Voltage Regulator

The alternator produces the electricity needed to charge the battery and to operate electrical equipment. Its output, however, continues to rise as its speed increases, so the charging system must be provided with a voltage regulator. Voltage regulators are in their third phase of development. First, there were electromagnetic voltage regulators, which were used in both dc and alternator charging systems. Then came electronic voltage regulators, which are still used in most late model applications. They are solid state devices, which did away with wire-wound coils, contact points, and bimetallic hinges. They appear to be more reliable, durable, and less affected by temperature change. Now, in some cars, the voltage regulator function has become part of the engine computer control system. Regardless of the kind, the voltage regulator controls voltage and current output of the alternator by automatically cutting resistance in or out of the field circuit to keep it in a safe value. Varying the resistance alters the amount of current passing through the field. When the battery becomes fully charged, the resistance is cut into the field circuit and the charging rate is decreased. Electromagnetic regulators, which are used on many dc generator charging systems, consist of three elements: cutout relay, current regulator, and voltage regulator. Others may use a cutout relay and a step-voltage control unit or a cutout relay with a vibrating voltage regulator or a combination of the cutout relay with a current-voltage unit. In electromagnetic regulators, the voltage regulator unit limits voltage output by controlling the amount of current applied to the rotating field. The field relay on these regulators connects the alternator field windings and voltage regulator windings directly to the battery. The conventional cutout relay unit has been eliminated by the diodes in the alternator. The current regulator has also been eliminated by the current-limiting characteristic of the alternator design. Basically, in a transistorized or an electronic regulator, the transistor is switched on and off to control the alternator field current. The frequency of switching depends on the alternator speed and accessory load, with the possibility that the on-off cycle may be repeated as often as 7000 times per second. The transistorized units have a voltage limiter adjustment. The electronic units are factory calibrated and sealed. They are also nonadjustable. When the ignition switch is turned off, the solid state relay circuit turns off the output stage, and turns off all current flow through the regulator. With that, there is no current drain on the battery. The field current overprotection stage protects the regulator against damage that could be caused by a "short" in the field circuit. Voltage regulator units have been replaced by functions with two engine computer modules on some late model Chrysler Corporation applications. The regulator functions are shared by circuits in the power and logic modules in the engine spark control computer. It is claimed that this prevents the possibility of "blowing" computer circuits if a charging system terminal is accidentally grounded. In operation, the field is turned on by a driver in the power module. The logic module also checks battery temperature as a means of determining and controlling alternator output voltage to control the amount of current allowed to pass through the alternator field windings.