Question 111Electricity & Electronics - 1st Asst/Chief

70% to pass

When a self-excited alternator's field has lost its residual magnetism due to a prolonged idle period, it will fail to produce a voltage. Flashing the field is the procedure used to restore the residual magnetism. Using a 12 volt storage battery, how is this performed?

AThe S+ and S- leads are disconnected from the alternator stator. The S+ lead is connected to the positive terminal of the battery, and the S- lead is connected to the negative terminal.

BThe F+ and F- leads are disconnected from the alternator field. The F+ lead is connected to the positive terminal of the battery, and the F- lead is connected to the negative terminal.

CThe F+ and F- leads are disconnected from the alternator field. The F+ lead is connected to the negative terminal of the battery, and the F- lead is connected to the positive terminal.

DThe S+ and S- leads are disconnected from the alternator stator. The S+ lead is connected to the negative terminal of the battery, and the S- lead is connected to the positive terminal.

AI Explanation

The correct answer is B. To restore the residual magnetism of a self-excited alternator's field that has lost it due to a prolonged idle period, the field must be "flashed" using a 12-volt battery. This is done by disconnecting the F+ and F- leads from the alternator field, then connecting the F+ lead to the positive terminal of the battery and the F- lead to the negative terminal. This allows a current to flow through the field windings, which re-magnetizes the field and restores the residual magnetism. The other options are incorrect because they either disconnect the wrong leads (the stator leads instead of the field leads) or connect the leads to the wrong battery terminals, which would not properly flash the field and restore the residual magnetism.

Want to practice with timed exams?

Download Coast Guard Exams for the full exam experience.

Get the App