What is the minimum voltage required before starting the APU?

• A. 12 volts
• B. 22 volts
• C. 24 volts
• D. 28 volts

Answer: (B)

Starting the APU requires enough electrical power to energize the starter motor and its control circuitry. 22 volts is the threshold at which the starter solenoid and the APU start sequence can reliably engage. If the supply falls below this, the starter won’t pull in and the APU won’t crank. Voltages at or above 22 volts will allow the APU to start, with 24 or 28 volts simply being higher—but still within a normal operating range. A voltage like 12 volts is not enough to drive the starter or the control electronics.