How to reduce PWM fan noise

[Elbert]

Here's a little tip that might be usefull for somebody..

I installed 3 small fans in the chassis of my amp, just to blow a puff of fresh air in case things get hot.

I bought a cheap and cheerfull tehermal fan-speed controll of e-bay just to minimize fan-noise under normal operating conditions.

Turned out this fan controll used pulse-width modulation, something that would cause the fnas to buzz excessively at low speed, or even stop an buzz even more at low temperatures.

I just soldered a 220uF cap parallel to the fans, and this reduced the problem considerably by smoothing out the PWM signal at low frequencies, thereby feeding the fans low voltage DC current in stead of pulses that were too widely spaced to allow tha fans to run smoothly.

 

[luka]

well...
I would increase the freq. instead (if that is what you hear), stress to the driver is high, charging capacitor fast.
If nothing else, I would use LC, not just C and get pretty much DC only.

Or have some minimum fan speed, so that they still turn

 

[random007]

If PWM noise is a problem, a much simpler solution is a variable resistor and a transistor. eg motor speed control by transistor : simple electronics

 

[Elbert]

That looks like a good approach, that will take care of the whole PWM noise problem!

The downside is of course tha this circuit dosen't have any temperature controll. But perhaps replacing the pot with a temperature dependendt resistor will take care of that?

 

[TechGuy]

If PWM noise is a problem, a much simpler solution is a variable resistor and a transistor. eg motor speed control by transistor : simple electronics

This limits the current flow to the fan and can cause the fan to stall. PWM is the method of choice for fan\motor speed control.

 

[random007]

If you can find them, Arctic Cooling have a rage of near-silent temperature controlled fans RRP $7US for 8cm (Arctic Cooling).

 

[Elbert]

Those arctic fans look nice, but unfortunately too large for my particular application.

True, stalling of the fan can be a problem, but what about using a trim-pot and a thermal resistor together? The pot can be used for setting the minimum idle speed above stall, and then the thermal resistor can run the show from there on?

 

[luka]

you sure can, yes