Notes on Starting Motor and Electromagnetism

Overview of Starting Motors

• Historical Context:
  • Early cars started with a hand crank, which was dangerous.
  • Modern vehicles use an electric starting motor for this process.

Functionality of the Starting Motor

• Starting Motor Mechanics:
  • Pressing the starter switch connects the starting motor to the flywheel.
  • Electric current from the battery activates the starting motor.
  • The Armature rotates due to the electric current, performing the mechanical work needed to crank the engine.
  • Gearing is involved with a pinion gear connecting the Armature to the flywheel.

Principles of Electromagnetism

• Electricity and Magnetism Connection:

  • Flowing current produces a magnetic field around a conductor.
  • The strength of the magnetic field increases with the strength of the current.
  • Movement is key: either the conductor moves through a magnetic field, or the magnetic field moves across the conductor.

• Characteristics of Magnets:

  • Every magnet has a North and South Pole.
  • Unlike poles attract; like poles repel.
  • Repulsion occurs when same poles (N-N or S-S) are near each other.

Electromagnetic Action

• Formation of Electromagnets:

  • A current-carrying loop of wire acts as an electromagnet with its own North and South poles.
  • Direction of current determines North/South orientation of the loop.
  • When the loop is positioned near a bar magnet, it experiences repulsion and attraction, causing rotation.

• Rotation Mechanism:

  • The loop rotates to align with the magnet's opposite pole but momentum carries it past alignment.
  • Current direction change happens just before alignment, allowing continuous rotation.
  • Segments and brushes facilitate this current direction change to maintain rotation.

Components of the Motor

• Segments and Brushes:

  • Segments are copper, conduct electricity, and rotate with the wire loop.
  • Brushes remain stationary connections to the power source (battery).

• Armature Construction:

  • Multiple loops/windings around an iron core are necessary for sufficient power.
  • Each winding has its own segments, working together to maximize rotational effort.

Application of Power

• Magnetic Field Enhancement:
  • Larger magnets are unwieldy; starting motors use pole pieces with conductors wound around them to enhance the magnetic field.
  • This greatly strengthens the Armature's turning power.

Summary of Motor Operation

• Circuit Operation:
  • Closing the starter switch completes the battery-motor circuit.
  • Current flow gives polarity to Armature and field coils, causing rotation.
  • The Armature's rotary power is transmitted to the flywheel, cranking the engine.

Conclusion

• Efficiency of Starting Motors:
  • Automotive starting motors are designed to produce substantial power relative to their size.