STARTING MOTOR GP-ELECTRIC 1939186 - Caterpillar

Brush Type Alternator
Illustration 2 g00698978
Brush Type Alternator (Typical Example) (1) Stator (2) Field coil (rotor) (3) RegulatorThis alternator design has a stator (1) that is stationary and a field coil (rotor) (2) that moves. The slip rings and the brushes are used for supplying excitation current to the rotating field coil.The brush type alternators can be a battery energized alternator or a self-energizing alternator. The self-energizing alternators rely on residual magnetism, which is similar to the brushless alternators. The battery energized alternators have less residual magnetism. These alternators use current from the batteries for field current in order to produce the magnetic lines of force. When the alternator's voltage exceeds the battery voltage, the charging system will be self-contained and the battery voltage will not be needed.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 3 g00292316
Typical solenoid schematicThe 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