Filtering PWM to clean DC at 75 watts?

Discussion in 'General Electronics Chat' started by magudaman, Feb 29, 2012.

  1. magudaman

    Thread Starter New Member

    Feb 27, 2012
    I am working on a micro controller to control two fans from a temperature probe. Basically I would like my heat sink remain at around 75C at all times but my fans would adjust in speed according to the load on the sink. These fans consume 36 watts each if not a little bit more and they really don't seem to like PWM power. In fact their data sheet says do not power them with PWM. Upon opening one up I see their is a decent sized capacitor inside that I am sure is taking the brunt of the PWM and would likely overheat.

    So I know on low power signal line stuff I have done a resistor capacitor network to create a low pass filter but I am not exactly sure how to scale that up.

    I can switch at around 50khz. My fans need 5.5v to 12V from a 12V source. They consume around 30.5w at full speed@12v.

    From my lab power supply I made this little chart

    Voltage Amps Watts
    5.2 0.28 1.456
    5.3 0.50 2.65
    5.4 0.57 3.078
    5.5 0.70 3.85
    5.6 1.08 6.048
    5.8 1.38 8.004
    6.0 1.54 9.24
    7.0 1.70 11.9
    8.0 2.00 16
    9.0 2.11 8.9
    10. 2.28 22.8
    11. 2.43 26.73
    12. 2.53 30.36
  2. magudaman

    Thread Starter New Member

    Feb 27, 2012
    Posted this in the wrong section, can a mod please delete this.