DC Motor Maintenance (A8014)

Learn the procedures for disassembling, inspecting, cleaning, and reassembling DC motors and their components.


This lesson is designed for participants familiar with basic electrical principles, electrical safety, electrical print reading, electrical control equipment, Ohm’s Law and Three-Phase Motors.


This lesson introduces participants to the application of direct current motors and their components. This lesson covers general characteristics of a DC motor, DC motor components, their functions and the design of the brush assembly. This lesson explains concepts such as flux interaction, commutation, the effect of multiple windings, armature’ reaction, compensation and CEMF, and how each of these factors effects motor operation.


Know the general requirements of a DC motor and what requirements they meet. Be able to identify the basic components and explain the functions of a DC motor. Identify the components of the brush assembly and explain its function. Explain the effect of armature current on the main flux field and how this results in motor action. Explain the process of commutation and how this maintains direct current in a DC motor. Describe how the number of windings and commutator segments effects torque and mechanical power. Explain how armature reaction shifts the neutral plane, how it affects motor operation, and what measures will correct the reaction. Know the requirements for induced voltage in a motor, and explain Counter EMF.  Explain the designs of a series wound, shunt wound, compound wound, and permanent magnet wound motor and how each of them work. Learn about reduced voltage starters and what determines the direction of the rotation of a motor. Learn how a reverse contractor works.  Know how a tapped resistor and field rheostat work. Know how a drive control system works.