What is the function of the alternator in a bus electrical system?

• A. It charges the 12V battery and powers electrical loads while the engine is running.
• B. It converts DC to AC for accessories.
• C. It stores energy for future use when the engine is off.
• D. It reduces voltage for a 5V system.

Answer: (A)

The main idea is that the alternator provides all the electrical power the bus needs while the engine is running and keeps the battery charged. It takes mechanical energy from the engine and generates electrical energy, producing AC first and then rectifying it to DC to feed the 12V electrical system and recharge the battery. A voltage regulator keeps the system at about 13.8–14.4 volts so the battery stays properly charged and electronics stay stable. It doesn’t store energy—that’s the battery’s job—and it isn’t responsible for DC-to-AC conversion for general accessories or for reducing voltage to a 5V rail; those roles come from other components or downstream regulators.