3412E and C30 Marine Engines Caterpillar

Engine Electrical System

The electrical system has three separate circuits.

• the charging circuit

• the starting circuit

• the low amperage circuit

Some of the electrical system components are used in more than one circuit. The following items are common in each of the circuits.

• the battery

• the circuit breaker

• the ammeter

• the cables

• the wires for the battery

The charging circuit is in operation when the engine is running. An alternator makes electricity for the charging circuit. A voltage regulator in the circuit controls the electrical output in order to keep the battery at full charge.

The starting switch is in operation only when the start switch is activated.

The electrical systems include a Diagnostic Connector. The Diagnostic Connector is used to test the charging circuit. The Diagnostic Connector is also used to test the starting circuit.

The low amperage circuit and the charging circuit are connected to the same side of the ammeter. The starting circuit connects to the opposite side of the ammeter.

Charging System Components

Alternators

4N-3986 Alternator

4N-3987 Alternator

Illustration 1	g00530109
(1) Rectifier. (2) Rotor assembly. (3) Stator winding. (4) Coil and support assembly. (5) Ball bearing. (6) Regulator. (7) Roller bearing. (8) Fan.

The alternator is driven by the crankshaft pulley through a belt that is a Poly-vee type. This alternator is a three-phase self-rectifying charging unit. The regulator is part of the alternator.

This alternator design has no need for slip rings or for brushes. The only part of this alternator that moves is the rotor assembly. All of the conductors that carry current are stationary. The following components are the conductors: the field winding, the stator windings, six rectifying diodes and the regulator circuit.

The rotor assembly contains many magnetic poles. These magnetic poles look like fingers with air space between each of the opposite poles. The poles have residual magnetism that is similar to permanent magnets. Permanent magnets produce a small amount of magnetic lines of force (magnetic field) between the poles.

As the rotor assembly begins to turn between the field winding and the stator windings, a small amount of alternating current (AC) is produced in the stator windings. The alternating current is produced from the small magnetic lines of force that are created by the residual magnetism of the poles. The AC is changed into direct current (DC) when the current passes through the diodes of the rectifier bridge. Most of this current provides the battery charge and the supply for the low amperage circuit. The remainder of the current is sent to the field windings. The DC current flow through the field windings (wires around an iron core) increases the strength of the magnetic lines of force. These stronger magnetic lines of force increase the amount of AC that is produced in the stator windings. The increased speed of the rotor assembly also increases the current output of the alternator and the voltage output of the alternator.

Regulators

3T-6354 Regulator

7T-5665 Regulator

Illustration 2	g00360155
Regulator assembly

The voltage regulator is a solid-state electronic switch. The voltage regulator senses the voltage of the system. The regulator then uses switches to control the current to the field windings. This controls the voltage output in order to meet the electrical demand of the system.

Alternator

6T-1395 Alternator

Illustration 3	g00530110
(1) Rotor assembly. (2) Stator assembly. (3) Brush assembly. (4) Regulator. (5) Bearings. (6) Capacitor. (7) Slip rings.

The alternator is driven by the crankshaft pulley through a belt that is a Poly-vee type. The regulator is part of the alternator. The alternator is made up of the following components:

• the head assembly

• the rotor assembly

• the stator assembly

• the rectifier

• heat removal assemblies

• the brush and holder assembly

• the regulator

The rotor assembly has the field windings. The field windings are wires around an iron core. The field windings create magnetic lines of force when direct current (DC) flows through the windings. As the rotor assembly begins to turn, the magnetic lines of force are broken by the stator. This creates an alternating current (AC) in the stator.

The rectifier has diodes which change the alternating current (AC) from the stator to direct current (DC). Most of this current accomplishes these two activities:

• The current charges the battery.

• The current supplies the low amperage circuit.

The remainder of the direct current (DC) is sent to the field windings through the brushes.

Regulator Kit

134-8278 Regulator Kit

Illustration 4	g00530253
134-8278 Regulator Kit

The voltage regulator is a solid-state electronic switch. The voltage regulator senses the voltage of the system. The regulator then uses switches to control the current to the field windings. This controls the voltage output in order to meet the electrical demand of the system.

Starting System Components

Solenoid

A solenoid is an electromagnetic switch that performs two basic functions:

• The solenoid closes the high current starter motor circuit with a low current start switch circuit.

• The solenoid engages the starter motor pinion with the ring gear.

Illustration 5	g00292316
Typical solenoid schematic

The solenoid has windings (one set or two sets) around a hollow cylinder. A plunger with a spring load device is inside of the cylinder. The plunger can move forward and backward. When the start switch is closed and electricity is sent through the windings, a magnetic field is created. The magnetic field pulls the plunger forward in the cylinder. This moves the shift lever in order for the pinion drive gear to engage with the ring gear. The front end of the plunger then makes contact across the battery and across the motor terminals of the solenoid. The starter motor then begins to turn the flywheel of the engine.

When the start switch is opened, current no longer flows through the windings. The spring now returns the plunger to the original position. At the same time, the spring moves the pinion gear away from the flywheel.

When two sets of windings in the solenoid are used, the windings are called the hold-in winding and the pull-in winding. Both of the windings wind around the cylinder for an equal amount of times. The pull-in winding uses a wire with a larger diameter in order to produce a stronger magnetic field. When the start switch is closed, part of the current flows from the battery through the hold-in winding. The remainder of the current flows through the pull-in windings, to the motor terminal, and then to the ground. When the solenoid is fully activated, the current is shut off through the pull-in windings. Only the smaller hold-in windings are in operation for the extended period of time that is necessary for the engine to be started. The solenoid will now take a smaller amount of current from the battery. Heat that is created by the solenoid will be kept at an acceptable level.

Starter Motor

The starter motor rotates the engine flywheel at a rate that is fast enough to start the engine.

The starter motor contains a solenoid (2). When the start switch is activated, the solenoid (2) will move the starter pinion (4). Then, this starter pinion (4) engages the ring gear on the flywheel of the engine. The starter pinion (4) engages with the ring gear before the electric contacts in the solenoid (2) close the circuit between the battery and the starting motor. When the circuit between the battery and the starter motor is complete, the starter pinion (4) will rotate the engine flywheel. A clutch provides protection for the starter motor so that the engine cannot turn the starter motor too fast. When the switch is released, the starter pinion (4) will move away from the ring gear.

Illustration 6	g00292330
Starter motor cross section (1) Field. (2) Solenoid. (3) Clutch. (4) Starter pinion. (5) Commutator. (6) Brush assembly. (7) Armature.

Magnetic Switch

A magnetic switch (relay) is used sometimes for the starter solenoid circuit. The magnetic switch has the same electrical properties as the solenoid. The magnetic switch reduces the current load on the start switch. Also, the magnetic switch controls current to the starter solenoid.

Other Components

Circuit Breaker

The circuit breaker is a switch that opens the battery circuit if the current in the electrical system is higher than the rating of the circuit breaker. The metal disc (2) is activated by heat. If the current in the electrical system gets too high, the metal disc will get hot. This heat causes a distortion of the metal disc. A circuit breaker that is open can be reset when the metal disc becomes cooler. Push the reset button (1) in order to close the contact points and reset the circuit breaker.

Illustration 7	g00281837
Circuit breaker schematic (1) Reset button. (2) Disc in open position. (3) Contacts. (4) Disc. (5) Battery circuit terminals.