What is the primary source for APU control power on the C-130J?

The primary source for APU control power on the C-130J is the aircraft's battery. The APU, or Auxiliary Power Unit, requires power to operate its control systems, and this power primarily comes from the aircraft's main battery. The APU is responsible for providing electrical power, air conditioning, and engine starting capabilities, primarily when the main engines are not running.

Using the aircraft's battery ensures that there is sufficient electrical power available to control the APU without relying on external sources. This design choice is critical for the functionality and reliability of the APU in various operational scenarios, especially during ground operations or when the aircraft is parked.

While other sources like external power or backup generators can supply power to the aircraft's systems, they are not the primary source for APU control power. The main engines also do not provide direct power for APU operations but can be started by the APU if needed.