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DC Motor Field Current Speed Control

  1. Jan 15, 2014 #1
    I have a Geared DC Motor rated 12V, 0.6A, 180RPM, 3kg.cm, 66% Efficiency. I measured the impedance of the disconnected motor at 45 Ohm.

    I want to use it with a with a simple 12V 1A DC Power Supply in a Field Current Control Circuit to be able to dial in variable speeds.

    Will the circuit in the attached diagram work?

    What are good Theoretical Resistance values to start with for R1 and the Potentiometer to give me a wide range of speeds with no load on the motor?

    For which Wattage should the Resistor and POT be rated to deal with the currents correctly?

    Thanks in advance!

    Attached Files:

  2. jcsd
  3. Jan 15, 2014 #2


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    That circuit won't do anything. The resistors are simply another load on the 12 volt supply.
  4. Jan 15, 2014 #3
    Yeah, I realised that. It could work if you limit your current at the power source, but that will over complicate things.

    I'm rather going with a simple 555 Pulse Width Modulation circuit...
  5. Jan 15, 2014 #4
    first of all yes for high amps a pot will be a waste of enrgy you have to use switches like transistors, the other thing the device needs to be in series with the motor , you circuit as you probably realized by now is in parallel with the motor so the motor would still go full speed.
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