Speed Reduction for a DC Motor

Discussion in 'The Projects Forum' started by jj_alukkas, Nov 9, 2011.

  1. jj_alukkas

    Thread Starter Well-Known Member

    Jan 8, 2009
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    I have a Car Radiator Fan motor for 12v DC, 2-wire and pulls 1.5A when unloaded to something near 6A when loaded. I am using it for another project and need to reduce the speed by half. It need not be variable, just a one step reduction to near half the normal speed. Any simple tricks to do it? Can use FET's or anything, but I would prefer to have it built for 10A load. I searched and found only PWM driven variable models, which would not be of much use for my application. How to go with this?
     
  2. SgtWookie

    Expert

    Jul 17, 2007
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    What is your application?
     
  3. iONic

    AAC Fanatic!

    Nov 16, 2007
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    Actually PWM is a very efficient way to get your fan down to half speed. With a fixed Duty-Cycle of 50% you will have the fan at half speed.

    Waiting to see what your application is though.
     
    Last edited: Nov 9, 2011
  4. jj_alukkas

    Thread Starter Well-Known Member

    Jan 8, 2009
    751
    5
    Its kind of a light polishing equipment, direct drive, doesnt need much torque.
     
  5. jj_alukkas

    Thread Starter Well-Known Member

    Jan 8, 2009
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    So I guess for the simplest pwm, I would need a 555 driving an FET or power transistor?
     
  6. SgtWookie

    Expert

    Jul 17, 2007
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    That's basically it, but you will also need a large diode across the motor; or the current going through the motor will have noplace to go when the MOSFET turns off, and it will blast its' way through the MOSFET, killing it.

    The diode should be rated for at least as much current as you expect to have going through the motor.
     
  7. THE_RB

    AAC Fanatic!

    Feb 11, 2008
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    There are a lot of cheap kits on the market for "DC motor PWM speed controller" you might want to do a google and just buy a $20 kit that will be easy to assemble and reliable.
     
  8. jj_alukkas

    Thread Starter Well-Known Member

    Jan 8, 2009
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    I prefer building one. Ordering takes a lot of time and money. Will do it the MOSFET way. Thank you all!
     
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