1. Welcome to our site! Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.
    Dismiss Notice

I need to vary speed of 9V motor...

Discussion in 'Electronic Projects Design/Ideas/Reviews' started by impjester, Oct 7, 2002.

  1. impjester

    impjester New Member

    Joined:
    Oct 7, 2002
    Messages:
    2
    Likes:
    0
    I have a 9V motor. I need to be able to adjust the speed of the motor, from 0 volts to the 9V max. I have my 9V battery attached to the motor via alligator clips for now.

    I know a potentiometer will work, but I've already burned one out messing around...lol. I can't seem to find a pot that fits my scenario...and the Radio Shack people are of little help. (I also tried a dimmer switch from a ceiling fan, but got no current at all through that.)

    I'm kinda new to electronic components, so I don't even know what the specs on the pot meant:

    250VDC
    power rating of .25W
    100K Ohm resistance

    Anyone have any ideas? Can I build my own? HELP! :(

    Thanks!

    Keith (impjester@hotmail.com)
     
  2. pebe

    pebe Member

    Joined:
    Sep 24, 2002
    Messages:
    354
    Likes:
    1
    Location:
    Ellon - Scotland
  3. thec

    thec New Member

    Joined:
    Sep 30, 2002
    Messages:
    40
    Likes:
    0
    Location:
    Alvesta, Sweden
    Although the answer is posted, I could explain why you messed up with the potentiometer :)

    The little motor you're running, are using too much current for the potentiometer to handle. I'll explain.

    The pot can handle 250VDC (Volts, Direct Current), which is plenty enough. Since you're running 9V (I guess DC), it's no problem.

    The problem is the 0.25W limit. Look at it this way. A basic forumla in electronics world say that V*A = W ... if you put in your specs there, you'll get 9V * A = 0.25W, divide both sides with 9, and you'll get A = 0.25/9 = ~28mA.
    Now. That means you can run an engine whích uses MAXIMUM 27mA at 9V (because of the potentiometer of course). If the engine doesn't have it printed, you could measure it up with a digital meter in serial with the engine and a battery/power supply.

    I doubt the engine runs that cheap, hence, you're using too much power for the potentiometer to handle, and you get some smoke coming out from it. :)

    Solution : get a more robust potentiometer (will cost you more and you have to measure just how robust you'll need) or build the clever schematics pebe posted (nice/better solution).

    Hope you learned something... that's what we're here for.
    //Albert "thec" Sandberg
     
  4. dave

    Dave New Member

    Joined:
    Jan 12, 1997
    Messages:
    -
    Likes:
    0


     
  5. impjester

    impjester New Member

    Joined:
    Oct 7, 2002
    Messages:
    2
    Likes:
    0

    Wow......how you explained it really helped me a lot. I guess I just need to calculate exactly what I need....although I'm unsure whether those unknown values for the motor are printed on the box or housing. I'll look into that.

    As for that schematic.....I'm scared.

    <sigh>

    Thanks though! I may get this working yet.

    Keith
     

Share This Page