is  indicated  as  a  percentage  of  total  output  amperage capacity   for   the   generating   system   monitored. e. Battery  Volt-Amp  Meter.  The  mission  con- trol  panel  (fig.  4-l),  located  on  the  right  inside  fuse- lage sidewall adjacent to the copilot’s seat, has a bat- tery-amperage  meter  that  displays  battery  voltage  on the  left  side  of  the  meter  and  battery  current  on  the right  side  of  the  meter.  Minimum  battery  voltage  for engine  start  is  22  VDC. f.   Battery   Monitor.   Nickel-cadmium battery overheating  will  cause  the  battery  charge  current  to increase   if   thermal   runaway   is   imminent.   The   air- craft  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   yellow   BATTERY   CHARGE   annuncia- tor  light  and  the  master  fault  caution  light  will  illu- minate.  Following  a  battery  engine  start,  the  caution light  will  illuminate  approximately  six  seconds  after the  generator  switch  is  placed  in  the  ON  position. The  light  will  normally  extinguish  within  two  to  five minutes,  indicating  that  the  battery  is  approaching  a full  charge.  The  time  interval  will  increase  if  the  bat- tery  has  a  low  state  of  charge,  the  battery  tempera- ture 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  cau- tion   light   may   also   illuminate   for   short   intervals after  landing  gear  and/or  flap  operation.  If  the  cau- tion   light   should   illuminate   during   normal   steady- state   cruise,   it   indicates   that   conditions   exist   that may  cause  a  battery  thermal  runaway.  If  this  occurs, the  battery  switch  shall  be  turned  OFF  and  may  be turned  back  ON  only  for  gear  and  flap  extension  and approach  to  landing.  Battery  may  be  used  after  a  15 to  20  minute  cool  down  period. g.   Generator   Out   Warning   Lights.   Two  cau- tion/advisory   annunciator   panel   lights   inform   the pilot  when  either  generator  is  not  delivering  current to  the  aircraft  DC  bus  system.  These  lights  are  plac- arded  No.1  DC  GEN  and  No.2  DC  GEN.  Illumina- tion   of   the   two   MASTER   CAUTION   lights   and either   fault   light   indicates   that   either   the   identified generator   has   failed   or   voltage   is   not   sufficient   to keep  it  connected  to  the  power  distribution  system. The  GPU  shall  be  adjusted  to 28  volts  maximum  to  prevent the   aircraft. regulate  at damage   to TM   55-1510-221-10 h.   DC   External   Power   Source.   External  DC power   can   be   applied   to   the   aircraft   through   an external   power   receptacle   on   the   underside   of   the right  wing  leading  edge  just  outboard  of  the  engine nacelle.  The  receptacle  is  installed  inside  of  the  wing structure  and  is  accessible  through  a  hinged  access panel.  DC  power  is  supplied  through  the  DC  exter- nal  power  plug  and  applied  directly  to  the  battery bus  after  passing  through  the  external  power  relay. Turn  off  all  external  power  while  connecting  the power   cable   to,   or   removing   it   from,   the   external power  supply  receptacle.  The  holding  coil  circuit  of the  relay  is  energized  by  the  external  power  source when  the  BATT  switch  is  in  the  ON  position.  The GPU  shall  be  adjusted  to  regulate  at  28  volts  maxi- mum  to  prevent  damage  to  the  aircraft  battery. i. Security  Keylock  Switch,  The aircraft has a security  keylock  switch  (fig.  2-12)  installed  on  the overhead   control   panel,   placarded   OFF   -   ON.   The switch  is  connected  to  the  battery  relay  circuit  and must   be   ON   when   energizing   the   battery   master power  switch.  The  key  cannot  be  removed  from  the lock  when  in  the  ON  position. j. Circuit  Breakers.  The   overhead   circuit breaker  panel  (fig.  2-26)  contains  circuit  breakers  for most   aircraft   systems.   The   circuit   breakers   on   the panel  are  grouped  into  areas  which  are  placarded  as to   the   general   function   they   protect.   A   DC   power distribution   panel   is   mounted   beneath   the   aisleway floor  forward  of  the  main  spar.  This  panel  contains higher  current  rated  circuit  breakers  and  is  not accessible  to  the  flight  crew  under  normal  condi- tions. 2-75. AC POWER SUPPLY. a.  Single  Phase  AC  Power  Supply.  AC   power for  the  aircraft  is  supplied  by  inverter  units,  num- bered No. 1 and No.2 (fig. 2-23) which obtain opera- tional   current   from   the   DC   power   system.   Both inverters  are  rated  at  750  volt-amperes  and  provide single-phase  output  only.  Each  inverter  provides  115 volt  and  26  volt,  400  Hz  AC  output.  The  inverters are  protected  by  circuit  breakers  mounted  on  the DC   power   distribution   panel   beneath   the   aisleway floor.  Controls  and  indicators  of  the  AC  power  sys- tem  are  located  on  the  overhead  control  panel  and on   the   caution/advisory   annunciator   panel. ( 1 . )   A C   P o w er WARNING/CAUTION Lights.  Illumination   of   the   two   MASTER   CAU- TION  lights  and  the  illumination  of  an  annunciator caution  light  No.1  INVERTER  or  No.2  INVERTER indicates   an   inverter   failure. (2.)   Instrument   AC   Light.   A  red  warning light   and   two   MASTER   WARNING   lights   located 2-65