As lights and other accessories are turned on and the load on the system increases, the current output to the circuits must be increased and the output voltage must be maintained.
The regulator again adjusts the rotor field circuit, but this time increases the current flow and therefore the magnetic field strength. The induced voltage in the stator rises to maintain system voltage and increase current output. There is no need for a current regulator as the design of the stator winding determines the maximum current output of the alternator at a system operating voltage of 13.8 to 14.2 volts.
If an alternator is rated at 40 amps it is capable of maintaining a system voltage of 13.8 to 14.2 volts up to a current load of 40 amps.
Background
The electrical power requirements within the current and future automobiles have been rising rapidly over the past few years and are expected to continue to rise. The trend is to replace engine-driven loads with electrically powered versions, and by the introduction of a wide range of new functionality in vehicles.
Cause and Effect
Electronics is playing an increasingly important role in all the various vehicle systems. Typical applications range from drivers for automotive actuators (i.e., relays, solenoids, lamps, heaters, motors, and ignition coils) to electric or hybrid drivetrains.
It is estimated that an average new vehicle has over 50 actuators, mostly controlled by power MOSFETs and other power semiconductor devices. The typical breakdown voltage ratings of power electronics in 14V, 28V, and 42V automotive power systems are all significantly higher than their specified maximum operating voltages.
The transients on the automobile power supply range from the severe, high-energy transients generated by the alternator/regulator subsystem to the low-level noise generated by the switching of inductive loads such as ignition coils, relays, solenoids, and DC motors. A typical automotive electrical system has all of these elements necessary to generate undesirable transients.
Source: CDX Global & Wikipedia - en.wikipedia.org
