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PWM Fan frequency and motor speed controllers

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BinaryBits:
So I have ordered a high flow Delta PWM fan which I want to try and build a fume extractor with. I have been looking at these cheap PWM speed controllers in order to regulate the speed of the fan, but most of them says that their frequency is 10 KHz, while the optimal frequency for the fan is I think around 25KHZ.

Would those 10KHz speed controllers work in order to adjust the fan speed between a 1-100% duty cycle, even though the PWM frequencies doesn't match exactly? And would there be any downsides to this? I think I read somewhere that the fan could make more noise because 10KHz is not outside what the human ear can hear?
I have also seen couple of speed controllers that says 100Khz, would that work, and maybe be better than the 10KHz ones?


Thanks in advance.

SuzyC:
You can control the speed of your fan without even using the PWM feedback output of a fan.

The easiest way to control speed is to control the voltage applied to the fan motor.

You must mind that there is a minimum voltage that the fan will start up and run at and you would have to limit the voltage controlling the fan to something above this voltage to start the span spinning. However, once the fan is started, you can usually decrease the fan motor voltage below the starting voltage for even slower fan speeds. Many CPU chassis-type cooling fans will start to operate at around 6-V and most can withstand voltages up to 14.6 volts without a problem.

You can can control fan speed if you generate a PWM output from a 555 timer or (best) from a MCU and any multi-KHz PWM frequency driving a fan motor will not be audible.

Then, if the PWM output is fed to a transistor or N-Channel MOSFET as a low-side driver(the fan is in series with the negative fan motor terminal and ground), then the PWM will directly control the fan motor voltage=speed, just by varying the PWM.  You may have to use a small capacitor across the motor to filter out spikes cause by the rapidly switching PWM signal to the motor.

BinaryBits:
Thanks for your answer. Yes I have read about the 555 timer, it seems one should be able to build a PWM controller with very few components, I think it was a 555, a diode, a resistor, a potentiometer, and a few capacitors?
Is the 555 suitable also for 12V fans, or would a 556 be better?

So whats the downside of controlling the fan with voltage, instead of PWM, more than that the fan cant be run with as low RPM?

Benta:
How about if you show us what fan we're talking about? Even a "røvsvensker" should be able to do that :)

charlie.n255:
If you switch a mosfet with the output of the 555 it should be fine to drive the fan.  :-+

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