DC motor is a device that convert DC electrical energy to mechanical energy and then into rotational force.
Permanent magnet dc motor
- Compactness
- Preferred – Automobiles
Separately excited motor
- These are also called servo motors.
- These require 2 DC supplies (for field & armature).
- Used as servomotor as they can be controlled from both ends.
IA = (V-Eb)/Ra
V = Eb + IaRa + Brush res drop
Ia = IL
Shunt dc motor
V = Eb + IaRa+ Brush Res. Drop
Ia = IL – Ish
Ish = V / Rsh
Eb will be governed by the current as Ish depends on the voltage, applied hence it can be controlled by varying voltages supply. For constant supply voltages flux remains approximately constant to no load to rated load operation.
Series dc motor
V = Eb + Ia (Ra + Rse) + Brush Res. Drop
Ia =IL = Ish
Long shunt dc motor
V = Eb + Ia (Ra + Rse)+ Brush Res. Drop
Ia = IL-Ish
Ish = V/ Rsh
Short shunt dc motor
V = Eb + IaRa + IL Rse + Brush Res Drop
Ia = IL – Ish
Ish = (V – IcRse )/ Rsh
