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Aircraft Electrical Systems

Circuit Basics​

Basic circuit

  • A circuits is a continuous path of current which carries an electrical potential.
  • Loads on a circuit can be connected in parallel or series
    • When in series, any disconnection of the circuit will cause all load to lose power
    • In contrast, a parallel circuit will all operations of the other loads

Diodes​

Diode symbol

  • Diodes are one-way gates for current

Aircraft Batteries​

  • Energy storage for starting and emergencies
  • Lead-acid batteries are common in aircraft

Alternators​

  • An alternator is connected to the crankshaft of the propeller and generates electrical power
  • An alternator will require a voltage regulator to normalize the voltage of the current before being passed to the battery or electrical busses
    • An over-voltage condition is usually displayed somehow in the cockpit

Ammeter and Load Meters​

  • Ammeter show battery and alternator output
    • When alternator is producing output, the ammeter will read positive
    • When the battery is being drawn, the ammeter will read negative
  • Load meters only show output from the alternator

Bus Bars​

  • A bus bar is common connection points for multiple electrical components
  • Typically there are several busses for different categories of electrical items

Master switch​

  • Master switch are often two-part switches
    • The left is the magneto master
    • The right is the battery master

Fuses and Circuit Breakers​

  • Fuses and circuit breakers are two methods of protecting individual circuits from overload
  • Circuit breakers can be reset after an overload condition is encountered
  • Fuses are consumable items, and extras should be carried

Solenoids, Relays, and Contactors​

  • A remote switch, which controls the open/closing of a separate circuit
  • You don't want the entire current of the master battery going through a small master switch
    • A solenoid or relay allows you to mount a small switch on the panel which controls a larger switch that actually closes the master circuit
  • Some small amount of electrical power is used to close a larger switch
  • These are often located on the airplane's firewall

Generators​

  • Coil of wire surrounding a magnets, mounted on a shaft
  • When the magnet spins inside the coils current is induced
  • Produces direct current output, but is dependent on the speed of the spinning shaft
  • Low RPM = Low voltage

Alternators​

  • Instead of a bar magnet on a shaft, an alternator uses an electromagnet
  • If the voltage is too low, it can regulate the magnetism of the electromagnet to be stronger
  • It outputs alternating current
  • A rectifier, usually attached to the back of the unit, converts this AC power into DC power for consumption