12v dc motor speed self limited?

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SUMMARY

The discussion centers on the behavior of a PM brushed DC 12V fan motor, specifically regarding its voltage intake and performance under load conditions. The motor operates at approximately 90 watts, with a PWM power source rated for 12-24V and 50 amps. Users report voltage readings of 16.5V in the pushing direction and 13.5V in the pulling direction, both drawing around 10 amps. The conversation concludes that DC motors exhibit a form of self-limiting voltage intake due to the resistance of the magnet wire, which increases with temperature, affecting performance and potential overheating.

PREREQUISITES
  • Understanding of PM brushed DC motor specifications
  • Knowledge of PWM (Pulse Width Modulation) power sources
  • Familiarity with electrical resistance and its impact on motor performance
  • Basic principles of wattage and current calculations in electrical systems
NEXT STEPS
  • Research the thermal characteristics of PM brushed DC motors
  • Learn about PWM control techniques for optimizing motor speed
  • Investigate the relationship between voltage, current, and wattage in electrical circuits
  • Explore methods for measuring and managing motor temperature to prevent overheating
USEFUL FOR

This discussion is beneficial for mechanical engineers, electrical engineers, and hobbyists working with DC motors, particularly those interested in optimizing motor performance and understanding electrical characteristics in automotive applications.

moroeder
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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.

Max
 
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Welcome to Physics Forums moroeder.

moroeder said:
...do these DC motors have self limiting voltage intake based on their wattage?...

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.

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http://hyperphysics.phy-astr.gsu.edu/hbase/electric/elepow.html"
 
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