BATTERIES 



all made up by appropriate series and parallel connections of relatively few 

 types of cell. There are some two dozen common types of cylindrical cells 

 and about the same number of layer cells. We shall not give performance 



Cake of depolarizer 



Plastic band, 

 shrunk on, to 

 hold cell together 



Paper soaked 

 in electrolyte 



Figure 19.1 



Duplex electrode; 

 a Zinc plate coated 

 with carbon on 

 lower side 



figures for all the cylindrical cells but content ourselves with one of the 

 largest (Bell cell), the smallest (D21, hearing aid cell) and two popular 

 intermediate sizes, the U2 and the UIO. The latter size of cell is used in the 

 older pattern HT and grid bias batteries — very useful in laboratory work 

 because of the choice of voltages provided by the tapping points*. The 

 cylindrical cells are shown in Plate 19.1 and the layer cells in Plate 19.2. 



Dry cells — Initial current to endpoint of M V. 



Duty ratio — 4 hours in 24. 



With this information we can construct two further tables. Taking the 

 average voltage per cell on discharge to be 1-3. 



Approximate Energy Delivered per Unit Volume (Wh/in') 



* We also consider 4 important sizes of larger cell, designated by the Ever Ready 

 Company types 112, 132, 135 and 155. 



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