Generators in modern vehicles have developed overthe years into complex mini power plants. To ensure optimal voltage supply for the on-board electronics, precise control of the excitation current is required.
The generator, formerly also called the “dynamo,” supplies electrical consumers in the vehicle with power while the engine is running. In the past, this primarily concerned ignition, heating, or lighting, but today it is a wide range of electrical—and especially electronic—components and control units that require a stable voltage supply.
In the generator, the magnetic field required toproduce electricity is generated by an electricalexcitation coil. This makes it possible to keep theoutput voltage load constant across the entire enginespeed range.
In addition to the electrical load, temperature plays acrucial role in the precise regulation of the excitationvoltage. The generator’s output voltage is controlledwithin a temperature-dependent tolerance range—around 14 V for 12 V battery systems in passengervehicles, and correspondingly around 28 V for 24 Velectrical systems in commercial vehicles.
At colder temperatures, the voltage is regulated higherto optimally charge the vehicle battery—for example,during winter. Conversely, at higher temperatures, thevoltage is regulated lower to protect the battery andprevent overcharging.
Fuel consumption and the associated emissions arealso directly linked to the regulation of the generatorvoltage. By adjusting the excitation voltage to thecurrent operating conditions—such as ambienttemperature, engine load, electrical consumers, etc.—the power demand of the generator can be reduced tothe minimum necessary, keeping additional fuelconsumption as low as possible.
This requires close integration of the generator control with the engine management system to respond directly to various engine load phases. For example, the generator can be deactivated for a certain period during the start-up phase until the engine operation has stabilized. Accordingly, the generator voltage can be gradually readjusted during operation as electrical loads are switched on, allowing the engine to adapt to the additionally required torque.
In addition to purely electrical signal transmission, modernregulator modules are increasingly connected to the enginecontrol system via digital interface protocols such as BSS orLIN. This allows specific parameters, such as engine speed, to be transmitted directly, enabling the voltage regulator to respond immediately to rapid load changes and, for example, reduce power losses by lowering the generator voltage.
As an exposed component on the generator, the regulator issubject to particular challenges. Especially in the coldseason, the constant fluctuation between high operatingtemperatures in the engine compartment and low outsidetemperatures or cold splash water places great stress on it,negatively affecting the lifespan of the electroniccomponents. During the refurbishment of a generator, theregulator can therefore be replaced or its service lifeextended, for example, by installing new slip rings (carbonbrushes).
