TM 1-1510-223-10 system   and   mission   avionics   is   supplied   by   two   DC powered three phase mission inverters (fig.  2-30). The   mission   ACIDC   power   cabinet   (fig.      2-31)   is located  in  the  mission  rack,  aft  of  the  copilot's  seat  AC power    may    be    applied    through    an    external    power receptacle  located  on  the  underside  of  the  left  wing,  just outboard of the engine nacelle. 2-73. DC POWER SUPPLY. One    nickel-cadmium    battery    furnishes    DC    power when  the  engines  are  not  operating.    This  24-volt  34- ampere/hour   battery,   located   in   the   right   wing   center section,  is  accessible  through  a  panel  on  the  top  of  the wing.    DC  power  is  produced  by  two  engine-driven  28 volt,     400-ampere     starter-generators.          Controls     and indicators   associated   with   the   DC   supply   system   are located  on  the  overhead  control  panel  (fig.    2-13)  and consist of a single battery switch, two generator switches, two DC digital voltmeters, and two DC digital loadmeters. a. Battery  Switch  A  switch,  placarded  BATTERY  - OFF/RESET - ON (fig.  2-13), is located on the overhead control  panel  under  the  MASTER  SWITCH  (gang  bar). The  BATTERY  switch  controls  DC  power  to  the  aircraft bus system through the battery relay, and must be ON to allow  external  power  to  enter  aircraft  circuits.    When  the MASTER     SWITCH     (gang     bar)     is     placed     aft,     the BATTERY switch is forced OFF. NOTE With battery or external power removed from the   aircraft   electrical   system   due   to   fault, power  cannot  be  restored  to  the  system  until the BATTERY switch is moved to OFF/RESET, then ON. b. Generator  Switches.    Two  switches  (fig.    2-13), placarded  GENERATOR  #  1  and  #  2  are  located  on  the overhead control panel.  These switches control electrical power from the designated generator to paralleling circuits and   the   bus   distribution   system.      Switch   positions   are placarded   RESET,   ON,   and   OFF.      RESET   is   forward (spring loaded back to ON), ON is center, and OFF is aft. When a generator is removed from the aircraft electrical system,     due     either     to     fault     or     from     placing     the GENERATOR  switch  in  the  OFF  position,  the  affected unit  cannot  have  its  output  restored  to  aircraft  use  until the GENERATOR switch is moved to RESET, then ON. c. Master Switch.  All  electrical current may be shut off  using  the  MASTER  SWITCH  gang  bar  (fig.    2-13) which extends above the battery and generator switches. The MASTER SWITCH (gang bar) is moved forward when  a  battery  or  generator  switch  is  turned  on.    When moved   aft,   the   bar   positions   each   switch   to   the   OFF position. d. DC  Load  and  Voltmeters.    Four  digital  meters, located on the overhead control panel (fig.  2-13), display voltage readings and show the rate of current usage from the left and right generating systems.  The two loadmeters indicate  output  amperage  as  a  percent  of  rated  capacity from  the  respective  generator.    Current  consumption  is indicated   as   a   percentage   of   total   output   amperage capacity  for  the  generating  system  being  monitored  The two   voltmeters   indicate   bus   voltage   for   the   respective generating system e. Battery Volt/Ammeter.   The mission control panel (fig.  4-1), located in the fuselage sidewall adjacent to the copilot's  seat,  incorporates  a  digital  volt/  ammeter  that displays available battery voltage and amperage. Minimum battery voltage for engine starting is 22 VDC. f. Battery Charge Monitor.   Nickel-cadmium  battery overheating   will   cause   the   battery   charge   current   to increase if thermal runaway is imminent The aircraft has a charge-current  sensor  which  will  detect  a  charge  current The charge current system senses battery current through a shunt in the negative lead of the battery.  Any time the battery charging current exceeds approximately 7 amperes  for  6  seconds  or  longer,  the  amber  BATTERY CHARGE    annunciator    and    the    MASTER    CAUTION annunciator  will  illuminate.    Following  a  battery  engine start, the caution annunciator will illuminate approximately six seconds after the generator switch is placed in the ON position.    The  annunciator  will  normally  extinguish  within two    to    five    minutes,    indicating    that    the    battery    is approaching a full charge.  The time interval will increase if   the   battery   has   a   low   state   of   charge,   the   battery temperature  is  very  low,  or  if  the  battery  has  previously been discharged at a very low rate (i.e., battery operation of  radios  or  lights  for  prolonged  periods).    The  caution annunciator  may  also  illuminate  for  short  intervals  after landing    gear    and/or    flap    operation.        If    the    caution annunciator  should  illuminate  during  normal  steady-state cruise, this indicates that conditions exist that may cause a  battery  thermal  runaway.    if  this  occurs,  the  battery current  should  be  monitored  using  the  battery  ammeter. If  battery  current  continues  to  increase,  the  battery  is  in thermal runaway and should be selected OFF and may be turned   back   ON   only   for   gear   and   flap   extension   and approach to landing. g. Generator Out Warning Annunciators.  Two caution/advisory    annunciator    panel    fault    annunciators inform  the  pilot  when  either  generator  is  not  delivering current     to     the     aircraft     DC     bus     system.          These annunciators are placarded #1 DC GEN and #2 DC GEN. Illumination 2-64