Question about Dodge Ram 3500

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I have a Dodge 3500 van with a 5.2 engine. The battery was discharged which led me to believe the alternator was not charging. I put a voltmeter on the batttery, and there was no charge. Therefore, I replaced the alternator with a new one, and the alternator does not charge.. Could it have a defective voltmeter?

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  • Ursulo Robles Oct 01, 2010

    thanks for the info



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Are you sure that there is battery power to the new alternator?

If the answer is ' yes ', this seems to be a bad news for you.On most occasions, it is bad ECM.

Make sure that the connector is fine.

How it plays a role in alternator is explained below :-

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. (not uncommon on these cars)

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 . It then compensates and regulates generator current output accordingly.

The battery, starting, and charging systems operate with one another, and must be tested as a complete system. To allow the vehicle to start and charge properly, all of the components involved in these three systems must perform within specifications.

When attempting to diagnose any of these systems, it is important to keep their interdependency in mind.

Certain charging system circuits are monitored by On-Board Diagnostics (OBD) built into the Powertrain Control Module (PCM) . Each monitored circuit is assigned a Diagnostic Trouble Code (DTC) . The PCM will store a DTC in electronic memory for certain failures it detects. For charging system diagnostic information, refer to the appropriate Powertrain Diagnostic Procedures.

The charging system consists of:

  • Generator
  • Electronic Voltage Regulator (EVR) circuitry within the Powertrain Control Module (PCM)
  • Ignition switch (refer to Powertrain Management/Ignition System 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 and Gauges for 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.

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. This temperature data, along with data from monitored line voltage, is used by the PCM to vary 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 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 certain failures it detects.

The Check Gauges Lamp (if equipped) monitors: charging system voltage, engine coolant temperature and engine oil pressure. If an extreme condition is indicated, 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. The lamp is located on the instrument panel.

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. Be certain that the replacement generator has the same output rating and part number as the original unit. Refer to Generator Ratings in the Specifications for amperage ratings and part numbers.

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.

I would suggest you to take the car to the dealer so that they could exactly diagnose the same before you order something that would cost you few hundred bucks.

Let me know,if needed further assistance.

Hope i helped you.

Thanks for using ' Fixya ' and have a nice day!!

Posted on Oct 01, 2010


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13.85 volts is barely sufficient and would indicate an alternator fault if the reading was taken "off-load"..

An alternator is not designed to charge the battery and is incapable of doing so because the terminal voltage of the battery quickly rises to fool the voltage regulator into believing even a discharged battery is fully charged and will quickly reduce the charge rate to a trickle.

The alternator is therefore designed to keep a fully charged battery fully charged by supplying all the current for the vehicle equipment and the output rating is chosen for this purpose.

The voltage regulator should limit the off-load voltage to about 14.5 volts but that is only a small part of the alternator test. A professional would apply a load across the battery equal to the rated output while monitoring the voltage and current. Most healthy alternators exceed specifications.

For a sensible in-service test when an adjustable load isn't available, with a fully-charged battery it is sufficient to start the engine, leaving it to idle and switch on all the vehicle equipment. Fit a voltmeter to the battery and wait while the battery voltage is pulled down by the load - to around 12.5 volts. Raising the engine speed to 2500/3000 rpm should cause the voltmeter to suddenly rise.
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