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Starting and Charging System

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The first step in understanding a vehicle's starting and charging systems is to learn about basic electricity. For more information on electrical circuits, how they work and how to troubleshoot them, please refer to the information on The electrical system elsewhere in this manual.

The starting system

General information
See Figures 1, 2, 3 and 4

The starting system includes the battery, starter motor, solenoid, ignition switch, and in some cases, a starter relay. An inhibitor (neutral safety) switch is included in the starting system circuit to prevent the vehicle from being started while in gear.

When the ignition key is turned to the start position, current flows and energizes the starter's solenoid coil. The energized coil becomes an electromagnet which pulls the plunger into the coil, the plunger closes a set of contacts which allow high current to reach the starter motor. On models where the solenoid is mounted on the starter, the plunger also serves to push the starter pinion to mesh with the teeth on the flywheel/flexplate.

Figure 1 A typical starting system converts electrical energy into mechanical energy to turn the engine. The components are: battery, to provide electricity to operate the starter; ignition switch, to control the energizing of the starter relay or solenoid; starter relay or solenoid, to make and break the circuit between the battery and starter; starter, to convert electrical energy into mechanical energy to rotate the engine; starter drive gear, to transmit the starter rotation to the engine flywheel.
A typical starting system converts electrical energy into mechanical energy to turn the engine.

To prevent damage to the starter motor when the engine starts, the pinion gear incorporates an over-running (one-way) clutch which is splined to the starter armature shaft. The rotation of the running engine may speed the rotation of the pinion but not the starter motor itself.

The starting of the engine signals the driver to release the ignition key from the start position, stopping the flow of current to the solenoid or relay. The plunger is pulled out of contact with the battery-to-starter cables by a coil spring, and the flow of electricity is interrupted to the starter. This weakens the magnetic fields and the starter ceases its rotation. As the solenoid plunger is released, its movement also pulls the starter drive gear from its engagement with the engine flywheel.

Figure 2 Cut-away view of a typical starter motor equipped with a starter mounted solenoid.
Cut-away view of a typical starter motor equipped with a starter mounted solenoid.

Figure 3 Exploded view of a common starter motor with the solenoid mounted on the motor itself.
Exploded view of a common starter motor.

Figure 4 Exploded view of a typical starter motor from a vehicle which utilizes a separately mounted solenoid.
Exploded view of a typical starter motor.

Some starting systems employ a starter relay in addition to the solenoid. This relay may be located under the instrument panel, in the kick panel or in the fuse/relay center under the hood. This relay is used to reduce the amount of current the starting (ignition) switch must carry.

There may be one other component included in the starting system; on vehicles with automatic transmissions, a neutral safety switch (often referred to by many various names by the different manufacturers, such as: transmission range sensor, neutral safety switch, park/neutral switch, etc.) on the side of the transmission is wired to the relay or solenoid. Its function is to prevent activation of the starter (by creating an open circuit) when the transmission is in any gear other than P (park) or N (neutral). The vehicle can only be started in P or N. Most manual transmission vehicles have a clutch switch to prevent starting the vehicle unless the clutch is depressed.

Troubleshooting basic starting problems

The charging system

General information
See Figures 25 thru 30

A typical charging system contains an alternator (generator), drive belt, battery, voltage regulator and the associated wiring. The charging system, like the starting system is a series circuit with the battery wired in parallel. After the engine is started and running, the alternator takes over as the source of power and the battery then becomes part of the load on the charging system.

Some vehicle manufacturers use the term generator instead of alternator. Many years ago there used to be a difference, now they are one and the same. The alternator, which is driven by the belt, consists of a rotating coil of laminated wire called the rotor. Surrounding the rotor are more coils of laminated wire that remain stationary (which is how we get the term stator) just inside the alternator case. When current is passed through the rotor via the slip rings and brushes, the rotor becomes a rotating magnet with, of course, a magnetic field. When a magnetic field passes through a conductor (the stator), alternating current (A/C) is generated. This A/C current is rectified, turned into direct current (D/C), by the diodes located within the alternator.

