Fig. 1,185.—Variable resistance method of regulation for storage battery; diagram showing connections for charging two halves of a battery in parallel.
The connections for one of the simplest methods is shown in [fig. 1,185]. The battery is divided into two halves, which are connected in series for discharging and in parallel for charging. Since the voltage of each cell at the end of a discharge should not be lower than 1.8 volts, a battery intended for use on a 110 volt lighting circuit will require 110 ÷ 1.8 = 62 cells. The voltage necessary, however, for each cell at the end of a charge is about 2.6 volts, or a total of 2.6 × 62 = 161 volts for the battery, a value which is far above the line voltage. By dividing the battery into two halves and connecting them in parallel only 80.5 volts are necessary for charging. The excess voltage of the line, 29.5 volts is taken up by the resistance, which also controls the output of the battery on discharge.
End Cell Switches.—These may be used to advantage in small installations where there is not demand for current during the day, or where the charging is done by means of boosters.
Fig. 1,186.—Diagram of connections of a battery equipment for a residential lighting plant. In the diagram the voltmeter and voltmeter connections have been omitted. The bus bars on the battery panel are connected directly to the bus bars on the dynamo panel. In this installation the dynamos are run during the afternoon on discharge, being regulated by means of an end cell switch. On charge, the pressure above that of the bus bars, required to bring all cells up to full charge, is supplied by means of a motor driven charging booster, the voltage at the armature being suitably varied by changing the field excitation.
Ques. What is an end cell switch?
Ans. A form of switch employed in connection with a storage battery in order to control the end cells for regulating the voltage.