controllers.  Electric  brakes  are  used  to  bring  a load  to  rest,  or  to  hold  it  at  rest,  when  electric power  to  the  motor  is  cut  off.  Aboard  ship, electric  brakes  are  used  primarily  on  hoisting  and lowering equipment such as cranes, winches, and windlasses. Most  controllers  function  simply  to  start  or to stop auxiliary machinery; but, some controllers also  provide  for  reversal  of  direction  or  multispeed operation.  Motor  controllers,  sometimes  called starters,  have  overload  protective  devices  to prevent burning out the motor. Most controllers cut  out  automatically  when  the  electric  power fails, and they have to be restarted manually. This type  of  motor  controller  is  called  a  low-voltage protection  (LVP)  controller.  Another  type  of motor  controller,  which  is  used  primarily  with vital loads, is called a  low-voltage  release  (LVR) controller.  The  LVR  controller  disconnects  the motor   from   the   supply   voltage   if   the   supply voltage drops below a predetermined level. When the supply voltage returns to a normal level, the LVR controller automatically restarts the motor. BATTERIES Aboard ship, batteries are one of the sources for   emergency   and   portable   power.   Storage batteries  are  used  to  power  emergency  equipment, ship’s boats, and forklifts. The storage battery is also  used  as  a  source  of  energy  for  emergency diesel generators, gyrocompasses, and emergency radios. You  should  be  familiar  with  safety  precautions you must follow when you work around batteries. Batteries must be protected from salt water, which can  mix  with  the  electrolyte  (the  acid  solution) and  release  poisonous  gases.  Salt  water  in  the electrolyte also sets up a chemical reaction that will ruin the battery. If a battery is exposed to salt water,  notify  the  electric  shop  immediately. Storage  batteries,  when  being  charged,  give  off a   certain   amount   of   hydrogen   gas.   Battery compartments   should   be   well   ventilated   to discharge this gas to the atmosphere. WARNING Flames or sparks of any kind, including lighted  cigarettes,  should  never  be  allowed in the vicinity of any storage battery that is being charged. When  the  battery  is  in  a  low  or  discharged state and does not perform properly, you should notify  the  Electrician’s  Mate  (EM). PORTABLE  ELECTRICAL EQUIPMENT Aboard   ship,   you   will   perform   many   jobs using  small,  portable  electrical  tools.  Because portable  electrical  tools  are  commonly  used  under a variety of conditions, they are subject to damage and abuse. The  Navy  has  a  good  electrical  tool  safety program. This program is carried out by qualified EMs. However, EMs can only make safety checks on   tools   that   are   brought   to   their   attention. Electrical  handtools  should  be  inspected  before each use to make sure the power cord is not nicked or  cut,  and  the  plug  is  connected  properly. Electrical  handtools  should  be  turned  in  to  the electricians as prescribed by the electrical safety program. BATTLE  LANTERNS Relay-operated  hand  lanterns  (fig.  12-11,  view A), usually called battle lanterns, are powered by dry-cell batteries. Hand lanterns are provided to give emergency light when the ship’s service and emergency/alternate lighting systems fail. These lanterns  are  placed  in  spaces  where  continual illumination   is   necessary,   such   as   machinery spaces,  control  rooms,  essential  watch  stations, battle dressing stations, and escape hatches. All auxiliary machinery with gauge boards should be provided with a battle lantern to illuminate the gauge  board  in  the  event  of  a  casualty.  The battle  lantern  should  not  be  removed  from  its mounting bracket except in an emergency.  Do not use it as a flashlight in nonemergency situations. The  relay  control  boxes  for  battle  lanterns  are connected  to  the  emergency  lighting  supply circuit (or to the ship’s service lighting circuit) in which  the  lantern  is  installed.  If  power  in  the circuit  fails,  the  relay  opens  and  the  batteries energize the lantern. Relay-operated battle lanterns are capable of operating for a minimum of 10 hours before the light  output  ceases  to  be  useful. Similar  hand  lanterns  (fig.  12-11,  view  B), which are not connected to relays, are installed throughout  the  ship  to  provide  light  in  stations 12-12