GM Cavalier/Sunbird/Skyhawk/Firenza 1982-1994

Description and Operation

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See Figures 1, 2, 3 and 4



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Fig. Fig. 1: Sectional view of the SI model alternator



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Fig. Fig. 2: Sectional view of the CS model alternator

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 surge of storage tank, storing (in chemical form) the energy originally produced by the engine driven generator. The system also provides a means of regulating generator 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 two 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 generator is producing a voltage (electrical pressure) greater then that produced by the battery, electricity is forced into the battery, and the battery is returned to its fully charged state.



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Fig. Fig. 3: Schematic of the SI model alternator



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Fig. Fig. 4: Schematic of the CS model alternator

The vehicle's generator is driven mechanically, through V belts, by the engine crankshaft. It consists of two coils of fine wire, one stationary (the stator), and one movable (the rotor). The rotor may also be known as the armature and consists of fine wire wrapped around an iron core which is mounted on a shaft. The electricity which flows through the two coils of wire (provided initially by the battery in some cases) creates an intense magnetic field around both rotor and stator, and the interaction between the two fields creates voltage, allowing the generator to power the accessories and charge the battery.

Todays automobiles use alternating current generators or alternators because they are more efficient, can be rotated at higher speeds, and have fewer brush problems, In an alternator, the field rotates while all the current produced passes only through the stator windings. The brushes bear against continuous slip rings rather than a commutator. This causes the current produced to periodically reverse the direction of its flow. Diodes (electrical one-way switches) block the flow of current from traveling in the wrong direction. A series of diodes is wired together to permit the alternating flow of the stator to be converted to a pulsating, but unidirectional flow of current from traveling in the wrong direction. A series of diodes is wires together to permit the alternating flow of the stator to be converted to a pulsating, but unidirectional flow at the alternator output. The alternator's field is wires in series with the voltage regulator.

The alternating current generator (alternator) supplies a continuous output of electrical energy at all engine speeds. The alternator generates electrical energy for the engine and all electrical components, and recharges the battery by supplying it with current. This unit consists of four main assemblies: two end frame assemblies, a rotor assembly, and a stator assembly. The rotor is supported in the drive end frame by a ball bearing and at the other end by a roller bearing. These bearings are lubricated during manufacture and require no maintenance. There are six diodes in the end frame assembly. Diodes are electrical check valves that change the alternating current supplied from the stator windings to a direct current (DC), delivered to the output (BAT) terminal. Three diodes are negative and are mounted flush with the end frame; the other three are positive and are mounted into a strip called a heat sink. The positive diodes are easily identified as the ones within small cavities or depressions. A capacitor, or condenser, mounted on the end frame protects the rectifier bridge and diode trio from high voltages, and suppresses radio noise. This capacitor requires no maintenance.

 
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