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can someone idiot proof this simple circuit?

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Discussion in 'General Electronics Discussion' started by maark6000, Feb 8, 2012.

  1. Feb 8, 2012 #1
    maark6000

    maark6000

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    Feb 8, 2012
    I'm trying to build a device that will slowly turn a wheel, but I'd like it to be variable speed.

    So I bought a simple turntable motor (45RPM @ 24 Vdc, 60mA - operates at 12Vdc at 1/2 speed. Drive motor - Mabuchi RS-380SH. 1.1" diameter x 1.67". Gearbox - Molon #CHM-2435-1. 2.75" x 3.00" x 0.57" Threaded mounting holes in four corners. 5/16" diameter shaft, flatted and splined.)


    and I want to power it with a duracell 12V battery...

    but I'm thinking that in order to control the speed of the motor, I should do it using this circuit kit:

    http://www.electronickits.com/kit/complete/motor/ck1400.htm



    Is that right? Am I missing anything? doing anything dumb?

    Thanks!!!
     
  2. Feb 8, 2012 #2
    jackorocko

    jackorocko

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    Apr 4, 2010
    You could use a potential divider (potentiometer) and drop part of the voltage before it gets to the motor. That is by far the easiest route.

    Even if you dropped the full voltage across the resistor that is 12V * .06A = .72W
    That means a 1/2W linear potentiometer is all you would need and they come pretty cheap.

    Or you could use PWM as the module in your link does, which is more efficient. But that one in the link is overkill at 7A. You need 1/100th of that current.
     

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    Last edited: Feb 8, 2012
  3. Feb 8, 2012 #3
    maark6000

    maark6000

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    Feb 8, 2012
    Got it. Guess I was over concerned about what stresses would be put on the motor with just a potentiometer. So the circuit would simply be from battery to pot, pot to motor, and back to battery? Nothing else required?
     
  4. Feb 8, 2012 #4
    Resqueline

    Resqueline

    2,848
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    Jul 31, 2009
    I don't quite understand what's going on there.
    A Mabuchi RS-380SH is usually a 3-6V motor that has a mechanical shaft output of up to 40W. It also has a no-load electrical consumption of almost 5W.
    That doesn't quite rhyme with 24V & 60mA (= 1.44W).
     
  5. Feb 8, 2012 #5
    maark6000

    maark6000

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    Feb 8, 2012
  6. Feb 8, 2012 #6
    Resqueline

    Resqueline

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    Jul 31, 2009
    Ok, it says the same as you, but it's hard to read the motor label on the picture. It could be a special hi-volt wound version. Still strange about the wattage though.
    jacko's suggestion is cheap enough to try no matter what the outcome, but the PWM circuit should be bullet-proof no matter what.
     
  7. Feb 8, 2012 #7
    Sid723

    Sid723

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    Jan 28, 2010
  8. Feb 8, 2012 #8
    maark6000

    maark6000

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    Feb 8, 2012
    The label is even hard to read while holding it two feet in front of you.

    RS-380SH
    RD542/15 (although that slash could be a Y)
    made in china

    I think I'm going to get a 1/2 watt pot and a 3300 ohm resistor and go with that. I should point out that I will only be operating this circuit for very short periods of time... like 1 second, and then off. So I don't think heat or any other stresses will be an issue.

    Thanks so much everybody!!!
     
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