Universal Motor

A motor which can be operated on AC as well as on DC voltage is called universal motor. Single phase AC supply or DC supply is required for the operation of universal motor. The construction as well as working of universal motor is similar to DC series motor. Basically, the applications of universal motor founds in various field of engineering.


Basically, Universal motor has two main parts

  • Stator
  • Rotor


The stationary part of the machine is called the stator. The stator construction of universal motor is similar to single phase induction motors. It consists of the outer body, pole core, pole shoe and field winding. The pole core and pole shoe are made of laminated silicon steel. Lamination stampings are used to reduce eddy losses and silicon steel reduces hysteresis loss because the core of motor carries alternating flux. In case of DC motors, laminations are not necessary, but in case of universal motor, laminations are necessary because the flux is alternating in nature because the motor is operated on AC supply.

The field winding made of enameled copper is wound around the pole core and produce the required flux.


It is rotating part of the machine. It consists of shaft, armature and commutator. The Armature is made up of the stamping of silicon steel since it carries the magnetic flux slots are cut at its outer periphery of the armature and armature winding is placed in these slots.

The Armature is keyed to the shaft is a part of the rotor which transfers mechanical energy to the load.

The Commutator is also keyed to the shaft. The shaft is made of mild steel. Mechanical strength of mild steel is very high.

A compensating winding is used to reduce the reactance, voltage is present in the armature when universal motor operated on AC supply.

Working Principle of Universal Motor

The operation of universal motor based on the principle when a current carrying conductor placed in the magnetic field, a mechanical force is exerted on it and torque develops.

Operation or Working of Universal Motor

In universal motor armature winding and filed winding both are connected in series like DC series motors. This motor develops unidirectional torque whether it is connected on AC supply or DC supply.

universal motor

When single phase supply given to the motor, during the positive half cycle, current flows through the field winding and armature winding. The magnetic field is set up in both windings. The field of both windings is not aligned with each other. When rotor field tries to align itself with the main field an anti-clockwise torque is developed in the rotor.

When, the universal motor is connected to DC supply it behaves like a DC series motor.

The direction of rotation can be changed by interchanging connections to the field with respect to the armature as in a DC series motor.

Applications of Universal Motor

This motor is available in small sizes. This is invariably used in following appliances.

  • Vacuum cleaners
  • Electric hand drills
  • Mixer grinders
  • Domestic sewing machine etc.
  • Mixer and Juicer