The automobile charging system provides electrical power for operation of the vehicle's ignition and starting systems and all the electrical accessories. The battery serves as an electrical storage tank, storing (in chemical form) the energy originally produced by the engine driven alternator (alternating current generator). The system also provides a means of regulating alternator output to protect the battery from being overcharged and to avoid excessive voltage to the accessories.
The storage battery is a chemical device incorporating parallel lead plates in a tank containing a sulfuric acid/water solution. Adjacent plates are slightly dissimilar, and the chemical reaction of the 2 dissimilar plates produces electrical energy when the battery is connected to a load such as the starter motor. The chemical reaction is reversible, so that when the alternator is producing a voltage (electrical pressure) greater than that produced by the battery, electricity is forced into the battery, and the battery is returned to its fully charged state.
The vehicle's alternator is driven mechanically, by a belt that is driven by the engine crankshaft. In an alternator, the field rotates while all the current produced passes only through the stator winding. The brushes bear against continuous slip rings rather than a commutator. This causes the current produced to periodically reverse the direction of its flow creating alternating current (AC ). Diodes (electrical one-way switches) block the flow of current from traveling in the wrong direction. A series of diodes is wired together in the rectifier assembly to permit the alternating flow of the stator to be converted to a pulsating direct current (DC) at the alternator output.
The alternator output is controlled by an integrated circuit (IC) voltage regulator, which is located inside of the alternator housing and is part of the alternator assembly. The voltage regulator senses the vehicle-s electrical current demand and energizes the field accordingly. It also limits the system operating range to 14.1-14.7 volts.
The battery is connected to the alternator at all times, whether the ignition key is turned on or off. If the battery were shorted to ground, the alternator would also be shorted. This would damage the alternator. To prevent this, circuit protection, in the form of either a fuse or fusible link, is installed in the wiring between the battery and the alternator. If the battery is shorted, the circuit protection will protect the alternator.