Charging System: Description and Operation
OVERVIEWThe battery, starting, and charging systems operate with one another, and must be tested as a complete system. In order for the vehicle to start and charge properly, all of the components involved in these systems must perform within specifications.
However, when attempting to diagnose any of these systems, it is important that you keep their interdependency in mind.
The diagnostic procedures used include the most basic conventional diagnostic methods to the more sophisticated On-Board Diagnostics (OBD) built into the Powertrain Control Module (PCM). Use of a induction milliampere ammeter, volt/ ohmmeter, battery charger, carbon pile rheostat (load tester), and 12-Volt test lamp may be required.
All OBD-sensed systems are monitored by the PCM. Each monitored circuit is assigned a Diagnostic Trouble Code (DTC). The PCM will store a DTC in electronic memory for any failure it detects. See the On-Board Diagnostics Test in Starting and Charging/Charging System for more information.
SYSTEM OPERATION
The charging system consists of:
- Generator
- Electronic Voltage Regulator (EVR) circuitry within the Powertrain Control Module (PCM)
- Ignition switch (refer to Powertrain Management/Ignition Switch for information)
- Battery (refer to Starting and Charging/Battery for information)
- Battery temperature sensor
- Generator Lamp (if equipped)
- Check Gauges Lamp (if equipped)
- Voltmeter (refer to Instrument Panel, Gauges and Warning Indicators/Instrument Panel/Voltmeter for more information)
- Wiring harness and connections.
The charging system is turned on and off with the ignition switch. When the ignition switch is turned to the ON position, battery voltage from the powertrain control module (PCM) is supplied to the generator rotor to produce a magnetic field. This is done through one of the two field terminals at the rear of generator. On Jeep models of previous years, battery voltage to this field terminal was supplied from the ASD relay.
The amount of DC current produced by the generator is controlled by the EVR (field control) circuitry contained within the PCM. This circuitry is connected in series with the second rotor field terminal and ground.
A battery temperature sensor, located in the battery tray housing is used to sense battery temperature the battery charging rate. This is done by cycling the ground path to control the strength of the rotor magnetic field. The PCM then compensates and regulates generator current output accordingly
All vehicles are equipped with On-Board Diagnostics (OBD). All OBD-sensed systems, including the EVR (field control) circuitry, are monitored by the PCM. Each monitored circuit is assigned a Diagnostic Trouble Code (DTC). The PCM will store a DTC in electronic memory for any failure it detects. Refer to On-Board Diagnostic Test For Charging System for more information.
The Check Gauges lamp monitors the Voltage, Engine Coolant and Engine Oil Pressure gauges. The lamp is located on the instrument panel. If any of the three gauges detects an extreme condition, the lamp will be illuminated. This is done as reminder to check the three gauges. The signal to activate the lamp is sent via the CCD bus circuits. Refer to Instrument Panel Gauges and Warning Indicator/Instrument Panel/Check Gauge Lamp for additional information.
Generator
The generator is belt-driven by the engine using a serpentine type drive belt. It is serviced only as a complete assembly. If the generator fails for any reason, the entire assembly must be replaced.
As the energized rotor begins to rotate within the generator, the spinning magnetic field induces a current into the windings of the stator coil. Once the generator begins producing sufficient current, it also provides the current needed to energize the rotor.
The Y type stator winding connections deliver the induced AC current to 3 positive and 3 negative diodes for rectification. From the diodes, rectified DC current is delivered to the vehicle electrical system through the generator battery and ground terminals.
Although the generators appear the same externally, different generators with different output ratings are used on this vehicle. This will depend upon engine size and optional equipment. Be certain that the replacement generator has the same output rating as the original unit. See Generator Ratings in the Specifications for amperage ratings.
Noise emitting from the generator may be caused by: worn, loose or defective bearings; a loose or defective drive pulley; incorrect, worn, damaged or misadjusted fan drive belt; loose mounting bolts; a misaligned drive pulley or a defective stator or diode.
Battery Temperature Sensor
The battery temperature sensor is used to determine the battery temperature and control battery charging rate. This temperature data, along with data from monitored line voltage, is used by the PCM to vary the battery charging rate. System voltage will be higher at colder temperatures and is gradually reduced at warmer temperatures.
Battery Temperature Sensor Location:
The sensor is located under the vehicle battery, and is attached to the battery tray.
Voltage Regulator
The Electronic Voltage Regulator (EVR) is not a separate component. It is actually a voltage regulating circuit located within the Powertrain Control Module (PCM). The EVR is not serviced separately If replacement is necessary, the PCM must be replaced.
Operation: The amount of DC current produced by the generator is controlled by EVR circuitry contained within the PCM. This circuitry is connected in series with the generators second rotor field terminal and its ground.
Voltage is regulated by cycling the ground path to control the strength of the rotor magnetic field. The EVR circuitry monitors system line voltage and battery temperature (refer to Starting and Charging/Battery/Battery Temperature Sensor for more information). It then compensates and regulates generator current output accordingly Also see Charging System Operation for additional information.
CIRCUIT OPERATION
The charging system is an integral part of the battery and starting systems. Because all these systems work in conjunction, diagnose and test them together.
Circuit A11 connects to the generator output terminal and splices to the Power Distribution Center (PDC). Circuit A0 connects the battery to the PDC. Circuit Z0 provides ground for the generator.
When the ignition switch is in either the START or RUN positions, it connects circuit A1 from fuse 3 in the PDC to circuit A21. Circuit A21 feeds circuit F12 through fuse 11 in the fuse block. Circuit F12 splices to supply current to the coil side of the Automatic Shut Down (ASD) relay. The Powertrain Control Module (PCM) provides ground for the relay on circuit K51. Circuit K51 connects to cavity C3 of the PCM.
When the PCM grounds the ASD relay, contacts inside the relay close and connect circuit A14 from fuse 6 in the PDC to circuit A142. Circuit A142 splices to supply system voltage to cavity C12 of the PCM. Circuit K72 from cavity C25 of the PCM supplies current to the generator field terminal.
The PCM has an internal voltage regulator that controls generator output. The PCM controls the generator field on circuit K20. Circuit K20 connects to PCM cavity B10.
When the engine operates and there is current in the generator field, the generator produces a B+ voltage. The generator supplies B+ voltage to the battery through the A11 and A0 circuits.