Which circuit provides energizing current for the alternator's magnetic field?

• A. Ignition switch circuit
• B. Battery charging circuit
• C. AC generation circuit
• D. DC circuit

Answer: (D)

The magnetic field in the alternator is energized by a direct current in the field winding. This field current comes through the DC field circuit, usually from the aircraft battery via the voltage regulator. With a steady DC field established, the rotor acts like a magnet; as it spins, its changing magnetic field induces alternating current in the stator windings, which is then regulated and rectified for the electrical system. The ignition switch circuit powers the ignition system, not the alternator’s field. The AC generation circuit refers to producing the AC output from the already-excited field. So the energizing current for the alternator’s magnetic field is provided by the DC circuit.