AC Generators

Note: The first charging systems used a DC generator that had two field coils that created a magnetic field. Output voltage was generated in the wire loops of the armature as it rotated inside the magnetic field. Current sent to the battery was through the commutator and the generator’s brushes.

Components of an AC generator

FIGURE. Components of an AC generator.

The DC generator was unable to produce the sufficient amount of current required when the engine was operating at low speeds. With the addition of more electrical accessories and components, the AC (alternating current) generator, or alternator, replaced the DC generator. The main components of the AC generator are:

  1. The rotor.
  2. Brushes.
  3. The stator.
  4. The rectifier bridge.
  5. The housing.
  6. Cooling fan.

Rotors

Components of a typical AC generator rotor

FIGURE. Components of a typical AC generator rotor.

The rotor creates the rotating magnetic field of the AC generator. It is the portion of the AC generator that is rotated by the drive belt.… READ THE REST

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).… READ THE REST

Charging Systems

The automotive storage battery is not capable of supplying the demands of the electrical system for an extended period of time. Every vehicle must be equipped with a means of replacing the current being drawn from the battery. A charging system is used to restore the electrical power to the battery that was used during engine starting. In addition, the charging system must be able to react quickly to high load demands required of the electrical system. It is the vehicle’s charging system that generates the current to operate all of the electrical accessories while the engine is running.

Two basic types of charging systems have been used. Hie first was a DC generator, which was discontinued in the 1960s. Since that time the AC generator has been the predominant charging device. The DC generator and the AC generator both use similar operating principles.

The purpose of the conventional charging system is to convert the mechanical energy of the engine into electrical energy to recharge the battery and run the electrical accessories.… READ THE REST