Automotive Dynamo and Alternator: Function & Components

Purpose and Function of an Automotive Dynamo

The dynamo's mission is to transform mechanical energy received at its axis into electrical energy collected at its terminals. It acts as a power supply circuit for vehicle loads, using this power to charge the battery, where it is stored for later use to provide services in automotive applications and, in turn, feeding various circuits and accessories installed in the vehicle.

Components of a Dynamo

• Stator (Inducer Group)

  This group consists of the casing, the pole pieces (or polar bodies), and coils. Its aim is to create the stator magnetic field within which the induced coil moves. The casing is made of steel, through which the magnetic circuit closes. The pole pieces are inside the casing and attached to it by screws driven from the outside. The induction coil is formed by several turns of copper wire. They are responsible for creating the inductor magnetic field, which, as it passes through them, creates dynamic flux.

• Rotor (Induced Group)

  Its purpose is to generate the usable current. This consists of a steel shaft and a cylinder formed by a set of magnetic plates, which together form the slots where the induced conductors are housed. These conductors are attached to copper foils that form the commutator segments. The commutator's mission is to transform the continuously alternating voltage and current into direct current.

• Brush Holder and Lid

  It consists of supports, one of which is insulated, on which the brushes slide. These brushes are driven by spiral springs, which provide sufficient pressure to maintain contact with the commutator. The brushes are in contact with the commutator and are responsible for collecting the current generated by the dynamo. One brush is mounted to ground (mass) and the other to the isolated positive (+) terminal/outlet. They are manufactured from carbon with 10% to 15% graphite, a material that provides a soft contact.

Alternator Inspection and Operation

Before performing various checks, you should clean the alternator, removing grease, dust, mud, etc.

1. Rotor Inspection

   Inspect for the absence of cracks, deformation, signs of oxidation, or ensure the smooth appearance of slip rings.

2. Voltage and Current Generation in Alternators

   The production of electricity in the alternator is very similar to that in a dynamo. In the dynamo, there is a static magnetic field in the stator. As the rotor spins, its coils cut through the magnetic field in the stator, generating voltage within them. The key difference from the dynamo is that the magnetic field itself is moving. As this field moves, it is cut by the stator's coils, creating voltage and current.

3. Alternator vs. Dynamo: Key Differences

   The alternator does not use a commutator (thin collector). Current rectification in the alternator is achieved through a rectifier assembly. The brushes are only used to feed the induction coil, and since the exciting current is small, their wear is significantly less due to the continuous surfaces of the slip rings. In the absence of a commutator, the rotor can turn at higher revolutions.