0378883 JOHNSON HOUSING, Starter

Charging System Components
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
Illustration 1 g03071036
(1) "B+" Output terminal
(2) "B-" Ground terminal
(3) "R*" AC tap for stator
(4) "D+" Terminal Note: * The "R" terminal may be used to calculate frequency: Frequency = Speed (rpm) / 7.5.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.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.If the alternator has an "I" terminal, this 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 a resistor in series between the current source and the "I" terminal. The resistor maintains the normal field current around 0.17 A. 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 cycling maintains the alternator output voltage at a preset level.For 12 V systems, an output rating of 105 A to 110 A is standard. For 24 V systems, output ratings of 60 A to 105 A are available. Refer to the correct "Specifications Manual" 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.When the system voltage falls below the setting of the voltage regulator, the regulator turns on the field current allowing 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 maximum alternator output is realized. Maximum output is dependent on the alternator speed. At low speeds, the maximum output of the alternator is reduced.Regulator
Illustration 2 g00360155The voltage regulator is located inside the alternator. The voltage regulator limits the voltage that is produced by the alternator at the output terminal. The alternator limits the voltage 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.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 switching is done rapidly in order to control the current that is in the field coil. Nominal regulated voltages of 13.5 V to 14.5 V are available for 12 V systems. The nominal regulated voltage for the 24 V system is between 27 V and 29 V.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 3 g00292316
Typical solenoid schematic
The solenoid has windings, one of 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 movement causes the shift lever to mesh the gears of the pinion drive gear with the gears of 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 number 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