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PWM Voltage for a Fan?

post #1 of 15
Thread Starter 
I am thinking of potentially making my own fan controller from parts I have laying around (essentially an arduino board). I plan to write a small windows GUI allowing me to control the fan speeds from my computer rather then using a dial.knob.
My question though is what Voltage is the PWM line for a standard case fan?
post #2 of 15
12v

And the leads are

Blue - Control 0.8v to 5.25 - (from t-ramp )
Yellow - Rmp speed (monitor)
Red - +12v
Black - 0v ground
Edited by andrewmchugh - 8/8/11 at 11:09am
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post #3 of 15
Thread Starter 
Does it have to be 12V, from my understanding PWM is due to the pulse width that the fan gets that controls the speed of the fan, however will this still work at say 5 or 9V?
post #4 of 15
I pulled up a PWM spec sheet and it says 5.25v maximum? I'll do a bit more reading...

http://www.formfactors.org/developer%5Cspecs%5C4_Wire_PWM_Spec.pdf
post #5 of 15
All board fan headers are 12V

page 9 in your pdf rampo
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post #6 of 15
He's referring to the actual PWM signal, not the fan power itself.
post #7 of 15
Quote:
Originally Posted by t-ramp;14508858 
He's referring to the actual PWM signal, not the fan power itself.

5.25 then ..
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post #8 of 15
Thread Starter 
That I am, I have no cares about the voltage in itself as the PWM controls how fast the fan is suppose to spin. According to this document http://www.formfactors.org/developer%5Cspecs%5CREV1_2_Public.pdf

PWM Control Input Signal
he following requirements are measured at the PWM (control) pin of the fan cable conne
WM Frequency: Target frequency 25 kHz, acceptable operational range 21 kHz to 28 kH
Maximum voltage for logic low: VIL = 0.8 V
bsolute maximum current sourced: Imax = 5 mA (short circuit current)
bsolute maximum voltage level: VMax = 5.25 V (open circuit voltage)

If this is true then I should be golden as the Arduino outputs 5V and has a max output current of 40mA (though I doubt it'll pull that much)
post #9 of 15
Ahh right U want to write a program to control the the 0.25 - 5.25 control line to control the speed of fans... sorry.. I didnt read the op at all I only looked at the title

I read

I am thinking of ....Voltage .... standard case fan?
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post #10 of 15
Thread Starter 
Yep, probably was a little misleading and I apologize for that.

I want to hook up my little arduino board with the PWM lines to the fans and control how fast they spin by writing two programs, one windows side and one arduino side, to allow me to do this. Its sort of a small proof of concept project to keep me busy once my fiancee gets a job and works different hours them myself.

Once I get that working, I could look into seeing if i can accurately read the RPM from the fans, though right now I could care less.
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