An ammeter is used to monitor the performance of the aircraft  electrical system. The ammeter shows if the alternator/  generator is producing an adequate supply of electrical power.  It also indicates whether or not the battery is receiving an  electrical charge.  Ammeters are designed with the zero point in the center  of the face and a negative or positive indication on either  side.  [Figure 7-35]  When the pointer of the ammeter is  on the plus side, it shows the charging rate of the battery.  A minus indication means more current is being drawn  from the battery than is being replaced. A full-scale minus  deflection indicates a malfunction of the alternator/generator.  A full-scale positive deflection indicates a malfunction of  the regulator. In either case, consult the AFM/POH for  appropriate action to be taken.  Many aircraft are equipped with a battery switch that  controls the electrical power to the aircraft in a manner  similar to the master switch. In addition, an alternator switch  is installed that permits the pilot to exclude the alternator  from the electrical system in the event of alternator failure.  [Figure 7-33]  With the alternator half of the switch in the OFF position, the  entire electrical load is placed on the battery. All nonessential  electrical equipment should be turned off to conserve  battery power.  A bus bar is used as a terminal in the aircraft electrical system  to connect the main electrical system to the equipment using  electricity as a source of power. This simplifies the wiring  system and provides a common point from which voltage can  be distributed throughout the system.  [Figure 7-34]  Not all aircraft are equipped with an ammeter. Some have  a warning light that, when lighted, indicates a discharge in  the system as a generator/alternator malfunction. Refer to the  AFM/POH for appropriate action to be taken.  Another electrical monitoring indicator is a loadmeter.  Thi type of gauge has a scale beginning with zero and  shows the load being placed on the alternator/generator.  [Figure 7-35]  The loadmeter reflects the total percentage of  the load placedon the generating capacity of the electrical  system by the electrical accessories and battery. When all  electrical components are turned off, it reflects only the  amount of charging current demanded by the battery.  Fuses or circuit breakers are used in the electrical system to  protect the circuits and equipment from electrical overload.  Spare fuses of the proper amperage limit should be carried in  the aircraft to replace defective or blown fuses. Circuit breakers  have the same function as a fuse but can be manually reset,  rather than replaced, if an overload condition occurs in the  electrical system. Placards at the fuse or circuit breaker panel  identify the circuit by name and show the amperage limit.  A voltage  regulator controls the rate of charge to the battery  by stabilizing the generator or alternator electrical output. The  generator/alternator voltage output should be higher than the  battery voltage. For example, a 12-volt battery would be fed  by a generator/alternator system of approximately 14 volts.  The difference in voltage keeps the battery charged.  There are multiple applications for hydraulic use in aircraft,  depending on the complexity of the aircraft. For example, a  hydraulic system is often used on small airplanes to operate  wheel brakes, retractable landing gear, and some constant- speed  propellers. On large airplanes, a hydraulic system is  used for flight control surfaces, wing flaps, spoilers, and  other systems.  basic hydraulic system consists of a reservoir, pump  (either hand,  ele ctric, or engine-driven), a filter to keep the  fluid clean,  selector valve to control the direction of flow,  relief valve to relieve excess pressure, and an actuator.  [Figure 7-36]  Figure 7-33.  On this master switch, the left half is for the alternator  and the right half is for the battery.  7-31  Hydraulic Systems •  Electric fuel pump  •  Stall warning system  •  Pitot heat  •  Starting motor 