Charging System Guide

The car charging system comprises a generator, battery, voltage regulator, charging indicator, related wires, and other supporting parts. These components work together to power electrical equipment and keep the battery charged while the engine is running.

Many people think the battery is the main power supply of the car, but in normal driving, the generator is the real power source. The battery mainly supports starting and assists when generator output is not enough.

System structure

Main components

What the Car Charging System Includes

  • Generator.The generator is the main power source for the car’s electrical equipment. During normal operation, it supplies power to electrical equipment except the starter and charges the battery.
  • Battery.The battery is the largest electrical equipment on the car. Its main role is to power the starter, ignition system, and other major electrical equipment during engine start, and to supply equipment when the engine is not running or is running at low speed.
  • Voltage regulator.The voltage regulator adjusts the generator output voltage so that the generator output voltage is maintained between 13.8-14.4 volts.
  • Charging indicator system.The charging indicator system mainly refers to the voltmeter or charging indicator on the dashboard. It indicates whether the generator working status is normal.
Generator and battery

Power supply roles

Generator and Battery Responsibilities

When the engine is running normally, almost all electricity on the car is provided by the generator. When there is power left, the generator charges the battery. The power of a general car generator is about 0.8-1.5 kW, which can meet the car’s electricity demand in most cases, and the battery supplements it when power generation is insufficient.

In some small-displacement engines, when the generator generates more power and creates a higher load, the engine may shake due to the increased load. The engine will automatically increase speed to enhance engine power.

Most automobile generators are silicon rectifier three-phase alternators, using silicon diodes as rectifiers to convert alternating current into direct current. The main structure includes the rotor, stator, brush and slip ring mechanism, three-phase bridge rectifier, bearings, fan, and front and rear end caps. The rotor generates a magnetic field, the stator sends current, and the rectifier converts three-phase AC into DC pulsating voltage. Generator power generation increases with engine speed.

The battery also stabilizes the voltage of the power supply system. It is equivalent to a large capacitor, absorbing instantaneous overvoltage in the circuit to protect electrical equipment. When the engine works normally, the generator output voltage is higher than the voltage of the car battery, so the generator supplies all electrical equipment except the starter and charges the battery. The battery uses its internal stored energy to drive the starter mainly when the engine starts.

Working principle

Excitation and rectification

How the Car Charging System Works

When we turn on the ignition switch, the battery provides excitation current to the rotor of the generator, and the rotor produces a magnetic field. Then the engine starts and drives the generator to run. The stator winding cuts the magnetic lines of the rotor winding, producing three-phase AC current, which is turned into DC power after silicon rectification and output to the outside.

At this time, because the generator speed is low, its excitation current is provided by the battery. As the generator speed becomes higher and higher, the power generation becomes larger and larger, and the rotor winding current is provided by the generator’s own current. This is called “self-excitation.”

When the engine works normally, the generator also runs at high speed with the engine, sending electrical energy to the car’s electrical equipment, and excess power is used to charge the battery. When the battery is full, the voltage regulator disconnects the excitation current of the rotor and the generator stops generating electricity. When the battery voltage decreases to a certain value, the voltage regulator reconnects the excitation current and the generator resumes generating electricity.

This process repeats to ensure the normal operation of the car’s electrical equipment and keep the battery fully charged. To ensure that the car can generate electricity even at low speed, the general generator speed is 2.5-3 times the engine speed, so even when the engine is idle, the generator can generate electricity normally.

Faults and maintenance

Charging indicator and daily inspection

Common Charging System Failures and Checks

If the charging indicator lights up, or the voltmeter pointer is lower than 24V when the car is running, it means that the generator is not charging or the charging amount is too low, and the charging system needs to be overhauled.

Common failures of car charging systems include not charging, overcharging, and undercharging. The causes of the failures are mainly poor line contact and generator failure. Generally speaking, modern generators are highly integrated and cannot be disassembled and repaired under normal conditions; they can only be replaced as a whole.

During use, do not use the generator output instantaneous grounding method to determine whether the generator generates electricity, and do not remove the battery or other major electrical equipment when the generator is running at high speed. Otherwise, surge voltage may break down precision electronic components.

In daily maintenance, often check the connection between the generator and the battery to ensure that the connection is solid and reliable, with no rust at the joints. Also check the tension of the generator belt. If the belt is too loose, the generator speed may be too low for power generation. If the belt is too tight, it can easily damage the belt and generator bearings.

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