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On demand 12V fan control

Discussion in 'Electronic Repair' started by N_Cook, Mar 28, 2012.

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  1. N_Cook

    N_Cook Guest

    Under therrmistor control. If at power up the DC voltage is too low to start
    the fan can you always rely on the fan starting at some point with a slowly
    increasing voltage or does it depend on the make/design of fan ?
  2. Franc Zabkar

    Franc Zabkar Guest

    FWIW, here is an article that shows the innards of a typical
    thermistor controlled CPU fan:

    - Franc Zabkar
  3. amdx

    amdx Guest

    Different fans will start at different voltages.

    Your circuit is NOT a thermistor and a fan in series, right?
  4. Phil Allison

    Phil Allison Guest

    "Gareth Magennis"

    ** A great many power amplifiers have the same kind of circuit.

    BLDC fans start reliably when the applied DC voltage is about 33% of
    ated - no matter how slowly the voltage rises.

    IOW there is no need for a kick start.

    .... Phil
  5. N_Cook

    N_Cook Guest

    3 fans fed from the same varying supply. 2 large , one small, all nominally
    12V. The 2 large start with the applied "cold" voltage and eventually the
    small one starts with warming of the amp . Checked by slowly powering from
    a bench ps a few tmes . But I randomly picked up another new fan that I had
    about and once out of 10 or so times it did not start by the time it had
    reached 12V. I decided as this amp was never used for low power use that I
    would disable the ramping and set it on maximum drive always, not worth the
    risk/inconvenience of stressed components/mid-performance chance of a cut
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