Brush DC Motors

The Brush DC motors use commutators and carbon brushes to apply current through the windings as the motor rotates. The Brush DC motor utilizes wound elements in the rotor and permanent magnets attached to a stationary stator ring. In a Brush DC motor, electrically separated motor windings are connected to the commutator ring. Current is carried by spring loaded brushes, through the commutator into the windings of the rotor. The current in the windings creates magnetic fields, which react with the statorís permanent magnetic field. The magnetic repulsion causes the rotor to rotate. This rotation causes the brushes to make and break connections through the commutator with different winding pairs. The moving magnetic field provides the torque necessary to rotate the motorís armature.



  • Low cost
  • Simplicity
  • Availability


  • Brush dust
  • Brush to commutator arcing and wear
  • Electromagnetic interference
  • Mechanical noise
  • Short motor life
  • Low efficiency
  • Limited speed
  • Poor thermal characteristics in vacuum

Electrical Time Constant

For DC motors this is the ratio of electrical inductance to armature resistance.

See also: AC Induction Motors, Brushless DC Motors, Electric Motors, Stepper Motors.

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Subjects: Electrical Engineering