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More current and less voltage?

Discussion in 'General Electronics Discussion' started by trulytest, Sep 21, 2012.

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  1. trulytest


    Sep 5, 2012
    Ok, this may sound kinda stupid, but what will happen, if you instead of 12V and 90mA will add to device (cooling fan) 6V and 180mA?
  2. rob_croxford


    Aug 3, 2010
    The device will only draw as much current as it requires. So powering a 12V (90mA) device with 6V (180mA) will result in the device getting enough current but only half the voltage it requires.

    The ouput power of the supply remains the same, 1W or so

    Unless the device has a "negative resistace" charactersistic in which case the current must be limited using a ballast. For instance a ballast resistor to limit the current into an LED.
    Last edited: Sep 21, 2012
  3. shrtrnd


    Jan 15, 2010
    I work a lot of test and measurement equipment. I just wanted to add that the airflow
    is often critical inside precision equipment for cooling purposes, and your fan speed
    would change. If this is one of those critical applications, consider the cfm airflow requirements of your equipment.
  4. Merlin3189


    Aug 4, 2011
    Just in case you mean, what happens if you replace a 12V fan with a 6V fan, that's not a good idea, because the 6V fan will draw too much current from a 12V power supply. It will run faster, generate more noise and probably burn out quite quickly (if not immediately!)
    You can do the reverse, put a 12V fan in place of a 6V fan, but it will run at lower power and not deliver so much air.
    I have happily done this in a non-critical situation, replacing a 6V fan with a larger 12V fan, which ran more slowly and therefore much more quietly, but seemed to generate almost as much airflow and the cooling was adequate for my purpose.
    (I have often since thought that using larger slower fans would be a good idea. So many computers seem to use tiny fans running at high speeds, generating lots of noise and wearing out their bearings in a couple of years. But they are presumably constrained by space.)

    If you are replacing something like a CPU fan, you'd better stick to the same Voltage and at least the same size.
    Last edited: Sep 23, 2012
  5. BobK


    Jan 5, 2010
    And if what you mean is what would happen if I run a 12V fan at 6V, it would probably draw less current and run a lot slower, or possibly draw more current and not run at all.

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