Charging System Fundamentals

Learning Objectives:

• You will be able to explain the basic parts of a charging system

• Explain the charging system operation using the correct terminology

• Demonstrate basic troubleshooting on a charging system

• You will be able to explain charging system indicators

Charging System Function

• It recharges the battery after engine cranking or after the use of electrical accessories with the engine shut off.

• It supplies the entire car’s electricity when the engine is running.

• It provides a voltage output that is slightly higher than battery voltage.

• It changes output to meet different electrical loads.

Types of charging systems• There are two basic charging systems: Alternator (A/C

generator) system and (D/C generator) systems. Alternator charging (A/C) systems have replaced the older direct current (D/C) systems.

• The D/C Generator

was fine for producing electricity on early model vehicles. However, today’s vehicles have more electrical components requiring high-current output.

• A D/C generator would not be able to supply enough current for a modern vehicle at idle speed. The efficiency of a generator is poor at low engine speeds.

DC Generator

A/C Generator

• It is smaller, lighter, and more dependable than a DC generator. The alternator will also produce more output at idle than a DC generator.

• The alternator has a spinning magnetic field.

Alternator operation • The two main parts of a simplified alternator are the rotor

and stator. • alternator rotor is located in the centre of the alternator

housing. Two claw shaped pole pieces surround the field windings to increase magnetic field strength. It creates a rotating magnetic field. The alternator drive belt turns the rotor, making the field rotate.

Alternator Brushes

• Alternator brushes ride on the slip rings to make a sliding electrical contact. The brushes feed battery current into the slip rings and rotor windings, creating an electro-magnet.

Alternator Stator• The stator consist of three groups of windings. The coils

are wrapped around a soft laminated iron core. • The stator produces the electrical output of the alternator.

The stator windings connect to the diode assembly.

Alternator Rectifier

• A diode assemble commonly uses 6 diodes to convert stator output which is alternating current (AC) into direct current (DC). The rectifier diodes are mounted in a diode heat sink.

Alternator Fan

• To provide cooling for the alternator, an alternator fan is mounted on the front of the rotor shaft.

• This cools the windings and diodes to prevent overheating and damage. Normally the fan is located between the pulley and the front bearing.

Voltage Regulator• A voltage regulator controls alternator output by changing the

amount of current flowing through the rotor windings. • Any change in rotor winding current changes the field strength

acting on the stator.• The voltage regulator can maintain a preset charging voltage around

13.0 – 13.9 volts.

Voltage Regulator Styles

Internal Regulator External Regulator

Alternator Warning Light• An alternator warning light is wired into the charging system

so that it will glow when alternator output drops to a specified level.

• If a problem develops in the charging system, or the field current is trying to increase the alternator output, this will cause the indicator bulb to glow.

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