SELENIUM RECTIFIER APPLICATION CONSIDERATIONS 



1485 



0.8 



0.6 



0.4 



0.2 



Fig. 9 — Dynamic forward voltage drop per cell. 



forward rms voltage drop per cell (DV) obtained from Fig. 9 is 1.10 volts 

 at 100 per cent normal rated current. From the formulas in Table III, 

 the input voltage is: 



Eac = l.loEdc + 2nDV, 

 Eac = 1.15 X 48 + 2 X 



2 X 1.1 = 59.6 volts rms. 



This input voltage is required for a new or unaged stack. Since the 

 stack ages under service operating conditions, additional input voltage 

 will be required to maintain the original dc output. It is considered good 

 practice to design for a 100 per cent increase in the initial forward voltage 

 drop (DV) of the stack. The aged stack, then would require 



Eac = 1.15^^c + 2(2nDF), 



Eac = 1.15 X 48 + 2(2 X 2 X 1.1) = 63 volts rms. 



The amount by which an increase of 100 per cent in the forward volt- 

 age drop or forward resistance will change the output is dependent upon 

 the design of the circuit. It depends upon the ratio in per cent of the for- 

 ward rectifier stack resistance to the total circuit resistance including 



