DC Motors and Generators

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Forging new generations of engineers
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DC Motors and Generators

• Instruction Plan

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Motor Basics

• A. How motors use magnetic force
• 1. Constant opposing and attracting of magnetic
• forces are needed for a motor to run.
• 2. Armature is on a rotating shaft
• a. Direction of current flow determines the
  magnetic poles of the armature
• b. Changes in the direction of current flow can
  occur while the armature rotates
• 3. Commutator reverses direction of current flow
• B. Timing in a motor is controlled by the angle
  of
• commutation.

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The Permanent Magnet Motor

• A. Specific dc motors are used for different
  purposes.
• B. Two permanent magnets which are apart create a
  magnetic field between them.
• 1. Magnetic poles of the magnets do not change
• 2. Magnetic poles of the armature can change
• 3. Motor can change direction if the voltage to
  the armature changes
• C. DC motors can operate in a clockwise or
  counter-clockwise direction.
• D. The strength of the magnetic field affects the
  speed and operation of the motor.

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The Series DC Motor

• A. Motors which operate large loads require
  stronger magnetic fields.
• 1. Electromagnets are used instead of permanent
  magnets.
• 2. The field coil is wired in series with the
  armature windings.
• B. Counter emf is the voltage produced in the
  armature when it cuts through the magnetic field
• 1. Cemf opposes the power supply voltage.
• 2. Cemf determines amount of current flow,
  torque and speed.
• 3. As motor speed increases, cemf increases

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Compound Motors

• A. Combination of series and shunt motors
• 1. Torque abilities of series motor
• 2. Constant speed advantages of a Shunt motor
• B. Uses both a series and shunt field coil
• C. Cumulative compound motor has series and shunt
  coil connected to aid one another
• D. When the speed is increased, the torque
  decreases
• E. Current through the shunt field coil remains
  the same, limiting the speed of the motor
• F. Compound motors are not used as extensively as
  series or shunt motors

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Generator Action

• A. Generators supply electrical energy to motors
• Convert mechanical energy to electrical energy
• Voltage is induced by passing a wire through a
• magnetic field
• a. When the wire is moved up and down, the
  induced voltage reverses direction
• b. Amount of voltage determined by speed of the
  wire moving through the magnetic field
• B. Generators use coils of wire to produce
  electrical energy
• Armatures are coil that rotate in a magnetic
  field
• The faster the armature rotates, the greater the
• amount of voltage produced