STORAGE BATTERIES. 



26l 



of wire in the winding, S, so that a very small variation of current 

 in 5 will produce the variations of voltage required to control 

 the storage battery. 



The differential booster. Fig. 1 5 1 shows an arrangement, 

 due to Mailloux, in which a booster, B, is actuated by variations 

 of line current. The booster has two opposing field windings, 

 5 and S' . When the demand for current is at its average value 

 the windings, 5 and S f , balance each other, the small generator, 

 B, develops no electromotive force, and the battery neither 

 charges nor discharges. When the line current is excessive the 

 winding, S, predominates, and the voltage of B helps the bat- 

 tery to discharge ; when, however, the line current is small the 

 winding, S' , predominates and the reversed voltage of B helps 

 the line voltage to charge the battery. 



Line 



* 



Fig. 152. 



Booster with automatic carbon rheostat control. Fig. 152 

 shows a carbon rheostat, RR' , connected across the terminals of 

 the storage battery, and the field winding, F, of the booster, B, 

 connected from the middle of the rheostat to the middle of the 



