DC alternators are excited by what source?

• A. Self-excited
• B. Battery or Externally
• C. Permanent Magnet
• D. Buffer from Bus

Answer: (B)

DC excited alternators need a DC current in the field winding to create the magnetic field that induces voltage. That excitation current comes from an external DC source—usually the aircraft battery or another external power source routed through the regulator—to startup and then maintain regulation. The regulator modulates this field current to keep the output at the correct level. Using residual magnetism to self-excite isn’t how these units are typically started, and permanent-magnet designs don’t require DC excitation at all. That’s why the excitation source is described as coming from a battery or externally supplied power.