Fig. 1,196.—Diagram showing usual connections of a non-reversible shunt booster and battery system. In charging, the switches A and B are closed, and C put on contact m; the end cell switch D is put on the last contact. Part of the dynamo current will go into the line and part through the booster into the battery. The charging current is adjusted by the field rheostat E. To discharge, throw the end cell switch D to first contact; next turn switch C to contact s. The battery is then in parallel with the dynamo with all end cells cut out. As the voltage of the battery falls, end cells are cut in by the end cell switch D.
Ques. How may it be used reversibly?
Ans. It will give a pressure to assist the battery to discharge when excited from the bus bars and provided with a reversing rheostat.
In this case it will assist the battery to discharge when the direction of the field magnetization is changed. When so used, no end cells are necessary, but the booster must be run continuously during the entire period of discharge.
Ques. What should be the battery capacity on a 110 volt circuit with a reversible booster?
Ans. 56 cells will be sufficient.
The voltage to fully charge is 56 × 2.6 = 146, or 36 volts above dynamo voltage. Minimum voltage of discharge = 1.8 × 56 = 100 volts, or 10 volts less than that of the line. Hence, the booster need give only 36 volts maximum, and is required to add 10 volts to the battery voltage toward the end of battery discharge. In this case, the booster voltage is only 36/49 or about ¾ of that required in the preceding case; five cells less of battery are necessary and the end cell switches and leads are eliminated.
