SELENIUM RECTIFIER APPLICATION 



>ii)i;katioN8 



I i 



For operation in ambient temperatures above -f 35°C, the voltage or 

 current ratings, or both must be reduced to limit the cell temiKTuture 

 (ambient plus heat rise) to -f-75°C. The de-rating factors for voltage and 

 current vary somewhat from supplier to supplier, but Fig. 2 shows typical 

 de-rating curves for operation of selenium stacks above a +35*'C am- 

 bient. 



Selenium rectifiers can be operated at cell temperatures above TS^C, 

 but aging accelerates with temperature and ex(^essive temperatures will 

 result in rapid failure. 



A special problem today is the application of selenium rectifiers for 

 high temperature military uses. Many military projects are requesting 

 designs to operate at ambient temperatures of +70 to -}-90°C. Unfor- 

 tunately very little data about rectifier operation and life expectancy 

 under these conditions have been obtained up to now. 



VOLTAGE 



CURRENT CHARACTERISTICS 



To demonstrate the non-linear characteristics of selenium rectifier 

 cells, Fig. 3 illustrates representative dynamic voltage-current curves 

 showing the open circuit and short circuit characteristics of bridge con- 

 nected stacks composed of various cell sizes rated at 26 volts, rms. This 

 rating was chosen since all manufacturers presently are producing cells 

 of this type. 



Cells with higher voltage ratings generally have a slightly greater for- 

 ward voltage drop. 



Table II — DC Output Ratings 



CeU Size 



y2'' 



V X 



2" X 



V X 



5'' X 



h" X 



Dia. . . 

 Dia. . . 



X IW- 



xVAr 



2" .. .. 



z\. . 



Dia. . 



h" 



x6''.. 

 6*.. .. 



Area 

 Square Inches* 



0.049 



0.196 



0.56 



1.1 



1.7 



3.1 



7.0 

 12.5 

 21.2 

 21.2 

 26.2 



Continuous DC Amps at +3S*C 



Single-Phase 



' Three- 

 Phaae 



HaU 



0.006 



0.025 



0.090 



0.175 



0.270 



0.500 



1.10 



2.00 



3.40 



3.40 



4.20 



Iridce 

 CJ. 



0.012 



0.050 



0.18 



0.35 



0.54 



1.0 



2.2 



4.0 



6.8 



6.8 



8.4 



Approximate active rectifying area (varies with suppliers) 



Bridfe 



0.018 



0.075 



0.270 



0.525 



0.810 



1.50 



3.30 



6.00 



10.2 



10.2 



12.6 



