Types of dc motor

DC motor is a device that convert DC electrical energy to mechanical energy and then into rotational force.

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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