Rotary Potentiometer Sizing

Discussion in 'General Electronics Chat' started by amberjack15@bellsouth.net, Aug 6, 2014.

  1. amberjack15@bellsouth.net

    Thread Starter New Member

    Aug 6, 2014
    1
    0
    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,

    Carl
     
  2. bertus

    Administrator

    Apr 5, 2008
    15,646
    2,345
    Hello,

    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.

    Bertus

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

    Well-Known Member

    Nov 7, 2013
    2,433
    315
    Just for an (bad) example:
    And about $50
    Rheostats are rated in amps.

    [​IMG]

    Rheostat
    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.
     
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