2000 Other Jaguar Models Alternator

  • 2000 JAGUAR
  • V8
  • 2WD
  • 79,500 MILES
I recently replaced my alternator with a Bosch AL940X (Bosch's callout for a 2000 jag S-Type 4.0L). I now find I have about a 3 amp load on the battery after the auto is turned off, the key is removed and the electronics have "gone to sleep" (takes about 40 minutes for the car hibernate). The only way to eliminate this draw is to remove a 5 amp fuse in the luggage fuse box (fuse is called "Alternater Sensor).
Can you advise where I can find a diagram of the alternator explaining what this is for and why it would produce a 3 amp load?

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have the same problem?
Tuesday, October 21st, 2008 AT 2:01 PM

1 Reply

The generator is a Nippondenso type L3B-HE that is driven by a single, multi-ribbed belt which also drives all other accessories. The Generator output is 120 amps when generator rotation speed is approximately 5000 RPM at 77 F (25 C).
The generator is belt driven by the accessory drive belt. When the engine is started, the generator begins to generate Alternating Current (AC) which is converted to Direct Current (DC) internally. The DC current is controlled by the voltage regulator, (located on the back of the generator), and then supplied to the battery.
Generators are battery sensed which means that the voltage regulator senses the output voltage at the battery via fuse No. 15 (5A) located in the rear power distribution fuse box. The warning light will illuminate if fuse No. 15 (5A) has failed. When the generator is not generating power with the ignition turned on, a warning indicator will illuminate in the instrument cluster.
The 3.0L V6 generator is solidly mounted to the engine cylinder block and the 4.0L V8 generator is pivot mounted and uses a body mounted cooling duct. The generators are driven at approximately 3 times the engine speed. Generators should be repaired as an assembly and not dismantled for repair.
As with most vehicle AC generators, there is only minimal residual magnetism in the field (rotor) windings. To compensate for this and to achieve high current output at low engine speed, the field is excited by battery voltage supplied to the generator at the IG terminal. To control the level of field excitation and ultimately generator output, the voltage supplied to the field (rotor) is controlled by the voltage regulator. The voltage regulator senses battery terminal voltage at the B terminal (positive main output terminal), which within limits is proportional to the state of charge of the battery. The regulator then adjusts the supplied voltage between the IG terminal and the regulator F terminal (a continuously variable process) to maintain the positive main output (B terminal) at a constant level. If the field were not controlled, the positive main output would rise to a level which could damage bulbs and ECMs. The regulator compares the output voltage to an internal voltage reference circuit to achieve the controlled output of the generator. See Fig. 1.
Fig. 1: Identifying Generator Internal Circuit (Typical)
Courtesy of JAGUAR CARS, INC.
The output from the generator positive main output terminal passes to the battery via the main terminal on the starter motor and then the power cable to the high power protection module located in the luggage compartment. From this module, a short main power cable supplies the battery positive terminal. The return circuit is through the vehicle body and supplementary ground cables. The high power protection module comprises four fuses, each rated at 250 amps. Battery output uses the same power cable as the charging circuit to the high power protection module and to the starter motor main terminal. There are 2 similar cables of lower rating that supply battery power from the high power protection module to the fuse box in the luggage compartment and to the fuse boxes at the front of the vehicle. The interference suppression module (where fitted) connects to the generator positive main output terminal and a ground stud on the rear of the generator. A 3-pin connector is on the rear of the generator supplies ignition voltage to the regulator through terminal No. 2 and output to the charge warning lamp through terminal No. 3. Terminal No. 1 is not used. See Fig. 2.
Fig. 2: Identifying Generator Charging Circuit (Typical)
Courtesy of JAGUAR CARS, INC.
Although the output from the generator is finely controlled and relatively smooth, it is still a pulsed DC output at a varying frequency proportional to engine speed. The suppression module dampens out any ripple which may be sensed on the main output of the generator. This prevents possible interference via the power supply, affecting the radio reception or, where fitted, the telephone. The module is located on the right hand side of the engine compartment adjacent to the generator. It is secured to a mounting bracket by 3 bolts. A fuse is fitted internally to the suppression module to protect the generator output in the event of a short circuit within the suppression module.
The voltage regulator is integral to the generator. The battery charging capability has been optimized for charging a battery which is located remotely, in the luggage compartment. The design of the generator and regulator has been finely matched, to generate charging current with very low ripple. This provides the best electrical refinement to the system.
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Saturday, October 31st, 2009 AT 7:07 AM

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