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 or storage tank, storing (in chemical form) the energy originally produced by the engine-driven A.C. generator (alternator). 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 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 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, through belts, by the engine crankshaft. It consists of two coils of fine wire, 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. In an alternator, the field rotates while all the current produced passes only through the stator windings. The brushes bear against continuous slip rings. 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. Alternators are self-limiting as far as maximum current is concerned.
Observing these precautions will ensure safe handling of the electrical system components, and will avoid damage to the vehicle's electrical system:
- Be absolutely sure of the polarity of a battery before making connections. Connect the cables positive to positive, and negative to negative. Connect positive cables first and disconnect negative cables first.
- Disconnect both vehicle battery cables before attempting to charge a battery.
- Never ground the alternator output or battery terminal. Be cautious when using metal tools around a battery to avoid creating a short circuit between the terminals.
- Never run an alternator without load unless the field circuit is disconnected.
- Never attempt to polarize an alternator.