![]() ![]() With it out of the picture, the field has no source of current and the alternator stops producing power. It senses voltage, and when it senses it’s too high, it disconnects the power from the regulator. There’s also the overvoltage unit generally connected in series, via the power wire to the regulator, between the alternator switch and the regulator. In many Cessna singles, this light is labeled “High/Low Volt.” In Pipers, it’s the “ALT” indicator. In general, when current flows from the battery, the regulator throws the alternator-out light. Read the aircraft POH carefully to understand what the panel annunciators are telling you. The regulator senses the alternator-out condition by determining whether current is going to, or coming from, the battery. It’s usually wired to the AUX terminal lug and triggers a warning light when voltage from the positive diode plate has dropped to a level that prevents the alternator from producing current. If you’re seeing occasional fluctuations that don’t feel right, something likely isn’t right.Īnd yes, there are sensors in the system that might fail, including the output sensor, or alternator-out sensor. ![]() One thing you might do-that many do not-is precisely set the limit warning in the engine monitor so it will get your attention during brief voltage excursions. In a practical sense, know where the voltage sits for your system and monitor it closely at all power settings and under different electrical loads. What’s normal regulated voltage? What’s listed in the service manual rules, but 13.75 to 14.5 volts on 14-volt systems and 27.5 to 28.5 volts on 24/28-volt systems is the desired range. Digital engine monitors are a good way to keep an eye on fluctuations in regulated voltage, but understand that you’re looking at bus voltage, which is further downstream. The regulator system senses the alternator voltage at a predetermined set point and adjusts the field current to keep the output voltage at the desired level. But alternator design for piston engines has changed little over the years, and voltage regulator issues remain common. Longer yet if you keep the battery on a charging tender. A charging system that keeps a constant (non-fluctuating) voltage across the battery usually makes for long battery life. When the alternator isn’t doing its job, there’s often a clue: You change batteries a lot. Once the battery does its job starting the engine, a healthy alternator keeps it charged, while powering the electrical system even at low engine RPM. But it’s complex enough that an unexpected failure can leave you stuck far from home, while failures in flight can be full-up emergencies.Įven if you don’t have the credentials and knowledge to tackle repairs on your own, there is some basic troubleshooting you can do to catch a failure early, while potentially saving some shop labor so your mechanic doesn’t have to start from scratch. The charging system on the typical GA aircraft isn’t exactly what we would call ultra-modern. ![]()
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