Jaguar E-Type Alternator System Explained (page 2)

    It looks complicated, but it's really quite simple. First, note that the ignition switch is connected to the positive side of the battery. When the switch is turned on, power flows to two places: the 6RA alternator relay (located behind the left mudguard, behind the battery), and the 3AW relay (located under the heater air box) via the dashboard indicator light. Here's what each of these components does:

    The 6RA is a simple relay which, when powered by the ignition switch,  connects the alternator field coil and the the 4TR voltage regulator "+" terminal to the battery. The voltage regulator initially sees only the 12 volts coming from the battery. Since it's designed to keep the voltage at 14.3 volts, it immediately connects the F- lead of the alternator to ground in an attempt to increase power output. The field coil in the alternator is now magnetized, ready to produce power.

    The 3AW relay operates the indicator light in the dashboard. Until the alternator is producing power, it's "WL" lead is grounded via it's "E" lead. This allows the dashboard lamp to light.

    To review, at the moment the ignition switch is turned on, the alternator field coil and voltage regulator are powered via the 6RA relay. The voltage regulator immediately grounds the alternator "F-" lead, attempting to increase system voltage. Meanwhile, the 3AW relay completes the indicator light circuit.

    Now start the engine. The rotor begins turning, inducing current in the stator coils. The alternator begins putting out current. Two things happen. First, the voltage at the AL lead on the alternator will rise to about 7.5 volts AC. This will cause the 3AW to disconnect the ground on the indicator light, which goes out. The second thing that will happen is that the voltage at the B+ lead of the alternator will begin to rise. With no intervention, it would rise indefinitely. But the voltage regulator will sense when the voltage rises to 14.3 Volts, and begin turning the rotor coil off and on to keep things under control.

That's it. The whole story. If you've followed the discussion you now know enough to do some serious trouble shooting. Click here to proceed to the trouble shooting section.

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