Wiring a Potentiometer - what to get?

Discussion in 'The Projects Forum' started by Boston Roberts, Jan 17, 2015.

  1. Boston Roberts

    Thread Starter New Member

    Jan 17, 2015
    Hi all, absolute electronics newbie here needing some help. I want to wire up a potentiometer to a small DC electric motor. I want to be able to adjust the speed of the motor using the potentiometer. My power supply is 3v (two AA batteries) and my motor is a small DC electric motor that's either 1.5v or 3v.

    My question is, what type of potentiometer do I require for this project?

    Thanking you
  2. Reloadron

    Active Member

    Jan 15, 2015
    Controlling the speed of the motor using a pot (potentiometer) isn't a problem with a small DC motor. However, beyond the motors normal working voltage you also need to know the motors current requirements loaded, unloaded and in a stall. Controlling motor speed using a pot does work but isn't the best way to do it. However, for a newbie it's a good enough start without getting into more complex stuff. The type pot you need will depend on the motor's voltage and current ratings.

    For an overview you may want to give this a read:

    Scroll down to using a potentiometer as a rheostat. It's difficult to find good data sheets on these small cheap motors. I suggest you go to Radio Shack or similar and find yourself maybe a 25 Ohm 5 watt pot. Radio Shack sells a 3 watt which may work. Just depends on how much current your motor draws. Common data for these small cheap motors generally resembles this:

    • Further Details:
    • Rotation: Counterclockwise
    • Connections: Solder tab
    • Approximate weight: 17g

    • Specifications: (1.5VDC supply)
    • No load speed: 8,700 rpm
    • No load current: 320mA
    • Speed at maximum efficiency: 6,500 rpm
    • Current at maximum efficiency: 760mA
    • Torque at maximum efficiency: 6.2g-cm
    • Output at maximum efficiency: 410mW
    • Efficiency: 33.9%
    • Stall torque: 24g-cm

    • Specifications: (3VDC supply)
    • No load speed: 16,300 rpm
    • No load current: 380mA
    • Speed at maximum efficiency: 12,000 rpm
    • Current at maximum efficiency: 1.1A
    • Torque at maximum efficiency: 10g-cm
    • Output at maximum efficiency: 1.23W
    • Efficiency: 35.6%
    • Stall torque: 44g-cm
    Just do not take that as gospel.

    Last edited: Jan 17, 2015
  3. MrChips


    Oct 2, 2009
    This can be done with a pot for a small DC motor.
    Have you ever played with slot cars? The hand control used to control the speed of the car is a wire-wound pot wired as a resistor in series with the motor.

    What resistance and wattage to use?

    Let us take an example.
    Let us suppose the motor runs at 200mA @ 3V at no load.
    That represents a resistance of 3V/0.2A = 15Ω
    and a power consumption of 3V x 0.2A = 0.6W
    Hence if you wanted to cut the power to the motor by 50% you would use a 15Ω pot rated for 1W.

    Thus try a pot wired as a variable resistor, i.e. connect the center tap to one arm, of about 25Ω 1W wire-wound.
  4. Boston Roberts

    Thread Starter New Member

    Jan 17, 2015
    Fantastic! Thank you very much for all your help guys! Cheers!