Author Topic: Fan PWM control using a signal generator.  (Read 2970 times)

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Offline drummerdimitriTopic starter

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Fan PWM control using a signal generator.
« on: May 14, 2019, 10:06:24 am »
I would like to control the speed of a fan by supplying it with 12V DC and using a PWM signal from my function generator to control its speed.

I have tried using a 25 KHz switching frequency and started at 30% duty cycle with 1V RMS but was not able to control the speed.

Should I connect my generator's ground to the black lead on the fan and the positive side to the blue cable?

Also, is it ok to leave the yellow (tach) cable unused?

 

Offline ogden

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Re: Fan PWM control using a signal generator.
« Reply #1 on: May 14, 2019, 10:10:17 am »
You can't put 1V RMS AC sine into 12V DC fan and expect it to rotate. Voltage is insufficient and fan will not like reverse voltage as well. Your signal generator shall supply 12V DC pulses.
 

Offline drummerdimitriTopic starter

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Re: Fan PWM control using a signal generator.
« Reply #2 on: May 14, 2019, 10:19:49 am »
You can't put 1V RMS AC sine into 12V DC fan and expect it to rotate. Voltage is insufficient and fan will not like reverse voltage as well. Your signal generator shall supply 12V DC pulses.

What is the purpose of the Blue PWM cable in that case if I only need the red and black ones for PWM?
 

Offline ogden

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Re: Fan PWM control using a signal generator.
« Reply #3 on: May 14, 2019, 10:24:32 am »
You can't put 1V RMS AC sine into 12V DC fan and expect it to rotate. Voltage is insufficient and fan will not like reverse voltage as well. Your signal generator shall supply 12V DC pulses.

What is the purpose of the Blue PWM cable in that case if I only need the red and black ones for PWM?

Third wire (in your case blue) is output signal from FAN - to measure fan speed (RPM). You shall PWM-modulate supply voltage of the fan, 12V (red wire).

[edit] As corrected later - you have 4-wire fan which means that blue wire is fan PWM control (logic) signal indeed.
« Last Edit: May 14, 2019, 02:40:38 pm by ogden »
 

Offline OM222O

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Re: Fan PWM control using a signal generator.
« Reply #4 on: May 14, 2019, 12:21:32 pm »
connect the output of the function generator to a BJT or a FET, which then drives the motor from a 12V supply. you're feeding it very little voltage at it's output!
 

Offline drummerdimitriTopic starter

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Re: Fan PWM control using a signal generator.
« Reply #5 on: May 14, 2019, 01:51:34 pm »
You can't put 1V RMS AC sine into 12V DC fan and expect it to rotate. Voltage is insufficient and fan will not like reverse voltage as well. Your signal generator shall supply 12V DC pulses.

What is the purpose of the Blue PWM cable in that case if I only need the red and black ones for PWM?

Third wire (in your case blue) is output signal from FAN - to measure fan speed (RPM). You shall PWM-modulate supply voltage of the fan, 12V (red wire).

You're incorrect.

Blue is for PWM signal and yellow wire is for tachometer (rpm reading). So if I only need the black and red leads so send a 12V PWM signal, what exactly does the blue wire do?
 

Offline ogden

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Re: Fan PWM control using a signal generator.
« Reply #6 on: May 14, 2019, 02:36:05 pm »
Blue is for PWM signal and yellow wire is for tachometer (rpm reading). So if I only need the black and red leads so send a 12V PWM signal, what exactly does the blue wire do?

Ups. Completely forgot about existence of 4-wire DC fans. Blue wire is PWM control indeed. It needs logical signal 5V or 3V. Thank you for correcting my  :bullshit:
 
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