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Automotive
Charging Systems

After the battery has supplied the high current needed to start the engine, even a good battery has a low charge. The charging system recharges the battery by supplying a constant and relatively low charge to the battery.

The Alternator

Charging systems work on the principle of magnetism to change mechanical energy into electrical energy.

Voltage is induced in a wire when it moves through a magnetic field. The wire or conductor becomes a source of electricity and has a polarity or distinct positive and negative ends.

This polarity can be switched depending on the relative direction of movement between the wire and the magnetic field. This is why an AC generator produces alternating current.

Once the engine is running, the charging system is responsible for producing enough energy to meet the demands of all of the loads in the electrical system, while also recharging the battery.

With all of the electrical and electronic devices found on today's cars, the charging system has a difficult job.

In an alternator (sometimes referred to as an AC generator) a spinning magnetic field (called the rotor) rotates inside an assembly of stationary conductors (called the stator).

As the spinning north and south poles of the magnetic field (rotor) pass the conductors (stator), they induce a voltage that flows first in one direction and then in the opposite direction (AC voltage).

Because automobiles use DC voltage, the AC voltage created must be converted or rectified into DC Voltage.
- This is done through an arrangement of diodes that are place between the output of the winding's and to output of the AC Generator. A diode is an electronic device that allows electricity to pass through it in only on direction. A number of diodes are used in the alternator to change the AC electrical current (Alternating Current) to DC current (Direct Current).
- When AC passes through a diode, only the negative pulses are blocked off. This would cause pulsating current flow. By adding more diodes to the circuit, more of the AC is rectified. This allows for a full flow of electrical current.

Voltage output of an AC generator can reach as high as 250 volts if it is not controlled. The battery and the rest of the electrical system must be protected from this high voltage.
- A voltage regulator is used to control the voltage output of an AC alternator.
- Regulation of voltage is accomplished by varying the amount of field current flowing through rotor. The higher the field current, the higher the voltage output.
- To ensure that the battery stays fully charged, most regulators are set for a system voltage between 14.5 and 15.5 volts.

The alternator is driven by a belt from the engine crankshaft pulley. From the time a car is first started, until the alternator is rotating fast enough to begin charging, the battery supplies all the electrical power for all the needs of the vehicle.

Belt Routing