879172138 Mercruiser VALVE, Pressure

The disconnect switch, if equipped, must be in the ON position in order to let the electrical system function. There will be damage to some of the charging circuit components if the engine is running with the disconnect switch 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 charging circuit is connected through the ammeter. The starting circuit is not connected through the ammeter.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 g00292313
Alternator (1) Regulator (2) Roller bearing (3) Stator winding (4) Ball bearing (5) Rectifier bridge (6) Field winding (7) Rotor assembly (8) FanThe alternator is driven by the crankshaft pulley through a belt. When the engine is running, the pulley rotates the shaft inside the alternator. The rotor assembly is attached to the shaft. The rotor assembly has many magnetic poles. The magnetic poles are similar to fingers. An air space exists between each of the opposite poles. 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 the 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.Regulator
Illustration 2 g00360155
Typical regulator assemblyThe 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
Illustration 3 g00292316
Typical solenoid schematicA 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.Electric Starting Motor
Illustration 4 g00292330
Starter motor cross section (1) Field (2) Solenoid (3) Clutch (4) Starter pinion (5) Commutator (6) Brush assembly (7) ArmatureThe 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, solenoid (2) will move starter pinion (4) in order to engage starter pinion (4) to the ring gear on the engine flywheel. Starter pinion (4) and the ring gear will engage when the circuit between the battery and the starter motor is closed by the electric contacts in solenoid (2). When the circuit between the battery and the starter motor is complete, 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, starter pinion (4) will move away from the ring gear.Other Components