14.3.
Charging Voltages
The main consideration in deciding the charging voltage is the battery terminal voltage when it is in fully charged condition. This value of charging voltage eliminates the risk of overcharging the battery and is infact a standard constant voltage charging technique. A charging voltage of 14 V is normally used for a nominal 12 V battery. Commercial vehicles generally use two batteries in series at a nominal voltage of 24 V and hence charging voltage for this system should be 28 V. These voltages are also used as the standard input for all vehicle loads. This chapter describes a 12 V system.
The expected voltage drops in the wiring of the charging circuit, and the operating temperature of the system and battery are the other factors to be considered when determining charging voltage. The operating temperature and voltage drop should be kept to a minimum. In reality the terminal voltage of the alternator may be slightly above the voltage supplied to the battery.
