All About Aircraft Electrical Systems

Responsible for running the lights, avionics, engine starter motor, and much more, aircraft electrical systems are essential to the proper function of an array of devices. When the engine is not running, the electrical system is powered by a battery. When the engine is started, an alternator or DC generator offers a continuous supply of electricity to power the various electrical components and charge the battery. Because the battery has a finite capacity, the aircraft must be self-sufficient in terms of its electrical requirements.

The battery circuit and alternator circuit feed electrical current to all electrical components via a busbar that establishes a common distribution channel. Meanwhile, the battery is attached to a master switch that feeds battery power directly to the busbar when turned on. For example, if the master switch is turned on, electrical energy will route from the battery to the beacon through the busbar.

Generally, the battery is connected to the engine starter motor, and it is used to turn the engine over when starting. Prior to starting the engine, all avionics built into the aircraft must be shut off to accommodate for the large current being drawn to the starter motor, ensuring there is no damage to navigation equipment and radios. Some avionics are wired to a separate busbar that can be turned on and off using an avionics master switch, but if these parts are not wired to a common box, each component should be manually switched off before starting.

Alternators use the principle of electromagnetic induction to create a constant supply of electricity when the engine begins to run. The electricity generated is routed to the busbar where it feeds into the electrical systems and powers the components that operate during flight. Simultaneously, the alternator charges the battery while the engine runs, and a Direct Current (DC) system is used to power the electric parts on the aircraft. More than that, the alternator produces an Alternating Current (AC) and is converted to DC using a rectifier before entering the busbar.

The cockpit features an ammeter or loadmeter, with the former displaying the current flow into or out of the battery. Furthermore, the ammeter has a zero point in the center of the dial, and a negative and positive charge indication on either side. This means that when the current provides a positive reading, the generation system is charging the battery. Adversely, when the current provides a negative reading, this indicates that the battery is discharging. In other words, more current flows into the battery than can be replaced by the alternator. As such, an ammeter will first show a high rate of charge (positive reading) as the battery is recharged once the engine starts, and it will decrease gradually as the battery reaches full charge.

A loadmeter, on the other hand, has a scale that starts at zero, displaying the output of the alternator. It shows the sum of the load required to run the active electrical components and the load needed to charge the battery. If the alternator fails, the battery would run the electrical components until the charge is depleted. If a generator failure is detected, it is important to turn off all non-essential electrical components to conserve battery life. Moreover, it is important to terminate the flight as soon as possible if this occurs.

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