An alternator is a machine that generates an electrical signal from mechanical energy. The alternator may receive the mechanical energy in the form of a spinning shaft known as a rotor. The rotor may create a magnetic field that causes an electrical current to flow in a stationary portion of the alternator known as a stator. There are two main ways for a rotor to create a magnetic field to drive an electrical current in the stator. First, the rotor may contain a permanent magnet that creates a magnetic field that rotates with the rotor. Alternators that use a permanent magnet may be known as magnetos. Second, the rotor may create a magnetic field by having electric current pass through windings inside the rotor. The electric current passing through windings inside the rotor may be called an excitation current. In some examples, an alternator may include at least one permanent magnet and at least one excitation coil.
An alternator control device may be configured to control the excitation current traveling through the windings inside the rotor. In some examples, the alternator control device may be communicatively coupled to an engine control device that is configured to control an internal combustion engine that generates mechanical power for the alternator. The engine control device may transmit a voltage signal to the alternator control device, where the alternator control device controls the excitation current based on the voltage signal from the engine control device.