MAGMO

PERMANENT MAGNET DC MOTOR

CONTENTS

Introduction

Working principal of DC motor

Construction of PMDC motor

Rotor or armature of PMDC motor

Working

A current carrying conductor is placed inside a magnetic field, there will be mechanical force experienced by that conductor

When permanent magnet is used to create magnetic field in a DC motor, the motor is referred as permanent magnet DC motor or PMDC motor

INTRODUCTION A DC motor in simple words is a device that

converts direct current(electrical energy) into mechanical energy.

PMDC are best solutions to motion control and power transmission applications where compact size, wide operating speed range, ability to adapt to a range of power sources or the safety considerations of low voltage are important

Motivation to choose this topic

Conveyors Electric Chairs

Door openers

Magnets are mounted in periphery of this cylinder.

The stator also serves as low reluctance return path for magnetic field.

Sometimes field coil is used in PMDC motor because if permanent magnet lose their strength, these lost strengths can be compensated by field excitation through these field coils

STATOR

made of number of varnish insulated, slotted circular lamination of steel sheets

Varnish insulated are used to reduce eddy current loss

ROTOR(ARMATURE)

Similar to DC motor

Consists of core, windings, and commutator

A stator and an armature

N – pole and S – pole of each magnet are alternatively faced towards armature

Cylindrical stator serves as low reluctance return path for the magnetic flux

Permanent magnets lose their strength, these lost magnetic strengths can be compensated by field excitation through these field coils

CONSTRUCTION

Working principal of PMDC motor

A DC motor in simple words is a device that converts direct

current(electrical energy) into mechanical energy.

FLEMING’S LEFT HAND RULE

Fleming’s left hand rule says that if we extend the index finger, middle finger and thumb of our left hand in such a way that the current carrying conductor is placed in a magnetic field (represented by the index finger) is perpendicular to the direction of current (represented by the middle finger), then the conductor experiences a force in the direction (represented by the thumb) mutually perpendicular to both the direction of field and the current in the conductor.

The working principal of PMDC motor is same as the working principal of DC motor

Direction of this force is governed by Fleming’s left hand rule

each conductor of the armature experiences the mechanical force F=BIL

When a carrying conductor comes inside a magnetic field, a mechanical force will be experienced by the conductor

Each conductor of the armature experiences a force and the compilation of those forces produces a torque, which tends to rotate the armature.

WORKING

For smaller ratings, use of permanent magnets reduces manufacturing cost.

No need of field excitation winding, hence construction is simpler.

No need of electrical supply for field excitation, hence PMDC motor is relatively more efficient.

Relatively smaller in size

Cheap in cost

The permanent magnets supply the surrounding field flux, eliminating the need for external field current. This design yields a smaller, lighter, and energy efficient motor.

Advantages

Since the stator in PMDC motor consists of permanent magnets, it is not possible to add extra ampere-turns to reduce armature reaction. Thus armature reaction is more in PMDC motors.

Stator side field control, for controlling speed of the motor, is not possible in permanent magnet dc motors.

Disadvantages

APPLICATIONS

TOYS Drilling Machine

Electric Toothbrush

Automatic Door opener

Gear motor Coveyors

REFERENCE

http://www.electrical4u.com

http://www.completepowerelectronics.com/

www.learnengineering.org

THANK YOU