Charging: Principle of Operation

Simplified AC generator indicating electromagnetic induction

FIGURE. Simplified AC generator indicating electromagnetic induction.

All charging systems use the principle of electromagnetic induction to generate electrical power. Electromagnetic principle states that a voltage will be produced if motion between a conductor and a magnetic field occurs. The amount of voltage produced is affected by:

  1. The speed at which the conductor passes through the magnetic field.
  2. The strength of the magnetic field.
  3. The number of conductors passing through the magnetic field.

Alternating current is produced as the magnetic field is rotated

FIGURE. Alternating current is produced as the magnetic field is rotated.

To see how electromagnetic induction produces an AC voltage by rotating a magnetic field inside a fixed conductor (stator), refer to the illustration. When the conductor is parallel with the magnetic field, the conductor is not cut by any flux lines (A). At this point in the revolution, zero voltage and current are being produced.

As the magnetic field is rotated 90 degrees, the magnetic field is at a right angle to the conductor (B). At this point in the revolution, the maximum number of flux lines cut the conductor at the north pole. With the maximum amount of flux lines cutting the conductor, voltage is at its maximum positive value.

When the magnetic field is rotated an additional 90 degrees, the conductor returns to being parallel with the magnetic field (C). Once again, no flux lines cut the conductor and voltage drops to zero.

An additional 90-degree revolution of the magnetic field results in the magnetic field being reversed at the top conductor (D). At this point in the revolution, the maximum number of flux lines cut the conductor at the south pole. Voltage is now at maximum negative value.

Sine wave produced in one revolution of the conductor or magnetic field

FIGURE. Sine wave produced in one revolution of the conductor or magnetic field.

When the magnetic field completes one full revolution, it returns to a parallel position with the magnetic field. Voltage returns to zero. The sine wave is determined by the angle between the magnetic field and the conductor. It is based on the trigonometry sine function of angles. The sine wave shown plots the voltage generated during one revolution.

It is the function of the drive belt to turn the magnetic field. Drive belt tension should be checked periodically to assure proper charging system operation. A loose belt can inhibit charging system efficiency, and a belt that is too tight can cause early bearing failure.