DC Motors
DC MOTOR THEORY
This increase in speed will then proportionately increase the CEMF. The speed and CEMF will
continue to increase until the armature current and torque are reduced to values just large enough
to supply the load at a new constant speed.
Summary
DC motor theory is summarized below.
DC Motor Theory Summary
There are two conditions necessary to produce a force on a conductor:
-
The conductor must be carrying current.
-
The conductor must be within a magnetic field.
The right-hand rule for motors states that when the forefinger is pointed in the
direction of the magnetic field lines, and the center finger is pointed in the
direction of current flow, the thumb will point in the direction of motion.
The function of torque in a DC motor is to provide the mechanical output to
drive the piece of equipment that the DC motor is attached to.
Torque is developed in a DC motor by the armature (current-carrying conductor)
being present in the motor field (magnetic field).
CEMF is developed in a DC motor by the armature (conductor) rotating (relative
motion) in the field of the motor (magnetic field).
The function of the voltage that is developed in a DC motor (CEMF) opposes the
applied voltage and results in the lowering of armature current.
The speed of a DC motor may be changed by using resistors to vary the field
current and, therefore, the field strength.
Rev. 0
Page 7
ES-06
