Contact point voltage regulator, mounted away from the alternator in the engine compartment

Electronic voltage regulator, mounted away from the alternator in the engine compartment

Electronic voltage regulator, mounted on the back or inside the alternator

The contact point voltage regulator uses a coil, set of points, and resistors that limits system voltage. The electronic or solid-state regulators have replaced this older type. For operation, refer to the "Regulation of Generator Output" section of this chapter.

The electronic voltage regulators use an electronic circuit to control rotor field strength and alternator output. It is a sealed unit and is not repairable. The electronic circuit must be sealed to prevent damage from moisture, excessive heat, and vibration. A rubber like gel surrounds the circuit for protection.

An integral voltage regulator is mounted inside or on the rear of the alternator. This is the most common type used on modern vehicles. It is small, efficient, dependable, and composed of integrated circuits.

An electronic voltage regulator performs the same operation as a contact point regulator, except that it uses transistors, diodes, resistors, and capacitors to regulate voltage in the system. To increase alternator output, the electronic voltage regulator allows more current into the rotor windings, thereby strengthen the magnetic field around the rotor. More current is then induced into the stator windings and out of the alternator.

To reduce alternator output, the electronic regulator increases the resistance between the battery and the rotor windings. The magnetic field decreases and less current is induced into the stator windings.

Alternator speed and load determines whether the regulator increases or decreases charging output. If the load is high or rotor speed is low (engine at idle), the regulator senses a drop in system voltage. The regulator then increases the rotors magnetic field current until a preset output voltage is obtained. If the load drops or rotor speed increases, the opposite occurs.

Alternator Maintenance
Alternator testing and service call for special precautions since the alternator output terminal is connected to the battery at all times. Use care to avoid reversing polarity when performing battery service of any kind. A surge of current in the opposite direction could bum the alternator diodes.

Do not purposely or accidentally "short" or "ground" the system when disconnecting wires or connecting test leads to terminals of the alternator or regulator. For example, grounding of the field terminal at either alternator or regulator will damage the regulator. Grounding of the alternator output terminal will damage the alternator and possibly other portions of the charging system.

Never operate an alternator on an open circuit. With no battery or electrical load in the circuit, alternators are capable of building high voltage (50 to over 110 volts) which may damage diodes and endanger anyone who touches the alternator output terminal.

Alternator maintenance is minimized by the use of prelubricated bearings and longer lasting brushes. If a problem exists in the charging circuit, check for a complete field circuit by placing a large screwdriver on the alternator rear-bearing surface. If the field circuit is complete, there will be a strong magnetic pull on the blade of the screwdriver, which indicates that the field is energized. If there is no field current, the alternator will not charge because it is excited by battery voltage.

Should you suspect troubles within the charging system after checking the wiring connections and battery, connect a voltmeter across the battery terminals. If the voltage reading, with the engine speed increased, is within the manufacturer's recommended specification, the charging system is functioning properly. Should the alternator tests fail, the alternator should be removed for repairs or replacement. Do NOT forget, you must ALWAYS disconnect the cables from the battery first.