Final answer:
The subject question relates to the function of main and APU batteries during the startup of an APU. The main battery controls the ECU, while the APU battery powers the starter motor. Automotive examples illustrate how battery configurations impact the delivery of voltage and current for starting engines.
Step-by-step explanation:
The question pertains to the electrical systems involved in the operation of an Auxiliary Power Unit (APU), particularly focusing on the battery configurations and their functions during the start-up process of the APU. The main battery is responsible for controlling the Electronic Control Unit (ECU) of the APU, which is essentially the brain behind the APU's operation ensuring it functions correctly. The operation of the APU battery is mainly to provide the power required to turn over the starter motor, initiating the start of the APU. This distinction is important to understand as the batteries are designed to perform specific roles in the system.
Drawing a parallel from automotive battery systems, we see that different battery configurations can affect the startup performance. For instance, in diesel trucks, two 12-V batteries are often used in parallel to provide the sufficient current needed to start a larger diesel engine, keeping the voltage the same but increasing the available current. Conversely, connecting batteries in series would increase the voltage, which could lead to many problems including difficulties in starting the engine due to the potentially incorrect voltage for the application.
The significance of this discussion is understanding that while voltages of batteries may be the same, it's the energy and current delivery capability that determines their suitability for a specific task. A vehicle's battery must be capable of supplying a large current briefly to start the engine, after which the vehicle's alternator assumes the role of supplying electrical power for running the vehicle and recharging the battery. As energy is consumed, a battery's terminal voltage may drop, as observed when headlights dim due to a depleted battery.