Overview
When the engine is running and voltage output is low, the regulator switches the rotor circuit to ground and maximum current flows through the rotor field winding. The high intensity magnetic field created raises the value of the induced voltage in the stator windings and alternator output rises. The output voltage is also impressed on the exciter diode circuit and the output voltage is sensed by the regulator control circuits via the regulator “L” terminal.
When the maximum allowable voltage has been reached, the control circuits switch the rotor field circuit off and the magnetic field at the pole shoes reduces in size, or “decays”. The decaying magnetic field reduces the magnitude of the voltage induced in the stator windings and lowers the alternator output voltage. This again is sensed by the voltage regulator control circuits and the rotor circuit is switched on once more.
The regulator switches rapidly between the ‘ON’ and ‘OFF’ conditions, within the pre-set maximum and minimum voltages, to allow the alternator to maintain an output voltage of approximately 14 volts and at the same time deliver the current needed for electrical system operation.
Functionality
Regulators
Early alternators used relays to regulate their output voltage much like those used on generators. When lower cost, more reliable solid state devices became available, electronic regulators became standard.
Although most regulators are factory set to force an alternator to produce 12 to 14 volts, they can be modified or new regulators custom built to provide almost any voltage up to 130 volts once their operation is understood. This is the case when an inverter is connected to the system.
When the alternator is running at low rpm, the alternator is putting maximum voltage and current into the rotor so that the alternator output voltage will come up to 12 volts. When the rpm starts to pick up so that the voltage starts to climb above 12, the regulator starts cutting back the voltage and current into the rotor. At very high rpm, the regulator is supplying the rotor with very little current, so that the output voltage remains at a constant 12 volts.
An electronic regulator provides continuous and instantaneous adjustment of rotor current by sampling the alternator output voltage and by comparing it against an internal standard reference. When output falls, a small current is sent to transistor B which amplifies it and sends it to transistor A which acts as a valve in controlling the heavy current flow from the battery to the rotor.
Input voltage to the regulator is usually a steady 12 volts whereas output to the rotor varies from zero to 12 volts to control rotor current. Many rotors-have a winding resistance of about 3 or 4 ohms, which causes a current of 3 to 4 amps to flow at 12 volts (calculated with Ohm's law).
Electronic regulators are superior to the old triple relay regulators used on generators. Obviously, there are no contacts to burn. While the older regulators would click in and out at the rate needed to hold output fairly steady, the solid-state regulators provides smooth quiet service, providing small continuous changes in rotor current. As long as the electronic unit kept cool, it should never need any service.
Alternator rotors are usually very rugged. Specially shaped poles create multiple magnetic poles from a single rotor winding.
Source: CDX Global & Wikipedia - en.wikipedia.org
