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 cables
- The wires for the battery
- The ammeter
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.
| NOTICE |
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The disconnect switch, if so equipped, must be in the ON position to let the electrical system function. There will be damage to some of the charging circuit components if the engine runs with the disconnect with in the OFF position. |
If the engine has a disconnect switch, the starting circuit can operate only after the disconnect switch is put in the "ON" position.
The starting switch is in operation only when the start switch is activated.
The low amperage circuit and the charging circuit is connected through the ammeter. The starting circuit is not connected through the ammeter.
Charging System Components
| NOTICE |
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Never operate the alternator without the battery in the circuit. Making or breaking an alternator connection with heavy load on the circuit can cause damage to the regulator. |
Alternator
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| Illustration 1 | g00293544 |
Alternator components (typical example) (1) Brush holder (2) Rear frame (3) Rotor (4) Stator (5) Drive end frame (6) Fan assembly (7) Slip rings (8) Rectifier | |
The alternator has three-phase, full-wave, rectified output. The alternator uses brushes to generate electricity.
The alternator is an electrical component and a mechanical component that is driven by a belt from engine rotation. The alternator is used to charge the storage battery during engine operation. The alternator is cooled by a fan that is a part of the alternator. The fan pulls air through holes in the back of the alternator. The air exits the front of the alternator and the air cools the alternator in the process.
The alternator converts mechanical energy and magnetic energy into alternating current (AC) and voltage. This process is done by rotating an electromagnetic field (rotor) that is direct current (DC) inside a three-phase stator. The alternating current and the voltage that is generated by the stator are changed to direct current. This change is accomplished by a system that uses three-phase, full-wave, rectified outputs. The three-phase, full-wave, rectified outputs have been converted by six rectifier diodes that are made of silicon. The alternator also has a diode trio. A diode trio is an assembly that is made up of three exciter diodes. The diode trio rectifies field current that is needed to start the charging process. Direct current flows to the alternator output terminal.
A solid-state regulator is installed in the back of the alternator. Two brushes conduct the current through two slip rings to the field coil on the rotor.
Also, a capacitor is mounted in the back of the alternator. The capacitor protects the rectifier from high voltages. The capacitor also suppresses radio noise sources.
The voltage regulator is a solid-state electronic switch that controls the alternator output. The voltage regulator limits the alternator voltage to a preset value by controlling the field current. The voltage regulator feels the voltage in the system. The voltage regulator switches ON and OFF many times per second in order to control the field current for the alternator. The alternator uses the field current in order to generate the required voltage output.
Note: Refer to Service Manual, SENR3862 for detailed service information for the Delco Remy 21 SI Series Alternator.
Note: If the alternator is connected to an engine component, the ground strap must connect that engine component to the frame or to the battery ground.
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.
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| Illustration 2 | 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
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| Illustration 3 | g00292330 |
Starter motor cross section (1) Field windings (2) Solenoid (3) Clutch (4) Starter pinion (5) Commutator (6) Brush assembly (7) Armature | |
The starter motor rotates the engine flywheel at a rate that is fast enough to start the engine.
The starter motor has a solenoid (2). When the start switch is activated, the solenoid will move starter pinion (4) in order to engage the starter 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 starter 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.
Other Components
Circuit Breaker
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| Illustration 4 | g00281837 |
Circuit breaker schematic (1) Reset button (2) Disc in open position (3) Contacts (4) Disc (5) Battery circuit terminals | |
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.
Magnetic Pickup
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| Illustration 5 | g00285114 |
Schematic of magnetic pickup (1) Magnetic lines of force (2) Wire coils (3) Gap (4) Pole piece (5) Flywheel ring gear | |
The magnetic pickup is a permanent magnet generator with a single pole. The magnetic pickup is made of wire coils (2). The coils go around a permanent magnet pole piece (4) .
As the teeth of the flywheel ring gear (5) cut through the magnetic lines of force (1) around the pickup, an AC voltage is generated. The frequency of this voltage is directly proportional to engine speed.
Magnetic Switch
A magnetic switch is used for the starter solenoid circuit. The switch electrically operates in the same manner as the solenoid. The magnetic switch has the function of reducing the low current load that is on the start switch. The switch also controls the low current to the starting solenoid.
A magnetic switch is used for the air inlet heater circuit. The magnetic switch controls the current to the heater element.