The electrical system has three separate circuits.
- Charging circuit
- Starting circuit
- 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.
- Battery
- Circuit breaker
- Ammeter
- Cables
- 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.
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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. |
The alternator is a brushless, heavy-duty integral charging system. The alternator has a built-in diode rectifier and a voltage regulator. The system produces DC current for electrical systems.
The solid state integrated circuit voltage regulator that is built into the alternator limits the system voltage by switching the ground circuit for the field coil on and off. This is done rapidly in order to control the current that is in the field coil. Nominal regulated voltages of 13.5 to 14.5 V are available for 12 V systems. The nominal regulated voltage for the 24 V system is between 27 and 29 V.
After the engine is started and rpm rises, the excitation circuit is turned on all the time, and generated voltage rises rapidly. If the "I" terminal is not used, the initial field voltages at start-up are generated by residual magnetism. The residual magnetism can be lost. This results in no output. Loss of the residual magnetism can be caused by extended downtime or a severe shock to the alternator. As the speed increases and the output increases, the voltage that is available at the diode trio becomes sufficient to supply field current for normal operation. When the voltage at the "B" terminal exceeds the battery voltage current flows into the battery.
The 34SI model has an "I" terminal. The terminal CAN be used in order to supply excitation current. The current flows from a source that has a keyswitch through an indicator light. The indicator light provides a verification for alternator excitation and the light also provides an indication of faults. The "I" terminal must have an indicator or a resistor in series between the current source and the "I" terminal. This maintains the normal field current around 0.17 amperes. Once the alternator begins charging, the field current is supplied from the diode trio. Current stops flowing through the "I" terminal and the indicator lamp turns OFF.
The voltage regulator cycles the field current ON and OFF. This cycle occurs many times per second. This maintains the alternator output voltage at a preset level.
For 12 V systems, an output rating of 105 to 110 amperes is standard. For 24 volt systems, output ratings of 60 to 100 amperes are available. Refer to Specification for the output ratings of the alternator.
The output of the alternator must be connected to the positive terminal of the battery through the charging circuit for the machine. A ground path is also required. The ground path should run between the alternator ground terminal and the ground terminal for the battery.
While the system voltage is below the setting of the voltage regulator, the regulator turns ON the field current. This allows the alternator to produce the maximum output. When the voltage setting is reached, the regulator turns OFF the field current. When the field current is off, the magnetic field in the rotor collapses and the alternator output voltage begins to fall. The falling voltage causes the regulator to turn on the field current and the current rebuilds the magnetic field. This cycle continues rapidly. The cycle keeps the output and the system voltage very close to the voltage setting. The cycle will continue unless the electrical demands of the system cause the system voltage to fall below the voltage setting. If the system voltage falls below the voltage setting, the regulator will allow full field current to flow so that the alternator's maximum output is realized. Maximum output is dependent on the alternator speed. At low speeds, the maximum output of the alternator is significantly reduced.
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| Illustration 1 | g00360155 |
The voltage regulator is located inside the alternator. The voltage regulator limits the voltage that is produced by the alternator at the output terminal. This is done by controlling the magnetic field that is present in the stationary field coil. The regulator allows current to flow. The current satisfies the electrical loads that are placed on the electrical system and the current charges the batteries.
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 |
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Typical solenoid schematic | |
The solenoid has windings (one set or two sets) around a hollow housing. A spring loaded plunger assembly is inside of the solenoid housing. The spring loaded 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 spring loaded plunger forward in the housing. 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 spring loaded 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.
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| Illustration 3 | g00292330 |
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Starter motor cross section (1) Field (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 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.
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.
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| Illustration 4 | g00281837 |
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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.