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CPU Fan Mod Help

Discussion in 'Misc Electronics' started by Don B, Jul 4, 2003.

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  1. Don B

    Don B Guest

    I currently have an Athlon XP computer system. This system is great with
    the exception of the CPU fan. There are two major problems with it, it is
    very noisy and the "pitch" of the fan often changes, I suspect this is due
    largely to slight voltage fluctuations.

    The fan is rated at 12V, .16A and 1.92W Min voltage is 7V

    What I'd like to do is drop the voltage a little, say to about 9.5-10v and
    add a capacitor to the line to smooth out the voltage.

    If I understand V=IR correctly, I need a 150 Ohms 1/2 W resistor to do the
    voltage drop. Can someone confirm this?

    What I do not know is how to select a capacitor to quite the line. I
    suspect I need something pretty small, but again I have no idea how to
    calculate the value.

    Thanks for any input.

    PS: I am aware to dropping the voltage on the CPU fan will reduce cooling
    efficiency. I'm not really worried about it.
  2. cpemma

    cpemma Guest

    The fan impedance is 75R. So to reduce the voltage to 10v on a 12v supply,
    resistor if Ohm ruled would be 15R, not 150.

    However, most PC fans lose 300mV or so at the electronic commutation, and
    many include a reverse-polarity protection diode, so of the 12v supply, the
    motor winding may see only 11v, so there are other considerations to take
    into consideration.

    But at the end of the day, it's hardly likely that voltage fluctuations are
    high enough to affect the fan noise but don't crash the computer - check the
    fan mounting screws and/or bearing wear.
  3. Brook Smith

    Brook Smith Guest

    From what you have said I am assuming your unit is using a 60mm fan. If you
    are using a retail heatsink and fan, this is EXTREMELY illadvised. The
    retail units are mearly adiquite as it is.

    I to would suggest that you look into a new heatsink and fan combo.

    The only reason I would see to do this is with higher RPM 80mm or larger
    fans, and then as it is a CPU fan, a variable approach should be used to
    ensure you get the results you want.
  4. N. Thornton

    N. Thornton Guest

    Or mount the existing fan on bits of rubber.

    Regards, NT
  5. Exactly. I don'e see why someone is dorking around with a defective
    fan, when fan/heatsink replacement are so inexpensively availalbe on
    eBay and from other sources. I personally go through from 1 to 2 CPU
    fans a year, and their replacement cost is typically $10 or less.

    Harry C.
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