throug the motor by the
> PIC,
> instead of using PWM.
>
Absolutely. These fans are brushless motors with a hall effect sensor;
feeding PWM to the DC input lines would do crazy things to the drive
circuit. Lowering the voltage seen by the fan's DC input reduces the RPM
quite reliably.

Regards,

Anand

2007\01\13@071329 by Richard Prosser

picon face
Try adding a LC filter so the fan  only gets fet the DC component -
not the raw PWM.  With raw PWM the fan is still seeing the same peak
voltage which may (or may not) correspond to the switching point of
thefan driver.

RP

On 13/01/07, Marcel Buijs <Marcel.BuijsspamKILLspamwxs.nl> wrote:
{Quote hidden}

> -

2007\01\13@074131 by Rob Hamerling

face picon face

Hi Wouter,

[RobH]
> I made a simple circuit with a PIC12F683, a temperature sensor as
> input and a PWM signal as output to control the speed of the fan.
> That works, but now the fan produces a mechanical noise, apparently
> with the PWM frequency. I have tried PWM frequencies between 60 and
> 500 to see if I just hit a resonance frequency of the fan, but the
> noise remains.

Wouter van Ooijen wrote:
>> Any suggestion (where to find info) on how to smooth this noise?
>
> Is it a fan with electronics?

Don't know. I tried different (pretty old) fans, all behave similarly.

> maybe you can use >20 kHz PWM?

Must be possible. In the meantime I found an example in a Predko book
which uses a 10 KHz PWM.

> Or: why PWM at all?

Well, I used as example the circuit of Jos van Eijndhoven
(http://jos.vaneijndhoven.net/fancntl/index.html).
I liked its simplicity.

> Smooth the PWM output with an RC and feed a current
> source (BD139 or similar with R in emitter-to-ground).

I'll do some tests.....

Thanks, Rob.

--
Rob Hamerling, Vianen, NL (http://www.robh.nl/)

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