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12v dc motor speed self limited?

  1. Nov 17, 2011 #1
    Fellow Engineering Lovers,

    Being a mechanical with limited electrical I must turn to the electron masters for answers. I have a PM brushed DC 12 V fan motor on of a standard electric cooling fan on a car radiator. My calculation comes out to be about 90 watt. I also have PWM 12-24 power source 50 amp that appears to work properly. However the fan in the pushing air direction will only swallow 16.5 volts. In the puller direction 13.5 volts with both at about 10 amps.

    I am running the controller on the 24 volt input and with no load I have about 26 volts. The PWM is a very robust piece out of our US military equipment. No heat to speak of and you can certainly tell when the system is turned on because of draw down of the other equipment running in the car. I have an air cooled engine and want to move more air over it by spinning the fan blade faster. Sounds good but don't have any idea if it will work.

    Finally my question is, "do these DC motors have self limiting voltage intake based on their wattage?" Sounds crazy but what I am seeing seems like it could be so. Please help a mechanical feel the electrons in a more favorable fashion. And if you can steer me in the right direction that would be good too.

  2. jcsd
  3. Nov 17, 2011 #2


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    Gold Member

    Welcome to Physics Forums moroeder.

    Yes, so to speak. The magnet wire used to wind the magnets has resistance which will rise depending on its temperature. So the wattage of the motor tells you how much current and voltage you can supply without overheating it until failure.


    http://hyperphysics.phy-astr.gsu.edu/hbase/electric/elepow.html" [Broken]
    Last edited by a moderator: May 5, 2017
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