The universal motor can operate on both AC and DC power sources. When powered by DC, a constant magnetic field is produced, but with AC the field polarity changes with the current frequency. This causes the armature current direction and torque to also change to match the changing field. Universal motors have lower efficiency than DC motors due to losses, but they are compact and provide good torque for portable tools powered from AC mains. Laminated cores and increased conductor numbers help reduce losses and improve performance.

3. UNIVERSAL MOTOR
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4. Operation of Universal Motor
When DC supply given to the stator winding.
The field winding produced constant magnetic field.
The polarity of field remain same.
The field winding connected in series with the armature so that the same
current will flow in the armature.

5. Supply of AC Source
It produces variable magnetic field around the winding.
AC current have frequency so its polarity is changing with time.
The direction of current in armature winding determined according to
direction of field flux.
The polarity of field winding will change left side becomes south pole
and right hand side N- pole develop.
As the poles is changing the direction of magnetic field is also
changing. So the direction of current in armature winding is also
changing.
Direction of torque in both cases will be same.
The efficiency of smaller universal motor is around 30%, while the
larger universal motor have an efficiency of 70- 75%.

6. Drawback of Universal motor.
•The efficiency becomes low because of hysteresis and
eddy current losses.
•The power factor is low due to the large reactance of the
field and the armature windings.
•The sparking at the brushes is in excess.

7. Overcome of Drawback
•Thefieldcoreis madeupofthematerialhavingalowhysteresis loss. Itislaminatedtoreducetheeddycurrentloss.
•Theareaofthefieldpoles is increasedtoreducethefluxdensity.Asaresult, theironloss andthereactivevoltage drop are
reduced.
•Togettherequiredtorquethenumberofconductorsinthearmatureis increased.
•A compensating winding is used for reducingthe effect of the armaturereaction and improving the commutation process.

8. Thewinding is put inthe stator slot. Theaxis of compensating winding is 90degrees with the main field axis.
Thecompensating winding is connected inseries with both thearmatureand the field, hence,it is
called Conductively compensated.

9. Appliances of Universal motor

10. Advantages of Universal Motor
Universal motors have the capability to provide good
torque at low speed, which enables its use in many daily
life handheld tools operated directly through AC main
supply.
Due to the small size and less weight of the universal
motor, its use is preferred in many portable tools requiring
compact size.
Universal motors with low input power ratings ranging
from 5W to 10W are also available. These low input power
universal motors are been used in portable applications like
hairdryers, fans, electric shaver and motion projectors

11. This Photo by Unknown Author is licensed under CC BY