Which statement is correct regarding DC generators or DC alternators?

The statement that the output must be equal to or higher than the battery voltage is correct because it reflects the operational requirements of DC generators and alternators when charging a battery. To effectively charge a battery, the voltage produced by the generator or alternator must exceed the battery's voltage. This allows for an effective flow of current into the battery, as it creates the necessary potential difference that drives electron flow into the battery cells.

When the output voltage is equal to the battery voltage, there is no driving force for current to flow into the battery. Therefore, having a higher output voltage is crucial for recharging purposes. This principle ensures that the electrical system can maintain battery health and full charge capacity, which is essential in various applications, including aviation.

The focus on the generator or alternator having a higher voltage is tied directly to its role in electrical systems, where it needs to provide power beyond what is used by the aircraft systems while also ensuring that the battery is charged effectively.