STORAGE BATTERIES. 263 



tery to charge. In practice the current controlled by the rheo- 

 stat, RR f ', excites the field magnet of a very small auxiliary gen- 

 erator which delivers current to the field winding of the booster. 

 The loss of power in the rheostat, RR' ', is thus greatly reduced. 

 A general view of the automatic carbon rheostat, as manu- 

 factured by the Electric Storage Battery Company, is shown in 



Fig- 153- 



Example showing the equalizing effect of an automatically 



regulated storage battery upon the generator load in a street rail- 

 way plant. The ordinates of the extremely irregular curve in 

 Fig. 154 represent during an interval of ten minutes the fluctu- 

 ating demand for current at a typical railway power station. 

 Without a storage battery the generators would have to meet 

 this extremely irregular demand, varying from a minimum of 

 about 1 80 amperes to a maximum of about 850 amperes. The 

 ordinates of the slightly undulating dotted curve show the values 

 of generator output when an adequate storage battery is installed. 

 In this particular case the battery was regulated by a booster of 

 which the field excitation was under the control of a carbon 

 rheostat as shown in Fig. 152. When the total load curve is 

 above the dotted curve the battery discharges and when the total 

 load curve is below the dotted curve the battery charges. , 



The general average of the generator load must be slightly 

 greater than the general average of the station output inasmuch 

 as some energy is lost in the battery, but the average generator 

 load during a short period may be much greater or much less 

 than the average station output during the period. Thus the 

 average station output during the ten-minute run shown in Fig. 

 1 54 was evidently greater than the average generator load during 

 that time so that the battery was on the whole being discharged. 



Example of a storage battery and booster installation* A 

 power station supplies current at a constant electromotive force 



* An example of a large storage battery installation is described by Franklin E. 

 Moore in the Street Railway Journal for Sept. 21, 1901, " The Application of Storage 

 Batteries to the System of the Brooklyn Heights Railroad Company." 



