Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Built an electric motor but missed something

  1. Jan 7, 2016 #1
    Hello!
    I haven't read all that much about electrical engineering in school yet but I decided to build an electric motor since I enjoy doing this stuff. The problem is that when I connect it to an 11.1V battery that I had lying around, it just spazzes a little bit but it won't turn. I'm also guessing the amp draw is very high since the copper wire (coil) is 1.4mm in diameter (because if the resistance is low the amp draw must be higher, right?), and the cables got hot and there were sparks.

    If you look at the picture you can see that I'm using small neodymium magnets which I suppose should be fine(?)
    I know the construction might look ridiculous to you but it's my first time ever building something like this so be gentle.

    Anyways, do I need to buy resistors to make this work or is there anything else I did wrong? (or even buy thinner wire which makes the resistance higher)
    Is there a special way to do the winding of the wire?
    The axle is supported by bearings so the magnets should be able to push it around i think.
    (And let's not forget that english isn't my first language so let me know if I was unclear)

    Picture: https://gyazo.com/593d9bcf7a51f12e0f9fc31434d0a80a

    Thanks in advance! :)
     
  2. jcsd
  3. Jan 7, 2016 #2

    russ_watters

    User Avatar

    Staff: Mentor

    What happens if you give it a little push?
     
  4. Jan 7, 2016 #3

    berkeman

    User Avatar

    Staff: Mentor

    Welcome to the PF.

    I would recommend against using a big battery for your power supply for your first projects. The consequences of a mistake can be pretty bad (burst battery, acid all over the place, fire, burns, etc.).

    A much better choice would just be a 12Vdc, 1A or 2A power supply "brick". You can pick them up pretty cheaply at Radio Shacks or other similar stores (or online). Can you get one of those?
     
  5. Jan 7, 2016 #4
    Should I power it from the wall? I actually found one 12Vdc 1.5A power supply that isn't being used. Should I give that a go?

    Edit: @russ_watters I'm not sure if I want to try it again with that battery because of the heat and sparks :/
     
  6. Jan 7, 2016 #5

    berkeman

    User Avatar

    Staff: Mentor

    Yes, that's a much better choice.
    Good judgement on your part! With the wall-powered brick supply, you should be much safer in this project.

    Can you post more diagrams of how you wound it, and how you made the commutator? Russ' suggestion of a light push is a good one, especially if your commutator has moderate gaps. :smile:
     
  7. Jan 7, 2016 #6

    berkeman

    User Avatar

    Staff: Mentor

    BTW, don't ask me how I know this... o0)
     
  8. Jan 7, 2016 #7

    meBigGuy

    User Avatar
    Gold Member

    Are the coils correctly connected? What happens if you reverse one coil? Or turn one magnet around? You will need to give it a spin, and try both directions.

    You can follow the directions here:
    http://holbert.faculty.asu.edu/wise/dcmotor.htm
     
  9. Jan 8, 2016 #8
    Tried to be accurate but.. https://gyazo.com/68c9c0337ec3c4b49474ba21cddd1e93
    I don't know exactly how the "brick" converters work but can the amp draw not exceed 1.5 amps if it says so on the back of the power supply?

    Will definitly try this if the power supply doesn't solve the problem :)
     
  10. Jan 8, 2016 #9

    sophiecentaur

    User Avatar
    Science Advisor
    Gold Member

    I guess you have the scars to prove it?
     
  11. Jan 8, 2016 #10

    sophiecentaur

    User Avatar
    Science Advisor
    Gold Member

    That sounds like the answer - there are several combinations that won't work (or just work badly) - so go through the combinations systematically. The magnets should be NS-NS (or the reverse). IF you are getting sparks then you don't need to worry about the continuity of your wiring. The sense of the coil wiring is that the windings should both be clockwise or anticlockwise so that the whole length of coil is wound like a solenoid.
    Sorry to ask and don't be offended, William, but is the wire enamelled (i.e. with insulating lacquer around it)? Several threads on this sort of topic have revealed that the OP is using plain copper wire, which is just a short circuit.
     