Figure 25 Identification of the components utilized in a typical automotive charging system.
Identification of the components utilized in a typical automotive charging system.

Figure 26 Exploded view of a common alternator. Note that the regulator mounts to the rear side of the assembly.
Exploded view of a common alternator-note that the regulator mounts to the rear side of the assembly.

Figure 27 Cut-away view of a common alternator, showing all of the internal components.
Cut-away view of a common alternator, showing all of the internal components.

Figure 28 Common charging system schematic. Note that not all vehicles are equipped with an ammeter in the circuit.
Common charging system schematic-note that not all vehicles are equipped with an ammeter in the circuit.

Figure 29 Negative and positive diodes convert AC current into DC current. Note that the AC current reverses direction while the DC current flows in only one direction.
Negative and positive diodes convert AC current into DC current-note that the AC current reverses direction while the DC current flows in only one direction.

The voltage regulator controls the alternator's field voltage by grounding one end of the field windings very rapidly. The frequency varies according to current demand. The more the field is grounded, the more voltage and current the alternator produces. Voltage is maintained at about 13.5-15 volts. During high engine speeds and low current demands, the regulator will adjust the voltage of the alternator field to lower the alternator output voltage. Conversely, when the vehicle is idling and the current demands may be high, the regulator will increase the field voltage, increasing the output of the alternator. Some vehicles actually turn the alternator off during periods of no load and/or wide open throttle. This was designed to reduce fuel consumption and increase power. Depending on the manufacturer, voltage regulators can be found in different locations, including inside or on the alternator, on the fender or firewall and even inside the PCM.

Figure 30 The alternator converts mechanical energy into electrical energy by using the rotation of the engine's crankshaft as a source of power.
The alternator converts mechanical energy into electrical energy by using the rotation of the engine's crankshaft as a source of power.

Drive belts are often overlooked when diagnosing a charging system failure. Check the belt tension on the alternator pulley and replace/adjust the belt. A loose belt will result in an undercharged battery and a no-start condition. This is especially true in wet weather conditions when the moisture causes the belt to become more slippery.

The warning indicator light or ammeter
See Figures 52 and 53

Frequently a loose or slipping belt is the cause of a glowing or flickering alternator warning light.

Most modern vehicles have an indicator light located on the dash to alert the driver of a malfunction in the charging system. It is also used to pass a small amount of battery current to the alternator rotor to excite and produce the magnetic field until the alternator begins to charge and can assume this function itself.

Because the bulb circuit is connected to the battery and alternator sides, any movement of current between the two units will cause the bulb to light. As the alternator begins to charge and the produced voltage reaches the battery voltage, the current between the two units ceases to move and the bulb will go out. If either the battery or the alternator should fail as the vehicle is being driven, the difference of voltage between the two units will allow current to flow and the bulb to light, warning the driver of a malfunction.

An ammeter also indicates the condition of the charging system. A low battery will be indicated by a high charging current toward (+) side of the gauge. A wiring short or faulty accessory will show as a high rate of discharge toward (-) side of the gauge. It's normal for the gauge to move a slight amount in either direction.

Figure 52 Your vehicle may be equipped with an ammeter gauge, an indicator of charging system condition.
Your vehicle may be equipped with an ammeter gauge, an indicator of charging system condition.

Figure 53 Voltmeters may also be used to indicate battery and charging system status.
Voltmeters may also be used to indicate battery and charging system status.

Troubleshooting basic charging system problems

Starting and charging system maintenance

The only periodic maintenance that can be performed on the starting and charging systems is to inspect the electrical cables and wires for fraying and breakage (refer to the section on "Battery and Cables" in this manual), and to inspect the alternator drive belt for proper tension, wear or damage and replace or adjust the belt as necessary (please refer to the "Cooling System" section for information on drive belts). Follow the maintenance intervals in this section, but make a general visual check each time the hood is opened.

Starting and charging maintenance intervals

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1998 W. G. Nichols - Chilton's Easy Car Care