TM 10-3930-671-24 observing  the  area  to   the   left   of   the   zero   line   or   the reverse bias area, it can be seen that until the 10V point is reached, the Zener diode again acts electrically similar to a normal diode, in the reverse bias direction it will not allow current to flow.  The instant the voltage rises above 10 volts the Zener diode "breaks down", allowing current to flow.  The  ability  of  the  Zener  diode  to  "break  down", arid  then  heal  itself  as  the  voltage  swings  above  and below  the  avalanche  point  of  the  Zener  diode  is  utilized to   switch   the   associated   components   in   the   regulator "on"  and  "off,  switching  the  field  current  won"  and  "off, which in turn holds the system voltage to a predetermined value. THERMISTOR    -    Thermistor    (RT)    is    a    temperature sensitive     resistor,     in     the     regulator     voltage     divider network,  designed  to  provide  a  varying  resistance  with changes  in  regulator  temperature.    With  the  thermistor, the charging voltage is  automatically  in-  creased  slightly to    overcome    the    tendency    of    a    cold    battery    and electrolyte to resist the charging force. The thermistor will decrease charging voltage at higher temperatures as the warm   battery   and   electrolyte   will   accept   the   charging force at a lower charging voltage.  A typical temperature- resistance characteristic curve is shown in Figure No.7. FIGURE NO.  7 With the above information understood, the operation of the voltage regulator system will be easy to follow. (Figure No.  8). FIGURE NO.  8 SYSTEM    VOLTAGE  -  When  the  voltage  system  rises above a set value, the Zener diode (ZI) permits current to flow   in   the   base   of   the   driver   transistor   (Q1).      This causes transistor 01 to turn "on" and reverse bias output transistor 02, this in turn will turn "of’ the current applied to  the  alternator  field.    The  instant  the  system  voltage drops  below  the  predetermined  value,  the  Zener  diode stops    conducting.         When     the     Zener     diode     stops conduction,   forward   bias   is   removed   from   the   driver transistor 01 and it stops conducting.  This in turn allows Q2   to   begin   conduction,   allowing   field   current   to   be applied  to  the  altemator.    As  can  be  seen,  the  on-off effect of output transistor 02 is essentially that of a switch allowing alternator field current to be turned "on" and "off, to maintain a specific voltage. BATTERY INSTALLATION & CHARGING PRECAUTIONS CAUTION Observe proper polarity when installing  battery.  Ground  polarity  of battery and ground polarity of altemator, must be the same. Reverse    polarity     will     destroy     the rectifier   diodes   in   altemator.      As   a precautionary    measure,    disconnect positive  (HOT)  battery  terminal  when charging battery In vehicle. Connecting   charger   in   reverse   will destroy   the   rectifier   diodes   in   the altemator. TEST PRECAUTIONS - DO NOT, under any circumstances, short the field terminal of the altemator to ground,   as   permanent   damage   to   the   regulator   may occur. DO   NOT,   disconnect   the   voltage   regulator   while   the altemator   is   operating,   because   of   the   large   transient spike that occurs when disconnection takes place. permanent damage to the regulator will occur. F-274