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The electrical systems function is to generate and produce electrical power thought out the aircraft. The purpose of the electrically system is to provide power to the flight instruments, aircraft lighting, anti-icing and much more. The source of power is supplied by a few different types of sources:

  • Engine-driven alternating current (AC) generators

  • Auxiliary power units (APUs)

  • Or an external power source

In aviation, most airplanes electrical systems are built to either have a 12V (volt)battery and a 14V direct current (DC) system or 24V battery and a 28V (DC) system.

The components of the electrical systems of aircraft are:

  • Alternator / generator

  • Master switch

  • Battery

  • Bus bar

  • Fuses / circuit breakers

  • Ammeter

  • Voltage regulator

Alternator and generators

Alternators or generators are engine-driven components that supply electrical current to the aircraft electrical system; as well maintain an electrical change on the battery.

Alternators provide enough power to operate all the electrical systems even during slower engine speeds. The alternator produces alternating current (AC) current, which is converted into direct current (DC). Whereas most DC generators do not produce enough current at lower engine speeds (rpm).

Master Switch

The Master Switch can be turned “On” or “Off” and supplies electrical power to operate multiple circuits except the ignition system. The multiple circuits are:

  • exterior/interior lighting

  • Radio equipment

  • Turn Indicator (DC power)

  • Fuel gauges

  • Electric fuel pump

  • Stall warning

  • Pitot heat and starter.

​The Master switch can be designed as a split type of switch, when turning on the Master push both sides at the same time.

To separate the alternator switch, just the alternator side of the switch, this permits the pilot to exclude the alternator from the electrical system in the event of alternator failure.

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.


Electrical energy that is storied in the battery provides power to start the engine, as well as a limited source of electrical power to operator curtain systems in case the alternator or generator fails.

Aircraft batteries come in either a 12V (volt) or 24V.

Bus bar

In the aircraft you are flying for training such as a Cessna 150, C172, Piper Aircraft, etc. they are designed with two bus bars. One bus bar is the primary bus and the other is the avionics bus.

Bus bars are used as a terminal to simplify and organize the connections of the main electrical system to the different equipment using electrical power.

Fuses / circuit breakers

Fuses and or circuit breakers are designed to protect electrical systems from overloads. Circuit breakers and fuses are very similar in how the work, an advantage to the circuit breaker is that they can be reset.

  • ​Fuses are used on older aircraft.

  • Circuit breakers are used on new aircraft.

Placards are used to identify what equipment the circuit breaker is tired to.

The number stamped on each circuit breaker is to identify the amperage limit.


If a circuit break is tripped or popped out, it is okay to reset it after about a two-minute cool down. If the breaker trips a second time, it is a good idea not to rest it.


An Ammeter is used to monitor the aircrafts electrical system and shows if the alternator or generator is supplying adequate electrical power. It is also used to indicate if the battery is being charged.

If the needle is indicating on the positive side, the battery is being charged. whereas, if the needle is indicating a negative charge the electrical system is drawing for current from the battery.

If a full-scale negative indication is shown, then there is a malfunction of the alternator or generator. If there is a full-scale positive indication, is means there is a malfunction of the regulator.

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.

Voltage regulator

Are used to regulate the rate of charge to the battery by stabilizing the generator or alternators output. The output of either the generator or alternators output should be higher than voltage of the battery.

If the batter is 12-volts, the generator or alternator needs to be 14-volts to feed the battery.


The electrical systems are built to either have a 14V (volt) or 28V direct current (DC) system. Refer to the POH for the airplane you are flying.

The components of the electrical systems of aircraft are:

  • Alternator / generator

  • Master switch

  • Battery

  • Bus bar

  • Fuses / circuit breakers

  • Ammeter

  • Voltage regulator


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