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by Friday Morning Flight Plan at [date]
Most aircraft come with a display that shows voltage levels and ammeter readings. As you probably already know:
- Volts are how much electricity is in your system.
- Amps measure the force of the flow of those volts.
Electricity is kind of like a river: It has a certain volume of water (volts), and the water is moving at a certain rate (amps).
In an overvoltage condition, the voltage regulator is asleep at the alternator regulating wheel, and all the water (so to speak) pumps out at its maximum rate.
The ammeter pegs hard right, and the whole system (plus the battery) receives excessive current. TLDR: not good.
In an undervoltage condition, there's a near-certain chance that the alt field coil within the alternator has gone offline. Somehow, it lost its incoming current from the battery that energizes and creates the necessary magnetic field.
Without it, outgoing current from the alternator cannot be created.
What you can do
Some systems have pull-to-reset circuit breakers you can pull if shutting off the Alternator side of the Master switch doesn't remedy the overvoltage condition. Doing this kills the flow of current from the battery and shuts down the alt-field coil. Bingo! No more runaway juice coming out of the alternator.
Most systems have push-to-reset circuit breakers, and in an undervoltage condition, you'd want to check to see if the Alt or Alt Field circuit breaker(s) had popped. Convention says you should let them cool off for two minutes, reset them, and see if the flow of current from the battery re-energizes the alt field coil, which should bring the alternator back to life.
Some (but not all) aircraft come with high and low-voltage indicator lights, and in the case of much newer planes, visual annunciators are displayed on a digital read-out. It's essential that before each flight, you follow the checklist to ensure that verification of the working functionality of these warning displays has been determined.
If your aircraft has a generator, which comes with real magnets, there is no alt field coil, but you can still see a low voltage light come on sometimes during taxi because of low RPMs. You can make the low-voltage light go out by adding some power. Simple as that.
Ensure you check the ammeter on start-up, taxi, run-up, and climb-out, as well as regularly throughout your flight.
Some aftermarket checklists incorporate an "Alternator Check" step, where you recycle the Alternator side of the master switch and watch for an immediate drop in ammeter reading. You might want to ask your mechanic if doing this repeatedly is a good idea before making it a part of your routine because contacts can get worn down.
Lastly, ensure you know what the volts and amps should be for your plane in case you have to train in a different one during a lesson. Know what you should see, know where to look, and always use your checklist when troubleshooting.