Function of Automotive charging system


Vehicle is equipped with many electrical devices to drive safely and comfortably. The vehicle requires electricity not only while driving but also while it stops.
Therefore, the vehicle has a battery for a power supply and a charging system to generate electricity by the engine running. The charging system supplies electricity to all the electrical devices and charges the battery.

Construction of charging system and flow of electricity

Charging system mainly consists of the following devices.

Alternator – While the engine is running, this generates a nearly equal amount of electricity to operate the electric devices used for the vehicle and to charge the battery.

Regulator (built in the alternator) -This is a device to regulate the generated voltage in order to make it constant even when the alternator speed changes or current volume that flows into the electric devices fluctuates.

Battery – This is a power source when the engine stops and it supplies electricity to the electric devices to start the engine or when the alternator does not generate electricity. However, electricity generated by the alternator is charged to the battery once the engine starts running.

Charge warning light – This informs of the malfunction in the charging system.

Ignition switch

Flow of electricity in charging system
Electricity in each position of the ignition switch.

Ignition switch ACC or LOCK

Ignition switch ON (when 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 engine is running)

3. The function of alternator

The alternator plays a major role in the charging system. 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 electromagnetized 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.

1. Three-phase alternating current

(1) When a magnet rotates within a coil, a voltage will be created between both ends of the coil. This will give rise to an alternating current.

(2) The relation between the current generated in the coil and the position of the magnet is as shown in the figure. The largest amount of current is generated when the N and S poles of the magnet are closest to the coil. However, the current flows in opposite direction with each half turn of the magnet. Current that forms a sine wave in this manner is called “single phase alternating current”. A change of 360

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