STORAGE BATTERIES. 



259 



the storage battery. Any great demand for current causes the 

 voltage, E, to decrease, so that the battery can discharge, and 

 when the demand for current is small the voltage, E, rises and the 

 battery is charged. A battery connected as shown in Fig. 149 



Long feeder 



Fig. 149. 



is called a floating battery. Such a floating battery cannot com- 

 pletely equalize the demand on the station, inasmuch as the rise 

 and fall of the voltage, E, depends upon some decrease and increase 

 of the current flowing through the long feeders. 



The negative booster. It frequently happens that a small gen- 

 erating plant in a modern office building supplies current for 

 lighting and also for operating an elevator motor. The lamps 

 require constant voltage and the motor operates most satisfactorily 

 if provision is made for a great decrease in voltage when the motor 

 starts and takes excessive current In this case the voltage, E v 

 at the lamps may be kept nearly constant, and a large delivery 

 of current to the elevator motor may be made to cause a great 

 decrease in the voltage, E 2 , see Fig. 1 50, by interposing an auxiliary 



Lamps 



Fig. 150. 



