SELENIUM RECTIFIER APPLICATION CONSIDERATIONS 



1487 



100 



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Q 90 



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YEARS 



Fig. 10 — Forward aging characteristics of 18-volt cells. 



10 



assembled with cells rated at 18 volts rms are shown in Fig. 10.* After 10 

 years (approximately 90,000 hours) continuous operation, the forward 

 drop on one supplier's product increased approximately 90 per cent. A 

 second supplier's product increased 100 per cent in 3 years under similar 

 operating conditions. Further development programs by each manu- 

 facturer resulted in improved aging qualities as indicated by tests made 

 on stacks obtained at a later date. 



By introducing changes in their manufacturing techniques, the in- 

 dustry eventually increased the voltage ratings to 26 volts rms per cell. 

 This change in processing, however, raises the question — how has the 

 operatinglifebeenaffected? Fig. 11* clearly illustrates that although many 

 manufacturers are commercially producing 26-volt cells, the life ex- 

 pectancy is vastly different. 



In order to save space, weight and critical materials, manufacturers 

 are attempting to produce cells with still higher voltage ratings. Most 

 companies have had a 33-volt cell development program under way for 

 some tune, but again the problem of aging must be considered. Fig. 12* 

 compares the forward aging of 26- and 33-volt cells after 5,000 hours 

 operation. It is evident that in all cases except one, the 33-volt cells age 

 substantially faster than the 26-volt cells. The exception is manufacturer 

 "E" who has not produced 26-volt cells but has commercially processed 



* The designations A, B, C, etc. shown on all aging curves are not *« be in- 

 terpreted to represent the same manufacturer's product on each of the figures. 



