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DC Electric Motor

  1. Apr 30, 2009 #1
    I am trying to make a simple electric (DC) motor using a battery (9V), wire, and magnet. For some reason the coil isn't spinning though. I scraped the entire insulation off one side, and half of the insulation off the other. Why isn't it working?
  2. jcsd
  3. Apr 30, 2009 #2
    Is it moving at all? Did you give it a kick start? Can you show us on youtube?
  4. Apr 30, 2009 #3
    Last edited by a moderator: Apr 24, 2017
  5. Apr 30, 2009 #4
    Well, sometimes it spins and sometimes it doesn't! I don't really know what's going on...
    If it spins for too long, does it drain the battery?
  6. Apr 30, 2009 #5
    I assume you are using a permanent magnet as the stator, and a dipole coil spining on an axle. You need to have a commutator on the axle so the current in the diplole coil changes twice per turn. The battery you use should be a 1.5 volt C or D cell. If possible, wind the battery wire about 5 turns around a compass in series with the motor to make sure current is flowing.
  7. Apr 30, 2009 #6
    i'm using sandpaper take off the insulation on half of the wire on one side, and all the insulation off on the other side; doesn't this work as a commutator?
  8. Apr 30, 2009 #7
    I have built a motor like yours. You have to make sure the current is flowing when the battery leads are both touching the commutator.
    Also, the torque on the rotor is maximum when the dipole is at right angles to the magnetic field.
  9. May 2, 2009 #8
    Are you sure the batteries are fresh? Try changing batteries and see if the execution improves. I've had it happen to me once, the apparatus was all perfect and I set up everything according to instructions...then I found out the batteries were half dead.
  10. May 3, 2009 #9
    it works with a large magnet, but not with a small one. What do I have to change so that it works with the small one?
  11. May 3, 2009 #10


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    It is very hard to give advise without knowing exactly what you have. Can you post a pic?
  12. May 3, 2009 #11
  13. May 3, 2009 #12
    Looking at the teachingphysics jpg, this motor works on the principle that current flows through the coil during less than half a turn, when it makes electrical contact with the heavy wire. All of the insulation should be cleaned off both ends of the small (coil) wire to ensure this. The motor also operates because the coil is slightly unbalanced so that the coil breaks contact with the heavy wire while it spins. Make sure that when the spinning coil comes to rest, the coil itself is vertical (lile this "l") and not like this( "--"). From the side, it should look like "--O--" and not "----". In motor terms, the magnetic axis of the spinning coil should be horizontal when it is conducting electricity.
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