Electromagnetic Regulators

Figure 8-37. Field current is decreased as rotor speed increases, to keep AC generator (alternator) output voltage at a constant level.

Figure 8-38. The field current flows for longer periods of time at low speeds (t1) than at high speeds (t2).

(Reprinted by permission of Robert Bosch GmbH)

rotor speeds, the field current is reduced for long periods of time and is at full strength only for short periods (Figure 8-38B). This causes a low average field current.

On older vehicles, an electromagnetic regulator controlled the field circuit. However, in the 1970s, semiconductor technology made solid-state voltage regulators possible. Because they are smaller and have no moving parts, solid-state regulators replaced the older electromagnetic types in AC charging systems. On newer vehicles, the solidstate regulator may be a separate component built into the AC generator or incorporated into the powertrain control module (PCM).

Some solid-state regulators are mounted on the inside or outside of the AC generator housing. Remotely mounted voltage regulators often use a multiple-plug connector (Figure 8-40) to ensure all connections are properly made. This eliminates exposed wiring and connections, which are prone to damage.

Figure 8-39. Most regulators use a multiple-plug connector to ensure connections are properly made.

(Reprinted by permission of Robert Bosch GmbH)

Electromagnetic voltage regulators, sometimes called electromechanical regulators, operate the same whether used with old DC generators or more common AC generators. The electromagnetic coil of the voltage regulator is connected from the ignition switch to ground. This forms a parallel branch receiving system voltage, either from the AC generator output circuit or from the battery. The magnetic field of the coil acts upon an armature to open and close contact points controlling current to the field.

Double-Contact Voltage Regulator

At high rotor speeds, the AC generator may be able to force too much field current through a single-contact regulator and exceed the desired output. This is called voltage creep, or voltage drift. Single-contact regulators are used only with low-current-output alternators. Almost all electromagnetic voltage regulators used with automotive