SELENIUM RECTIFIER APPLICATION CONSIDERATIONS 1471 



arrangements for series, parallel or series-parallel connection of the ceUfl 

 as required. 



The completed assembly is designated as a rectifier stack. A rectifier 

 stack is a single structure of one or more rectifier (!ells. 



Small size cells (less than 1") have no center hole for mounting. These 

 cells are assembled without spacer washers in glass, metal, phenol fibre 

 or bakelite tubing. Terminal leads extend outside these enclosures. 



SYMBOLIC NOTATION 



The combination of cells on a stack is described by a sequence of four 

 symbols written a-b-c-d with the following significances:* (a) number 

 of rectifying elements; (b) number of cells in series in each rectifying ele- 

 ment; (c) number of cells in parallel in each rectifying element; and (d) 

 symbol designating circuit or stack connections. 



The symbols for the more common types of stack assemblies are shown 

 schematically in Fig. 1. 



A basic selenium stack is defined as a stack having a single selenium 

 cell in each rectif3dng element. For instance, a 4-1- IB stack is a basic 

 full-wave single-phase bridge rectifier stack with one selenium cell in 

 each of the four rectifying elements. 



The total number of selenium cells on any stack is the product of the 

 three numbers indicated. For example, a single-phase full-wave bridge 

 stack with three cells in series and two cells in parallel per rectif3dng ele- 

 ment would be designated as a 4-3-2B stack assembled with 4X3X2 

 or 24 cells. 



"H" HALF-WAVE STACK "D" DOUBLER STACK "C" CENTER TAP STACK 



ONE RECTIFYING ELEMENT TWO RECTIFYING ELEMENTS TWO RECTIFYING ELEMENTS 



1-1-lH 2-1-lD 2-1-IC 



OR 

 AC AC 



'B" SINGLE-PHASE FULL-WAVE STACK "B" 30 FULL- WAVE STACK 



FOUR RECTIFYING ELEMENTS SIX RECTIFYING ELEMENTS 



4-1-1B 6-1-IB 



- AC + AC - I AC AC I AC + 



Fig. 1 — Stack assembly sjTnbols. Color coding of terminals (AIEE and 

 NEMA Standard) : yellow for ac, red for plus dc output, and black for negative dc 

 output. 



* This method of specifying stack assemblies has been standardized by both 

 the National Electric Manufacturer's Association and the American Institute 

 of Electrical Engineers. 



