1488 THE BELL SYSTEM TECHNICAL JOURNAL, NOVEMBER 1953 

 50 



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40 



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30 



25 



20 



15 



4000 8000 12,000 16,000 20,000 24,000 



HOURS OF OPERATON 



Fig. 11 — • Forward aging characteristics of various suppliers 26-volt cells. 



33-volt cells for several years. Again, there is a wide difference in the 

 rate of aging in the various manufacturers' products. 



Continued aging tests on stacks made by manufacturer "E" show that 

 after 21,000 hours of continuous operation, the forward voltage drop has 

 increased only 8 per cent. Extrapolation of these data indicate a life 

 expectancy of thirty years. 



It should be emphasized that the data on the 33-volt cells, with the 

 one exception, were taken on experimental stacks obtained from various 

 companies while they still were in the research and development stages 

 of processing the 33-volt cell. Undoubtedly, further development pro- 

 grams on this type of cell will result in improved aging qualities. 



Fig. 13 shows clearly what happens to the aging rate as manufacturers 

 attempt to increase still further the voltage rating. These data are based 

 upon 26-, 33- and 40- volt cells made by one supplier who is commercially 

 produ(;ing cells with these ratings. The aging rate is accelerated greatly 

 as the voltage rating is increased. 



All the foregoing aging data were taken on stacks operated at rated load 

 currents. A longer operating life may be expected if selenium stacks are 

 selected to operate at lower load currents. As shown in Fig. 14, the aging 



