Principles of Operation of Charging System
A vehicle charging system has been represented in Fig. 14.2 as three blocks, i.e. the alternator, battery and vehicle loads. When engine is not running, the alternator voltage is less than the battery voltage so current flows from the battery to the vehicle loads and the alternator diodes prevent current flowing into the alternator. When engine is running, the alternator output is greater than the battery voltage, so current flows from the alternator to the vehicle loads as well as the battery. This implies that alternator output voltage must always be above the battery voltage during operation of the engine. However, the actual voltage used is critical and depends on a number of factors.