Rotary Potentiometer Sizing

Discussion in 'General Electronics Chat' started by, Aug 6, 2014.


    Thread Starter New Member

    Aug 6, 2014
    Have a Class 2 transformer:
    Input: 120V 60Hz 25W
    Output: 12VDC 1000mA

    And a DC brushless fan rated at:
    DV12V 0.48A

    For this project I would like to use a on/off rotary potentiometer to adjust the fan speed from off to barely moving to fast (wide open) over the range of the potentiometer with out over loading the fan or power supply. Can someone give a me suggested ohm rating that I should use on the potentiometer? If the components that I have selected are not correct for my project please feel free to suggest different components that would be better suited.

    Thanks in advance for your help,

  2. bertus


    Apr 5, 2008

    Regulating the speed with a potentiometer is not very smart.
    You would need a powerfull potentiometer, that will burn the not used power.
    A PWM regulation will be more efficient.
    SgtWookie has a nice project for it:
    Project: Simple PWM circuit
    The fan can be placed on the position of the load in the schematic.
    As a fan is an inductive load, a back EMF diode will be needed.


    PS Don't use your email-adresses as user name
  3. inwo

    Well-Known Member

    Nov 7, 2013
    Just for an (bad) example:
    And about $50
    Rheostats are rated in amps.


    225 Ohm

    Rheostat, 225 ohm, 0.47 amp, 50 watt, 1/4" x 1/8" slotted shaft with locking nut. Type R50. 2-3/8" diameter body x 1-1/2".

    Search for surplus rheostat

    Go with the PWM.