Variable speed DC motor circuit

Discussion in 'General Electronics Chat' started by sberesfo, Dec 21, 2008.

  1. sberesfo

    Thread Starter New Member

    Dec 21, 2008
    2
    0
    Please see attached diagram of a simple motor circuit.
    1. How do I determine the best value of R1 to achieve maximum control of the motor speed?
    2. Is there any drain on the battery when R1 is off (motor stopped)?
    3. Any minor modifications to enhance the circuit or to make it more efficient?
    Thank you for any feedback on my post!!
    Scott
     
  2. hgmjr

    Moderator

    Jan 28, 2005
    9,030
    214
    There is an inherent problem with using resistance to control the speed of a dc motor.

    The problem arises when the motor is loaded. As the load to the motor increases, it draws more current from the power source. With a resistance in the power line, the voltage drop across the resistor increases. As the voltage increases across the resistor, the voltage available to drive the motor decreases. The motor then tends to stall easily because it cannot deliver the torque needed to handle significant mechanical loading of the motor.

    What you need to look at is the technique called PWM which stands for pulse-width modulation.

    hgmjr
     
  3. sberesfo

    Thread Starter New Member

    Dec 21, 2008
    2
    0
    hgmjr
    Thank you very much for pointing me in the right direction. I knew that circuit was too simple to be efficient. Thanks again!
    Scott
     
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