Automotive Alternator Components and Operation
Automotive Alternator Components
Overview
The automotive alternator consists of the following components:
- Rotor (inductor)
- Stator (armature)
- Bridge rectifier diodes
- Covers, fan, and other complementary elements
Rotor or Inductor
The rotor, the moving part of the alternator, generates the magnetic field that induces current in the stator windings. It consists of a shaft with a magnetic core made of forged steel. The core has interlaced protrusions (poles) that create a magnetic field. An insulated copper wire coil is wound around the core. Slip rings and carbon brushes transmit the excitation current to the coil.
Stator or Armature
The stator is the stationary part of the alternator where the current is generated. It has a frame made of laminated electrical steel with slots to house the windings. Three separate windings are distributed in the slots, forming the three phases of the alternator. These windings can be connected in a star or delta configuration to produce three-phase alternating current.
Bridge Rectifier Diodes
The alternating current generated by the alternator needs to be rectified to direct current for the battery and vehicle’s electrical system. A bridge rectifier, typically consisting of 6 or 9 silicon diodes, converts the AC to DC. The diodes are mounted on a heat sink to dissipate the heat generated during operation.
Housing, Fan, and Cooling
The alternator components are housed within aluminum casings. A fan, driven by the rotor shaft, circulates air through the alternator to dissipate heat. Different fan configurations, such as single-flow and dual-flow, are used depending on the alternator’s design and cooling requirements.
Alternator Excitation Circuit
The alternator requires an excitation current to generate electricity. Initially, before the engine starts, the excitation current is supplied by the battery through a pre-excitation circuit. Once the engine is running, the alternator becomes self-excited and generates its own excitation current through a field circuit.
Pre-excitation Circuit
The pre-excitation circuit consists of the battery, ignition switch, and a control lamp. This circuit provides the initial excitation current until the alternator reaches a sufficient voltage to sustain itself.
Self-excitation Circuit
Once the alternator is generating enough voltage, the control lamp turns off, and the alternator switches to self-excitation. It uses a portion of its own output voltage to power the field circuit, maintaining the magnetic field and generating electricity.