A brief introduction to DC motors

1. A brief introduction.
DC motors
By
Srinivas R Bhat

2. What is a MOTOR?
 A device which converts electrical energy into
mechanical energy.
 DC – Direct current.
 Some other types of motors are.
 Induction motor.
 Synchronous motor.
 BLDC motor.
 Stepper motor.
 Switched reluctance motor.

3. Mechanical Construction.
 Any motor consists of a stationary part – Stator
and a rotatory part- Rotor.
 Generally in a DC motor Stator houses the Field
coils which produces magnetic field. Also a
permanent magnet can be found in some motors
instead of field coil.
 The rotor in DC motors is also called as
Armature.
 Armature consists of commutator segments and
brushes provide electrical contact to armature.
 Brushes- Carbon(Graphite).

4. Stator
Armature

5. Armatures

6. Working principle
 Force is experienced by a conductor carrying
current in a magnetic field.

7.  When the motor starts to rotate back-emf is
generated in the coil.
 To do the work current is to be pumped against
the back emf.
 Power balance equation
Torque×Speed = Back emf×Current.
 Torque is proportional to input currrent under
constant speed.
 Speed majorly depends on Field current (flux).

8. Types of DC motors
- based on type of field and armature connection.
 Shunt motor.
 Series motor.
 Compound motor.
 Short shunt .
 Long shunt.
 The characteristics of motor also vary according
to connection.
 Seperately excited motors.

11. Note on Reversal of motor
direction.
 To reverse the rotation of the motor either field
current is to be reversed or polarity of excitation
applied to motor armature should be reversed.
 Normally in small motors reversing the terminals
of the motors does the job as there is permanent
magnetic field.
 It is achieved by a H-bridge arrangement of
contactors.
 Sophisticated Drive systems are available for
higher capacity motors for different operation.

12. Speed torque characteristics

13. Applications
 DC motors provide excellent torque range at
constant speeds and hence were extensively use
for Traction System.
 They also provide efficient speed control over a
good range at constant torque.
 But now due to advancement in drive technology
like VFDs and power electronics based drives DC
motors are being substituted by Induction motors.
 But they are making their presence felt still in the
form of BLDC motors where in the commutation is
done by electronics means instead of brushes.

16. THANK YOU