Once you get a few hours into your flight training, you quickly realize the role of the alternator and battery, if you weren’t already familiar with their basic operation. Airplanes, like most vehicles, also have a voltage regulator installed as part of the aircraft’s electrical system.
Voltage regulators are small, fairly simple electrical boxes that are mounted somewhere near the engine, sometimes on the firewall. As the name suggests, they regulate the voltage that comes out of the alternator so that the airplane’s electrical equipment gets a constant level of volts.
An aircraft alternator is basic in the sense that it doesn’t know how much load is being drawn from its output. That’s where the voltage regulator comes in. So if you turn on a landing light, for example, the regulator will allow more current to come through, stabilizing the system at the necessary voltage. The regulator also supplies a constant voltage to the battery to ensure it’s charging properly.
Voltage regulators can incorporate a number of other features, such as overvoltage protection. With this feature, the regulator knows when the alternator starts to put out too much voltage, at which point it will trip a circuit breaker and save the electrical system from possible damage.
Modern voltage regulators are solid state, meaning they have no moving parts to break. Older designs were electro-mechanical, but they’re rarely found anymore. Because they are solid state, the modern voltage regulator is incredibly reliable. But when they do fail, the symptoms are easy to spot. Since voltage is no longer metered in this case, the airplane’s ammeter will fluctuate greatly, and usually show too high of a charge. It may also manifest itself as a reduction in electrical power and, eventually, a dead battery.
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