What voltage is necessary to start the APU?

What voltage is necessary to start the APU?

• A. 25 V
• B. 28 V
• C. 24 V
• D. 50 V

Answer: (A)

Starting the APU requires a stable DC supply at the voltage the APU start circuit is designed to use. For this aircraft, that designated start voltage is 25 volts DC. This voltage level is chosen to match the APU starter motor and control circuitry ratings, ensuring the starter can engage properly and the APU control logic can power up reliably. If a lower voltage were applied, the starter might not spool the APU correctly; if a higher voltage were applied, it could stress or damage the start circuit and related electronics. The other options (lower or higher voltages) aren’t the specified start voltage for the APU on this airplane, which is why 25 V is the correct choice.

Starting the APU requires a stable DC supply at the voltage the APU start circuit is designed to use. For this aircraft, that designated start voltage is 25 volts DC. This voltage level is chosen to match the APU starter motor and control circuitry ratings, ensuring the starter can engage properly and the APU control logic can power up reliably. If a lower voltage were applied, the starter might not spool the APU correctly; if a higher voltage were applied, it could stress or damage the start circuit and related electronics. The other options (lower or higher voltages) aren’t the specified start voltage for the APU on this airplane, which is why 25 V is the correct choice.