Chrysler Full-Size Trucks 1989-1996 Repair Guide



See Figures 1, 2 and 3

The automobile charging system provides electrical power for operation of the vehicle's ignition and starting systems as well as for all the electrical accessories. The battery serves as an electrical surge or storage tank, storing (in chemical form) the energy originally produced by the engine driven generator. The charging system also provides a means of regulating generator output to protect the battery from being overcharged and to avoid excessive voltage to the accessories.

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Fig. Fig. 1: Components of a common charging system-note the diagnostic tool hookup

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 when the generator is producing a voltage (electrical pressure) greater than that produced by the battery, electricity is forced into the battery, returning it to a fully charged state.

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Fig. Fig. 2: Common alternator mounting-gasoline engines

The alternator is driven mechanically, through belts, or a serpentine belt, via 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 most cases) creates an intense magnetic field around both the rotor and stator; the interaction between the two fields creates voltage, allowing the generator to power the accessories and charge the battery.

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Fig. Fig. 3: Common alternator mounting-diesel engine

The vehicles covered by this guide use Alternating Current (AC) 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 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. 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 at the alternator output. The alternator's field is wired in series with the voltage regulator.

The voltage regulator controls the level of voltage produced (and sent to the battery). On gasoline-powered models, the regulator's field control circuitry is contained in the engine controller computer. This circuitry is connected in series with the second rotor field terminal and ground. To regulate the voltage output, the ground path is cycled on and off. The degree to which it is on or off is determined by the findings of the voltage regulator circuitry which monitors system line voltage and ambient temperature. On diesel models, the voltage regulator is an external electronic unit that is wired into the current supply to the alternator.

The alternator is not repairable and the manufacturer makes no recommendations for overhaul. If the alternator is found to be faulty, it must be replaced as an assembly. Likewise, if the regulator circuitry within the engine controller fails, the entire engine controller must be replaced as a unit. No repairs are recommended.