CHARGING SYSTEM: COMPONENTS, FUNCTIONS, WORKING PRINCIPLE AND DIAGNOSIS TIPS

WORKING PRINCIPLE

The flow of electricity in the charging system

Electricity in each position of the ignition switch.

Ignition switch ACC or LOCK

Ignition switch ON (when the engine is not running)

When the ignition switch is in the ON position, current flows from the battery to the alternator. The reason for this is as follows. The alternator generally used for the vehicle generates electricity by rotating the magnet. The magnet is not the permanent magnet but the electromagnet that generates magnetic force by flowing electricity inside. Therefore, it is necessary to supply electricity to the alternator before starting the engine to prepare for generating electricity.

Ignition switch ON (when the engine is running)

FUNCTIONS OF ALTERNATOR

The alternator plays a major role in the charging system. The alternator has three functions of generating electricity, rectifying current and regulating voltage.

(1) Generation

Transmitting the engine revolution to the pulley via the v-ribbed belt turns the electromagnetic rotor, generating alternating current in the stator coil.

(2) Rectification

Since the electricity generated in the stator coil is alternating current, this cannot be used for the DC electric devices installed on the vehicle. To use the alternating current, the rectifier is used to rectify the alternating current into direct current.

(3) Regulation of voltage

IC regulator regulates the generated voltage to make the voltage constant even when the alternator speed or the amount of current flowing into the electric devices change.

CHARGING SYSTEM DIAGNOSIS

The following general information has been assembled as a guide for charging system diagnosis. Refer to the appropriate Original Equipment Manufacturer’s service manual for specific information pertaining to charging system diagnostic procedures and safety precautions for your vehicle.

BENCH TESTING

If an alternator test bench is available, follow the procedures found in the bench tester’s instruction manual to conduct an alternator performance test.

This test will determine if the alternator output is within its performance specification, preventing unnecessary alternator replacement.
If the alternator output is within specification during bench testing, resolve problems in the remainder of the vehicle’s charging circuit and other electrical circuits that may affect charging circuit performance.

Refer to the appropriate vehicle manufacturer’s service manual for the procedures and circuit schematics necessary to identify and correct additional charging circuit problems.
If the test bench results show the alternator’s output performance to be out of specification, replace the alternator.

Follow the vehicle manufacturer’s recommended procedures to inspect the remainder of the charging circuit and other electrical circuits that may affect charging circuit performance.

NOTE: If the bench test identifies the regulator as defective, it may be possible to replace the regulator (internal or external) and return the alternator to service.

If the regulator is replaced and the alternator returned to service, follow the vehicle manufacturer’s recommended procedures to inspect the remainder of the charging system and other electrical circuits that may affect charging circuit performance.

Whether or not a test bench was used to determine the condition of the alternator, the following Helpful Tips have been assembled to help isolate conditions that may affect charging circuit performance.