DC Motor Fundamentals: Connection, Components, and Characteristics

Posted on Feb 23, 2025 in Audiovisual Communication and Journalism

1. How is a DC motor made?

  • A DC motor comprises a stator and a rotor. In many DC motors, usually smaller ones, the stator uses magnets to create a magnetic field. In larger DC engines, this magnetic field is achieved with field excitation windings.

The rotor, the rotating component at the center of the motor, consists of coiled wire conductors. Current is supplied to the rotor through brushes, typically made of carbon.

Note: A coil is a wound length of conductive wire with a specific purpose within a motor.

2. In how many ways can you connect DC motors?

  • DC motors can be connected in three ways:

Motor_compuesto.jpg

Motor_paralelo.jpg

Motor_serie.jpg

Series, Parallel, and Compound Connections

3. What is the role of the commutator?

  • A commutator continuously transmits power, signals, or data from a stationary source to a rotating destination, or vice versa.

4. What is an inductor?

  • An inductor, or coil, is a passive electrical circuit component that stores energy in a magnetic field due to the phenomenon of inductance.

Components of an Inductor:

  • Winding Inductance: The set of coils that generate magnetic flux when electricity flows through them.
  • Yoke: A piece of ferromagnetic material, not surrounded by windings, designed to unite the poles of the machine.
  • Pole Piece: The part of the magnetic circuit located between the yoke and the air gap, including the core and pole shoe.
  • Core: The part of the magnetic circuit surrounded by the field winding.
  • Pole Shoe: The part of the pole piece near the armature and bordering the air gap.
  • Interpole (or Commutating Pole): A supplemental magnetic pole, with or without winding, used to improve commutation. Typically used in medium and large power machines.

5. Name three features of series, parallel, and compound DC motors.

Parallel:

  • The resistance of the main field winding is very high.
  • Suitable for applications requiring constant speed, regardless of adjustments, or where a significant speed range is needed.
  • The field winding is connected in parallel (shunt) with the circuit formed by the armature and auxiliary field windings.

Compound:

  • Excitation is provided by two independent field windings: one in series with the armature winding and one in shunt (parallel) with the circuit formed by the armature, series field winding, and auxiliary field windings.
  • They have a series field winding in addition to the shunt field winding. This series field, consisting of a few turns of thick wire, is connected in series with the armature and carries the armature current.
  • The series field flux varies directly with the armature current and is directly proportional to the load.

Series:

  • Runs at high speed when unloaded because the speed of a DC motor increases with decreasing field flux. In a series motor, this flux decreases with increasing speed, as the field current is the same as the armature current.
  • The power output is almost constant at any speed.
  • Largely unaffected by sudden voltage variations. An increase in voltage causes an increase in current, and therefore, the flux and back EMF, stabilizing the drawn current.