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PWM for noiseless cooling fan

Discussion in 'Electronic Design' started by [email protected], Jun 1, 2005.

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  1. Guest

    PWM for noiseless cooling fan

    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.

    0 is a zero
  2. Ian Stirling

    Ian Stirling Guest (or similar in your country).
    Purchase a variable speed cooling fan, for several pounds/..., add a variable
    resistor to the speed control input, and job done.
    I also found (from ebuyer) that the 60p 12cm fans run absolutely noiselessly
    and start reliably on 3.3V
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