What is the working principle of a DC motor?

Short Answer:

The working principle of a DC motor is based on the interaction between a magnetic field and an electric current. When current flows through a conductor placed inside a magnetic field, it experiences a mechanical force that causes it to move. This force produces rotation, which is used to do mechanical work.

In a DC motor, the current is supplied to the armature winding, which is placed in a magnetic field created by either permanent magnets or electromagnets. Due to the Lorentz force, the armature starts rotating. A commutator is used to reverse the direction of current in the coil, maintaining continuous rotation.

Detailed Explanation:

Working principle of a DC motor

A DC (Direct Current) motor works on a simple but powerful principle from physics: “When a current-carrying conductor is placed in a magnetic field, it experiences a force.” This is known as the Lorentz Force. This principle is the foundation behind how electrical energy is converted into mechanical energy in a DC motor.

When direct current is supplied to a DC motor, it flows into the armature winding (coil). The armature is located between the poles of a magnet or electromagnet, which provides the magnetic field. According to Fleming’s Left-Hand Rule, if the thumb, forefinger, and middle finger of the left hand are held at right angles to each other—

  • the forefinger shows the direction of the magnetic field (from north to south),
  • the middle finger shows the direction of current (from positive to negative),
  • then the thumb will point in the direction of the force or motion.

In the motor, the current flows through the armature conductors. Since the armature is placed in a magnetic field, each conductor experiences a force. These forces are opposite in direction on opposite sides of the coil, which causes the coil to rotate. This continuous rotation of the armature is the mechanical output of the motor.

But one more important thing must happen: the direction of the current in the armature must reverse after every half rotation. If it didn’t, the armature would stop after turning 180 degrees. This is where the commutator comes in. The commutator is a split ring that reverses the direction of current in the coil every half rotation, allowing the armature to keep spinning in the same direction.

A simple DC motor has these essential parts:

  • Stator: Provides the magnetic field using permanent magnets or field windings.
  • Rotor or Armature: The rotating part where the current flows.
  • Commutator: A mechanical switch that reverses the current direction.
  • Brushes: Maintain contact with the commutator to supply current to the armature.
  • Power supply: A DC voltage source that feeds the motor.

Once the motor starts rotating, it produces a back EMF (electromotive force) in the opposite direction of the applied voltage. This back EMF increases with speed and reduces the net voltage across the armature. This is nature’s way of automatically limiting the current and protecting the motor from damage.

DC motors are commonly used in toys, small appliances, electric vehicles, and industrial machines because of their easy speed control and smooth starting torque.

Conclusion:

The working principle of a DC motor is based on electromagnetic force. When current flows through a conductor placed in a magnetic field, it experiences a force that results in rotation. A commutator ensures that the direction of the current changes correctly to keep the motor spinning. This simple yet powerful concept is what makes DC motors essential in many real-world electrical applications.