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Introduction

To know why testing of a DC motor is required, we have to understand its operation working principle, and losses first. Then we can discuss How to test dc motor in an easier way.

basic principles of dc motors

Basic principles of DC motors

A DC motor converts DC electrical energy into mechanical energy and works on the principle of electromagnetic 🧲 induction I.e we can say that it converts DC Input power into mechanical output power. During this due to back emf whole input power can not be converted as output machinical power.

DC motor includes  two types of windings 

The first is field winding and the other is armature winding. We can find the direction of motion by using Flemming's left-hand rule, in which the index and middle fingers of the left hand are in the direction of the magnetic field and current, then the thumb indicates the direction of motion i.e. force.

Back emf

Just start with the basic DC motor During its operation it has a magnetic field it may be through an electromagnet or a permanent magnet. As we know in a DC motor. We give a supply to the armature which has a coil After giving the supply it acts like an electromagnet and in that magnetic field the armature is placed which also has a coil in it due to which when the armature starts its rotation in a magnetic field, there is a generated induced emf in its coil this emf is known as back emf, which weakens the main field flux and overall the efficiency of a DC motor.

Classification of DC motors

DC motors are classified into 3 types 

A. DC series motor

B . DC shunt motor.

C. DC compound motor.

DC series motor:

In this type of motor field windings are thick and hence resistance is low starting torque is very high, and its motion depends on the load.

Uses of DC series motor - 

-In traction work

-in self-starter in motor vehicles 

-cranes 

-lift 

DC shunt motor - 

The field winding is made of thin wire and hence its resistance is high. On starting in zero load the torque of this motor is very low 

Uses of DC shunt motors-

-leth machines 

-machine tools, etc.

DC compound motors- 

Its winding is the mixture of series and shunt-type DC motors and hence it is used in Rolling mills, and printing presses.

Efficiency of a DC motor

It is described as output power/input power After learning the basic principles of DC motor, types, and losses  After having any problem with the DC motor or calculating losses in the DC motor we have various types of testing used to test the DC motor -

Various types of testing in DC motor -

1. Direct test or Brake test of DC motor

2. Indirect test Swinburne test or Hopkins test of DC motor.

How to test DC motor by Direct or Brake testing

This test is performed to calculate the loss and efficiency of a DC motor. This test is performed on full load. This test applies to the DC series motor.

Brake test - performed on a less powerful motor
Field test - performed on the high-power motor.

How to test DC motor by Indirect testing or Swinburne testing

This test was performed on no load. This test was applied to the shunt motor. During no load test, current directly goes into the winding of the motor due to which the temperature of the winding increases. Due to this, it is suitable for shunt motors in which windings are parallel to the armature. Due to the commutation effect and increase in temperature, this test doesn't not satisfactory results. Power loss is less in this testing.

How to test DC motor by Hopkin's test or back-to-back testing

This is also known as the regenerative test. Two identical types of shunt machines are connected to the test. This is a full load test. The commutation properties of the shunt motor can be calculated by this test. temperature increase is also calculated by this test. This test is performed on large-sized motors. The drawbacks of the Swinburne test can be overcome by using this test.

Safety precautions for DC motor

  • The commutator should be cleaned regularly.
  • if there are small patches developed in the commutator segment it should be filled by wax, due to which carbon can not be settled in those patches.
  • The pressure of brushes should not be more or less on the commutator segment due to which sparking occurs.
  • if there is no interpole then the brush rocker should be placed on a neutral point.
  • The commutator should be round in shape and there should not be any holes in it.
  • the motor should not be operated on overload conditions.
  • the motor should start at a low speed.
  • the motor should not be started without using a starter.

Problem preventive maintenance of a DC motor -

  • connection wires should be checked regularly.
  • the air gap between the armature and the stator should be checked.
  • The bearings of the motor should be checked.
  • The heat developed in the motor should be checked.
  • small problem should be checked.

Routine maintenance of DC motor -

  • Nearby areas should be cleaned.
  • The power supply should be checked 
  • During operation, if the motor produces any sound then the main switch immediately be turned off.
  • The nuts and bolts of the motor should be checked regularly.

Conclusion - how to test DC motor and basic principles of dc motors

So in this short blog, we learned the basic principles of dc motors, back emf, classification, and losses, and we learned How to test DC motor and various types of testing in DC motors.

Hope this helps you.

Thank you for reading.

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