Regulation of Generator Output

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Regulation of Generator Output The fields of the generator depend upon the current from the armature of the generator for magnetization. Because  the  current  developed  by  the  generator increases  in  direct  proportion  to  its  speed,  the  fields become  stronger  as  the  speed  increases  and, correspondingly, the armature generates more current. The  extreme  variations  in  speed  of  the  automotive engine  make  it  necessary  to  regulate  output  of  the generator  to  prevent  excessive  current  or  voltage overload.  On  the  average  unit  of  CESE,  a  charging current in excess of 12 to 15 amperes is harmful to a fully charged battery if continued for too long. Regulators  are  of  two  types,  functioning  to regulate   either   voltage   or   current.   The   voltage regulator  regulates  the  voltage  in  the  electric  system and   prevents   excessive   voltage,   which   can   cause damage to the electric units and overcharge the battery. The  current  regulator  is  a  current  limiter;  it  prevents the generator output from increasing beyond the rated output of the generator. Regulation  of  voltage  only  might  be  satisfactory from  the  standpoint  of  the  battery;  however,  if  the battery  were  badly  discharged  or  if  a  heavy  electrical load were connected, the heavy current might overload itself  to  supply  the  heavy  current  demand.  Therefore, both current and voltage controls are used in a charging system. In most applications, a regulator assembly consists of   a   cutout   relay,   current   regulator,   and   voltage regulator  (fig.  2-13).  Each  unit  contains  a  separate core, coil, and set of contacts. The regulator assembly provides full control of the shunt-type generator under all  conditions.  Either  the  current  regulator  or  the voltage regulator may be operating at any one time, but in no case do they both operate at the same time. 2-13 When the electric load requirements are high and the battery is low, the current regulator will operate to prevent  the  generator  output  from  exceeding  its  safe maximum. In this case, the voltage is not sufficient to cause the voltage regulator to operate. But if the load requirements are reduced or the battery begins to come up to charge, the line voltage will increase to a value sufficient  to  cause  the  voltage  regulator  to  operate. When this happens, the generator output is reduced; it is  no  longer  sufficiently  high  to  cause  the  current regulator  to  operate.  All  regulation  is  then  dependent on   the   voltage   regulator.   Figure   2-14   shows   a schematic  wiring  diagram  of  a  typical  dc  charging circuit. In this circuit, two resistances are connected in Figure 2-13.—Regulator assembly with cover removed. parallel  into  the  generator  field  circuit  when  the  current regulator  points  open.  This  provides  a  low  value  of resistance, which is sufficient to prevent the generator output  from  exceeding  its  safe  maximum.  When  the voltage   regulator   contact   points   open,   only   one resistance  is  inserted  into  the  generator  field  circuit, and  this  provides  a  higher  value  of  resistance.  The voltage   regulator   must   employ   a   higher   resistance because   it   must   reduce   the   generator   output   as   it operates, and it requires more resistance to reduce the output  than  merely  to  prevent  the  output  from  going beyond the safe maximum of the generator. For  some  special  applications,  you  may  find  a combined  current-voltage  regulator.  In  this  case,  the regulators are combined in a single unit. The regulator assembly  will  consist  of  two  (regulator  and  circuit breaker) instead of three units. The   regulators   just   described   are   known   as electromagnetic   vibrating-contact   regulators.   The points on the armatures of the regulators may open and close as many as 300 times in one second to achieve the desired  regulation. The transistor type regulator is being used in late model equipment. This regulator has no moving parts. It  consists  of  transistors,  diodes,  condensers,  and resistors.  Some  models  have  two  filter  condensers, while others have only one. Adjustments  are  provided  on  some  types  of regulators and should be made only with the use of the manufacturer’s  instructions  and  the  recommended testing  equipment.  TRIAL  AND  ERROR  METHOD OF  REPAIR  WILL  NOT  WORK.

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