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Fan control with pwm

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mgeno216

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So I want to control a fan with pwm. i am going to use a 555 timer to accomplish that. The fan responds to the average voltage right? So 7v at 70% duty= 4.9v. What is the minimum hz that this will work because obviously I can't have a circut with .0001 hz.

Mike
 
What type of fan motor is it? What is the motor voltage? What is the supply voltage?

Typically PMW frequencies of a few hundred to several thousand Hertz are used.
 
It is a fan for an xbox 360. It has a DC brushless motor, good up to 12v and draws .4 amps per fan. There are two fans that I want to control each with the same specs

Mike
 
The fan specs are fine? I just want to verify that multiplying the duty cycle by the supply is correct way in determining what speed the fan will operate at?

Mike
 
You can check the fan speed versus voltage by testing them with a variable DC power supply. But I understand that some brushless motors may not work properly with PWM, so you would have to experiment with that.

If there is a problem, then you could run the PWM signal through a large inductor to smooth the PWM signal into DC. The higher the PWM frequency, the smaller the required inductor.

The duty-cycle of the PMW does determine the average output voltage. Just multiple the duty-cycle by the input voltage, as you did.
 
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