The main function of a regulator assembly is to maintain a consistent voltage level, regardless of variations in the bus's engine speed or electrical load. It achieves this by monitoring the voltage output from the bus's alternator and adjusting the field current to control the alternator's output voltage.

Here is a description of the components and functions typically found in a bus regulator assembly:

1. Regulator: The regulator is the central component of the assembly. It consists of electronic circuitry that measures the output voltage of the alternator and adjusts the field current accordingly to maintain a constant voltage. The regulator may utilize various control methods, such as electromechanical or solid-state technology, to achieve voltage regulation.

2. Sensing Circuit: The regulator assembly includes a sensing circuit that measures the bus's electrical system voltage. It provides feedback to the regulator, allowing it to make adjustments as necessary.

3. Field Control: The regulator assembly controls the field current of the alternator. By adjusting the field current, it regulates the magnetic field strength, which, in turn, controls the alternator's output voltage. Increasing or decreasing the field current adjusts the output voltage to maintain a stable voltage level.

4. Protection Features: The regulator assembly often includes protection features to safeguard the electrical system and components. These features may include over-voltage protection, which prevents excessive voltage from damaging sensitive electronics, and over-current protection, which protects against excessive current draw.