The charging circuit is in operation when the engine is running. The alternator makes electricity for the charging circuit. The voltage regulator in the charging circuit controls the electrical output in order to keep the battery at a full charge.
The starting circuit is in operation only when the start switch is activated.
The low amperage circuit and the charging circuit are connected together on the same side of the ammeter. The starting circuit connects to the opposite side of the ammeter.
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| Illustration 1 | g00333019 |
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Alternator (1) Slip rings (2) Fan (3) Stator (4) Rotor (5) Brush assembly | |
The alternator is a three-phase, self-rectifying charging unit. The alternator is driven from an auxiliary drive by a V-belt.
The alternator has three main parts. Rotor (4) creates magnetic lines of force. Stator (3) produces alternating current (AC). The rectifying diodes change the AC into direct current (DC).
The electrical current for the alternator goes through the brushes. The field current is two to three amperes. The rectifying diodes send current from the alternator to the battery or the load. The rectifying diodes do not move current from the battery to the alternator.
The voltage regulator is a transistorized electronic switch. The voltage regulator controls the voltage output from the alternator. The voltage regulator has two basic circuits, the load circuit and the control circuit.
The load circuit provides the regulator with voltage. The voltage determines the amount of current that is sent to the rotor's windings. The charging voltage is accomplished by cycling the control circuit on and off. The cycles of the control circuit are controlled by the load circuit. This controls the alternator output voltage.
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| Illustration 2 | g00661827 |
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(1) Field (2) Solenoid (3) Clutch (4) Pinion (5) Commutator (6) Brush assembly (7) Armature | |
When the start switch is activated, solenoid (2) moves pinion (4) in order to engage the ring gear on the flywheel. The pinion and the ring gear engage before the circuit between the battery and the starting motor is closed by the electric contacts in the solenoid. When the circuit between the battery and the starting motor is complete, the pinion rotates the flywheel. Clutch (3) provides protection for the starting motor so that the engine cannot turn the starting motor too fast. When the start switch is released, the pinion moves away from the ring gear.
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| Illustration 3 | g00292316 |
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Typical cross section of a 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.
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 starting 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 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 uses a smaller amount of current from the battery and heat that is created by the solenoid is kept at an acceptable level.