1490 THE BELL SYSTEM TECHNICAL JOURNAL, NOVEMBER 1953 



90 



a" 

 O 



80 



o 

 a. 



1 70 



a. 

 o 

 u. 



_! 60 



5 

 O 



^40 



z 



UJ 

 O 30 



20 



10 



4000 6000 



HOURS OF OPERATION 



8000 



10,000 



Fig. 13 — Forward aging versus cell voltage rating. 



room temperatures. It is readily evident that at 4-80°C ambient (1) the 

 forward aging rate is increased (2) the different manufacturers' stacks 

 age at different rates and (3) there is no definite correlation of the aging 

 rate with normal operation at room temperature. As previously men- 

 tioned under room temperature operation, longer life can be expected if 

 stacks are operated at reduced current loads. At 80°C ambient however, 

 three of the four manufacturers' stacks aged as much at half load as at 

 full load. 



CONCLUSIONS 



The development and use of selenium rectifier stacks in this country 

 has been quite rapid in the last ten years. The voltage ratings per cell 

 have increased from 14 volts rms to 26 and 33 volts on a commercial 

 basis. The trend in the selenium industry seems to indicate that cell 

 voltage ratings will be further increased. 



The proper selection and procurement of selenium rectifier stacks and 

 their application to dc power supplies for large scale industrial or military 

 projects usually require considerably more information than can be ob- 

 tained from published data in manufacturers' catalogs. Considerable 

 differences have been observed in the performance of similar stacks 



