3406E and 3456 Industrial Engines Systems Operation – Electrical System

Refer to the electrical system schematic in Electrical Schematic for the complete electrical system schematic of the 3406E and of the 3456. Refer to the electrical system schematic in Troubleshooting for another electrical schematic of the 3406E and 3456.

Grounding Practices
Proper grounding for the electrical system is necessary for proper vehicle performance and reliability. Improper grounding will result in unreliable electrical circuit paths and in uncontrolled electrical circuit paths.

Uncontrolled engine electrical circuit paths can result in damage to the main bearings, to the crankshaft journal surfaces, and to the aluminum components.

Uncontrolled electrical circuit paths can cause electrical noise which may degrade performance.

In order to ensure proper functioning of the electrical system, an engine-to-frame ground strap with a direct path to the battery must be used. This may be provided by a starter motor ground, by a frame to starter motor ground, or by a direct frame to engine ground. An engine-to-frame ground strap must be run from the grounding stud of the engine to the frame and to the negative battery post.

Illustration 1 g00433340
Typical example

Cylinder head to battery (“-“) ground

Illustration 2 g00433341
Typical example

Alternate cylinder head to battery (“-“) ground

The engine must have a wire ground to the battery.

Ground wires or ground straps should be combined at the studs that are only for ground use. The engine grounds should be inspected after every 250 hours. All of the grounds should be tight and free of corrosion.

All of the ground paths must be capable of carrying any potential currents. A wire that is AWG 0 or more is recommended for the cylinder head ground strap.

The engine alternator should be battery “-” ground with a wire size that is capable of managing the full charging current of the alternator.

The engine has several input components which are electronic. These components require an operating voltage.

This engine is tolerant to common external sources of electrical noise. Electromechanical buzzers can cause disruptions in the power supply. If electromechanical buzzers are used near the vehicle, the engine electronics should be powered directly from the battery system through a dedicated relay. The engine electronics should not be powered through a common power bus with other key switch activated devices. The engine electronics are the control group, the throttle position sensor, and “check engine” lamp.

Engine Electrical System
The electrical system can have three separate circuits. The three circuits are the charging circuit, the starting circuit, and the low amperage circuit. Some of the electrical system components are used in more than one circuit. The following components are common in each of the circuits: the battery, the circuit breaker, the ammeter, the cables from the battery and the wires from the battery.

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

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

The low amperage circuit and the charging circuit are connected through the voltmeter. The starting circuit is not connected through the voltmeter.

Charging System Components

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.

The 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 has many magnetic poles that are similar to fingers with air space between each opposite pole. The poles have residual magnetism that produces a small amount of magnet-like lines of force (magnetic field). This magnetic field is produced 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 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.

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.

Illustration 3 g00292313
Typical alternator components

(1) Regulator. (2) Roller bearing. (3) Stator winding. (4) Ball bearing. (5) Rectifier bridge. (6) Field winding. (7) Rotor assembly. (8) Fan.

Starting System Components


Illustration 4 g00292316
Schematic for a typical 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. 

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 has a solenoid. When the start switch is activated, the solenoid will move the starter pinion in order to engage the pinion and the ring gear on the engine flywheel. The starter pinion and the ring gear will engage before the circuit between the battery and the starter motor is closed by the electric contacts in the solenoid. When the circuit between the battery and the starter motor is complete, the pinion 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 will move away from the ring gear.

Illustration 5 g00292330
Typical cross section of a starter motor

(1) Field. (2) Solenoid. (3) Clutch. (4) Pinion. (5) Commutator. (6) Brush assembly. (7) Armature.

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