What is the typical difference between a generator and an alternator on most aircraft?

• A. A generator provides AC power; an alternator provides DC power.
• B. Both generate DC power directly.
• C. Both generate AC power directly.
• D. A generator provides DC power; an alternator provides AC power that is rectified to DC.

Answer: (D)

The main idea is that aircraft electrical systems separate how the energy is produced from how it’s used. A generator in this context is a DC machine that puts out direct current directly to the aircraft’s DC bus. An alternator, on the other hand, generates alternating current and relies on rectification (diodes) to convert that AC into DC for the system. This is why the typical description is that a generator provides DC power, while an alternator provides AC power that is rectified to DC. The rectifier bank (often built into the alternator assembly) plus voltage regulation then keeps the DC bus at the proper 28 V (or similar) level.