I am making a university graduation project which is a small electric toy car.
I used a DC motor, but I noticed that the brushes always spark when the car accelerates or starts to move. Also I am using a 24 V battery.
What should I do to fix this problem? Should I change the motor?

  • 3
    \$\begingroup\$ What makes you think that's abnormal? And is the motor rated for 24V? \$\endgroup\$
    – Passerby
    May 26 at 19:09
  • 4
    \$\begingroup\$ "the brushes always spark" That's usual. As you're in your final year you should be able to work out why switching the current through an inductive winding causes arcing (assuming you're an EE student). It's common to solder a disc ceramic capacitor directly across the motor terminals to reduce the resulting interference. If you need more suppression fit a pair of small inductors in the leads. A session on google should give you some typical values. \$\endgroup\$
    – Graham Nye
    May 26 at 19:26
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    \$\begingroup\$ All my simple radio controlled model airplanes use brushless motors because motors with brushes had the brushes wear out soon. The brushless motors last "forever". \$\endgroup\$
    – Audioguru
    May 26 at 23:07

1 Answer 1


The brushes in an electric motor will produce a certain amount of sparking at all times. When the motor is starting or the car is accelerating this will get worse.

Sparking is caused by the voltage on two adjacent commutator segments being different. The voltage on adjacent segments depends on the alignment of the magnetic field across the armature windings. At low load when there is little current in the armature the magnetic field runs across the armature from magnetic pole to magnetic pole giving little voltage between adjacent segments so little sparking.

As the load and hence armature current increases the armature produces its own field at right angles to the field produced by the main magnetic poles. This effectively rotates the overall field across the armature. This effect is known as armature reaction. The rotated field results in an increase in the voltage between adjacent segments resulting in sparking.


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