TM 10-3930-671-24 CIRCUIT DESCRIPTION ALTERNATOR  -  The  alternator  produces  power  in  the form of three phase alternating current and voltage.  The alternating current is rectified to direct current by a three phase  full  wave  rectifier  circuit,  using  six  silicon  rectifier diodes.    Since  the  diodes  will  pass  current  in  only  one direction  (from  altemator  to  battery),  the  altemator  does not require the use of a cut out relay (Figures No.  5 and No.  5.1).    The  alternator  output  current  is  controlled  by the   current   flow   through   the   field   coil,   (rotor).      The amount of current required is determined and controlled by   the   regulator.      Since   there   is   very   little   residual magnetism  in  the  alternator,  it  is  necessary  to  supply  a small  amount  of  excitation  current  to  the  field  (rotor)  to start  the  process  of  current  generation.    The  excitation resistor  (Intemal  to  the  regulator),  supplies  this  starting current    when    the    ignition    is    turned    on.        Once    the alternator   is   excited,   a   voltage   is   developed   at   the regulator  input  terminal  and  the  voltage  regulator  takes over control of the system voltage. REGULATOR    (22/30     Amp     Systems)-     The     voltage regulator   is   a   standard   Prestolite   regulator.      A   coil operated reed switch is enclosed in the regulator housing and serves to sense regulator input voltage at a specific point,    usually    at    the    starter    or    battery    positive    (+) terminal.  The altemator output from the stator terminal of the alternator energizes the reed switch coil.  When the alternator is not charging, the reed switch is  open.    The  regulator  and  alternator  field  (rotor)  are disconnected  from  the  battery  (Figure  No.’s  5  and  5.1). Turning  the  ignition  (control)  switch   "on",   allows   initial field   (rotor)   activating   energy   to   flow   from   the   battery positive (+), through the ignition switch, to the  excitation resistor   and   charge   indicator   lamp,   through   the   input circuit  of  the  regulator  to  the  field  (rotor)  winding.    The reed  switch  is  by-passed  at  this  time  and  the  charge indicator lamp will glow. As   the   alternator   develops   a   charge,   part   of   the   AC component is sensed at the stator (STA) terminal of the alternator    and    is    conducted    through    a    diode    (coil rectifier),   in   the   regulator,   to   the   reed   switch   coil   to ground.  The magnetized coil turns the reed switch "on", connecting   the   regulator   input   directly   to   the   battery positive  (+)  terminal.    The  charge  indicator  lamp  will  be turned  off  due  to  equal  voltage  at  both  lamp  terminals. This   direct   sensing   technique   provides   a   true   battery voltage  to  the  regulator  and  is  not  subject  to  improper readings, due to circuit loss. REGULATOR     (45     Amp Systems)- The regulator basically acts as a multifunction circuit to operate.  It is a three part circuit:  1) Turn on (self-excited AC turn on, 2) Regulation, and 3) Lamp Driver Circuit. ALTERNATOR 22 / 30 Amp Systems with regulator FIGURE NO.  5 F-272