Lead-Acid-Battery Charger

Modern sealed lead-acid batteries are simplicity itself in use. In contrast to NiCd batteries, they may be charged by connecting them to a constant voltage (at the correct level). The charging cur- rent then gives a pretty good indication of the state of charge. These batteries may also be charged at a rapid rate, as long as the charging cur- rent is limited at the onset of the charg- ing process. Dependent on the make, a charging current of several times one tenth of the capacity in Ah is permiss- ible. For instance, a 5 Ah battery may be charged with an onset charging current of 1 A. The charging voltage may then be 2.45 V per cell. At such a (relatively) high voltage, the current has to be limited, otherwise the onset charging current through a flat battery may be as high as 10 A. The proposed charger, whose circuit is shown in Fig. 1, incorporates a "stan- dard" voltage regulator, IC1, and a vari- able current limiter consisting of Ti, 111, and R4. As soon as the current throu...