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Motor speed help

Discussion in 'Electronics Homework Help' started by Patrick Morrison, Mar 13, 2017.

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  1. Patrick Morrison

    Patrick Morrison

    2
    0
    Mar 13, 2017
    Hey,

    Complete novice to electronics here, and I was wondering if I could get some help. I'm trying to rig up a dc motor to a 9v battery and use a potentiometer to adjust its speed. I thought I calculated proper resistances, but so far I've either had a motor that didn't move, or pots that caught on fire. I measured the motor as drawing 62 miliamps, with of course 9v in the circuit, when there is no resistance.

    Any help would be appreciated!
     
  2. Minder

    Minder

    2,908
    609
    Apr 24, 2015
    A simple PWM controller designed around a 555 is a simple approach, there are many designs out there and $5.00 ones on ebay.
    M.
     
  3. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,258
    2,705
    Jan 21, 2010
    Motors are a type of load that is not easily controlled by a potentiometer. They require higher currents to start than the do to continue rotating. A resistor will limit this peak current far more than the operating current. This means that you may have trouble starting the motor. In addition, when in this state, most of the voltage appears across what may be a small section of the pot which will be called on to dissipate more energy than it is capable. At this point it lets out the smoke.

    All of this is to say that your experience with a pot is not at all unusual.

    Minder's solution is far better.
     
  4. Patrick Morrison

    Patrick Morrison

    2
    0
    Mar 13, 2017
    sorry, should have said that integrated circuits aren't allowed.
     
  5. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    Jan 21, 2010
    Please post your homework in the homework section.
     
  6. Audioguru

    Audioguru

    2,671
    605
    Sep 24, 2016
    We might not find anybody who remembers how it was done 55 years ago without integrated circuits.
    Can your teacher remember how it was done? Why doesn't your teacher teach how it is done today?
     
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