Working of Universal Motor:
A universal motor works on either DC or single phase AC supply. When the universal motor is fed with a DC supply, it works as a DC series motor. When current flows in the field winding, it produces an electromagnetic field. The same current also flows through the armature conductors. According to basic motor principle, when a current carrying conductor is placed in the magnetic field, it experiences a mechanical force. Thus mechanical force is exerted on the current carrying armature conductors and torque is produced on rotor. Therefore the rotor starts to rotate.
When fed with AC supply, it still produces unidirectional torque. Because armature winding and field winding are connected in series, they carry same current. Hence, as polarity of AC voltage changes and current reverses its direction, the direction of current in armature conductors and magnetic field in the air-gap reverses at the same time. The direction of magnetic field and the direction of armature current reverse in such a way that the direction of force experienced by armature conductors remains same. Thus unidirectional torque is produced and motor continues to run in the same direction. Thus, regardless of AC or DC supply, universal motor works on the same principle as that of DC series motor. Since motor works on both the type of supply: AC or DC, it is referred as Universal motor.
Applications of Universal Motor: 1) Mixer and Food processor 2) Heavy duty machine tools 3) Grinder 4) Vacuum cleaners 5) Drills 6) Sewing machines 7) Electric Shavers 8) Hair dryers 9) Cloth washing machine