What is the minimum allowable battery voltage for APU operation?

The minimum allowable battery voltage for APU (Auxiliary Power Unit) operation in the C-130J is crucial for ensuring that the APU can start and function effectively. A voltage of 22 VDC is required because it provides sufficient power for ignition, operation of the starter motor, and the overall functionality of the APU system. Operating the APU at voltages lower than this threshold could lead to inadequate performance, potential failures to start, or malfunctioning systems, as the required current draw would exceed what the lower voltage can reliably supply. Therefore, a minimum of 22 VDC is established as a standard to guarantee reliable APU operation and to support the electrical demands of various aircraft systems that depend on it during ground operations and engine start-up.