PWM for noiseless cooling fan
sci.electronics.design
As summer is coming fast I do miss my expired old cooling fan lasted
10yrears and seems impossible to find an AC fan with continuous speed control in Europe. (if anybody has an idea...)
So my project for this weekend is to make a DC fan (from PC) diameter
90mm or 120mm. 12V with PWM.
I read a fair amount on the net and most posts here are about high current applications. I want to know if frequency of PWM is important to keep the fan noiseless. As it is the purpose of using PWM to keep rotation speed low. some quality PWM I found ready made use 25kHz: Q: would that frequency be a problem for a small PC cooling fan?
Furthermore, as I listen to SW radio, what about interference ?a metal box for the PWM would be enough to choke it? as I understand the DC motor runs quite smoothly its current (low pass LR).
Would it make sense to regulate speed both with lower voltage i.e. 7-8V instead of 12 and higher duty cycles? 40-50%? as I understand to start the rotor moving one needs about 20% Duty C. at nominal voltage (12V in this case).
One final issue is the capacitor parallel at the PWM input: is it always needed? what kind would be best suited to add on? I plan to use
2-mosfet circuit, and unregulated AC-DC cheapo radio shack supply. Eventually I would want to use it with batteries for traveling.
If you know of any online offering of this kind of circuit I'd appreciate it a lot.
A. @ artem0n yahoo.com @ 0 is a zero