Electrics and electronics
Electrical questions cover the storage, generation, distribution and protection of power, plus the avionics that depend on it.
Generation and storage
Light aircraft use 14 V or 28 V DC systems. An alternator generates AC and rectifies it; a generator uses a commutator. A voltage regulator holds system voltage, and an over-voltage relay protects the avionics. The battery supplies starting current and emergency power; the ammeter shows charge or discharge. Master switch, battery contactor, starter relay and bus bar are the main distribution elements. Magnetos are not part of the electrical system and keep the engine running after an alternator failure.
Protection and avionics
Fuses and circuit breakers protect circuits; never reset a breaker more than the AFM allows. Bonding and static dischargers control static and lightning effects. Typical avionics: VHF COM (118–137 MHz), VOR/ILS, transponder, ELT and GPS.
Worked example
A 28 V alternator rated 70 A supplies 1,960 W. With avionics 8 A, landing light 10 A and pitot heat 5 A, load is 23 A. A 60 Ah battery would theoretically last 60 ÷ 23 = 2.6 h, but only about 80% is usable and voltage falls before the end, so plan on roughly 2 h or less and shed load.
Traps
Assuming the engine stops with the alternator; treating the ammeter as a battery charge gauge; resetting a tripped breaker repeatedly; forgetting that a 28 V system draws about half the current of a 14 V system for the same power; expecting the ELT to work without a serviceable battery.