  12. Jan 8, 2016 #11
    Yep it's enamelled (polyurethane). I'm going to try the power supply first though since the amp draw from the battery is high whether the axle is turning or not.
     
  13. Jan 8, 2016 #12

    sophiecentaur

    User Avatar
    Science Advisor
    Gold Member

    If trying all the combinations does no good (and you have checked for shorts) then your wire length may be too short. Using twice the length of wire with half the cross section could reduce the current draw and motor will still turn. Do you have access to a Multimeter, to measure the current?
     
  14. Jan 8, 2016 #13
    I tried the 12Vdc 1.5A power supply but it still spazzes like every half second, similar to the first attempt. Current should be passing through though since I was able to get a piece of metal stuck on both sides of the metal core (correct me if I'm wrong), although it was a bit weak imo. Should I try turning the magnets first and then redo the winding if turning the magnets doesn't work? Should I reverse one coil as meBigGuy said?

    Edit: I should probably mention that the "spazz" is more like a pulse, sometimes it's strong and sometimes it's weaker. I don't know if this is because of the power supply or the winding. Probably the winding since it acted similarly when i used the battery.

    Edit 2: I removed the wooden pieces that supported the magnets and held the magnets in my hands instead, but it didn't really matter which way I held them, it acted strange and I could feel the pulse with my fingers :S Probably going to have to try a different winding.
     
    Last edited: Jan 8, 2016
  15. Jan 8, 2016 #14

    sophiecentaur

    User Avatar
    Science Advisor
    Gold Member

    That could help or . . . . Make the easiest change first. Real motors have iron cores in the armature so your coils are pretty weak electromagnets. What do you get when you put one of the magnets against one of the coils - on the table, connected directly and not on the motor? If you get no significant force that way then the motor won't go. My guess is that there are just not enough turns on the coils. If the coil magnet test works then I would suspect your wiring. Is it soldered well?
     
  16. Jan 8, 2016 #15
    I don't understand. If i put a magnet against the coil it stays there and the force is pretty strong. Could you draw?
     
  17. Jan 8, 2016 #16
    Now that I'm looking at the picture on the web page that @meBigGuy linked to I see that we have done the winding differently. I will try changing it later.
     
  18. Jan 8, 2016 #17

    berkeman

    User Avatar

    Staff: Mentor

    More like scares, fortunately. I was very lucky several times... :rolleyes:
     
  19. Jan 8, 2016 #18

    sophiecentaur

    User Avatar
    Science Advisor
    Gold Member

    OK. That's what I meant. If there is that much force between one magnet and one coil then there should be plenty to turn the motor. If the coils aren't being pulled to line up with the magnets then it looks as if one is pulling and one is pushing ??
    Another point, though, have you got the phase of the commutator right? It should change the direction of the flow at the angle when the coils are just going past the magnets. That way, once the magnet has done its attracting job, it then starts to repel.
     
  20. Jan 8, 2016 #19
    I tried winding it the way the picture was showing this time, but I'm still getting the pulse-thing (the thing is I'm not really feeling a repelling force, It's just attracting alot, then it attracts less, and sometimes the frequency of this "pulse" goes wild). I'm beginning to think that I should redesign the brushes since the current might be getting interrupted.
    As for the commutator, I think it is correct. The "gap" is in line with the coils i guess you could say.
    Thank you for sticking with me btw :)
     
  21. Jan 8, 2016 #20

    sophiecentaur

    User Avatar
    Science Advisor
    Gold Member

    Is it possible that the gaps, on either side (or the brushes) are not 180° separated and that both brushes happen to be contacting the same segment of the commutator? That would be be a short.
    These suggestions of mine are what I would be looking for in my first 30 seconds of looking at the thing in real life. I am convinced that there's something really simple going on here. You are not permitted to give up now, :wink:
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?
Draft saved Draft deleted



Similar Discussions: Built an electric motor but missed something
  1. Electrical motors (Replies: 1)

  2. Electric Motors (Replies: 3)

  3. Electric Motor (Replies: 12)

Loading...