I am trying to build a simple DC motor for a project. I used a 9 V battery, 70 loops of copper wire, aluminum foil for the brushes of the commutator, and the commutator is wrapped by Aluminium foil and I used neodymium magnets with a pull of 16 Kg.

My motor worked for one minute and stopped and it is not working now anymore. What can be the potential problem that occurred?

enter image description here

(The copper wire has a thin layer of insulation, the brushes are touching the commutator, magnets are 6 cm close) Is it possible that a more powerful battery is required or can the brushes of the commutator be the problem? When the brushes are touching the commutator, I can feel that the motor vibrating but even if I try to give it a push it doesn't turn.

  • $\begingroup$ Give more info, photo, diagrams... $\endgroup$
    – peterh
    Commented Apr 19, 2017 at 1:22
  • $\begingroup$ If you can feel it torquing, have you tried lubricating the bearings or otherwise reducing friction? A bigger battery should help, but don't melt your wire with a 12V lorry battery. Another 9V might help. $\endgroup$
    – Paul Uszak
    Commented Apr 19, 2017 at 11:14
  • $\begingroup$ I checked the battery and it's fine. Is that the location of the brushes or should they be placed on top and bottom? $\endgroup$
    – CHA
    Commented Apr 19, 2017 at 11:45
  • $\begingroup$ My suggestion was to overcome the failings of the (you must admit) totally naff commutator and bearing construction. More power might create more impetus to maintain rotation against friction losses and the intermittent brush contacts. Honestly, I think that your 'economical' construction is probably beyond the limit of what could reliably work. $\endgroup$
    – Paul Uszak
    Commented Apr 20, 2017 at 13:04
  • $\begingroup$ another factor to consider is balance. On a good day this design will produce so little torque that it will not overcome even a small imbalance. It should spin absolutely smooth and free with no power applied. $\endgroup$
    – agentp
    Commented May 21, 2017 at 13:45

2 Answers 2


Read the battery datasheet. Those little 9 V consumer batteries with the snap on leads are not good for delivering this kind of power.

Measure the battery voltage when connected to your motor, and you will probably find it is close to 0. This may be the case even if the battery measures about right when open circuit.

Use a benchtop power supply. Something that can put out a few amps at 12 V should be good. Don't use a car battery because those aren't current-limited. If you cause a short, the car battery will deliver enough current to melt or explode something. A benchtop supply with current limiting at a couple of amps should provide enough power, but be safe when the inevitable short happens.

Added in response to picture

It is amazing that thing worked at all. Obvious problems:

  1. The large diameter of the commutator. Actually think about it. The brushes touching the commutator cause friction. The bigger the diameter, the lager the friction force due to higher speed, and that force is applied at a larger radius, so causes more torque. You want the commutator diameter to be as small as possible.

  2. Single coil rotor. This means there are two positions at which there is never any torque. This is when the plane of the coil is vertical in your picture.

  3. The spacing between the magnets. You want the magnetic field around the rotor to be as strong as possible. This means placing the magnets as close together as possible. They should be as close to the rotor without touching it as you can reliably manage. The bottom magnet can certainly be closer.

  4. The coil is a clear mismatch to the little toy battery you are trying to power this motor with. Use a bench power supply, as described above.

  • $\begingroup$ FWIW my son and I built a similar thing for his science fair and ran it off 4 AA's. The whole works was much smaller and lighter though. $\endgroup$
    – agentp
    Commented May 21, 2017 at 13:48
  • $\begingroup$ @age: 4 AAs have substantially more current capability and more available energy than one of this snap-on 9 V batteries. $\endgroup$ Commented May 21, 2017 at 16:17

Possibly poor contact at the commutator / brushes due to burning, loose or poor contact. But without more information that is only an educated guess.

  • $\begingroup$ @MrYouMath No, it offers a potential solution, so it's appropriate as a concise answer. $\endgroup$
    – Air
    Commented May 19, 2017 at 16:18

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