During APU start, which battery becomes isolated from the load buses?

During APU start, which battery becomes isolated from the load buses?

• A. Battery 2
• B. Battery 1
• C. Both batteries
• D. None

Answer: (B)

During APU start, the battery used to power the start circuit is kept separate from the load buses. This isolation protects the load buses from the high current surge of the starter and prevents backfeeding between batteries while the APU is not yet generating. In this system, Battery 1 is the one that becomes isolated from the load buses, while Battery 2 remains connected to the load buses to keep avionics and systems powered until the APU comes online. Once the APU is generating, the power can be shared across the buses and the isolation can be re-evaluated as normal operation resumes.

During APU start, the battery used to power the start circuit is kept separate from the load buses. This isolation protects the load buses from the high current surge of the starter and prevents backfeeding between batteries while the APU is not yet generating. In this system, Battery 1 is the one that becomes isolated from the load buses, while Battery 2 remains connected to the load buses to keep avionics and systems powered until the APU comes online. Once the APU is generating, the power can be shared across the buses and the isolation can be re-evaluated as normal operation resumes.