Quote:
Originally Posted by reyn911
A quick update,
With the car running it still is not charging the battery. I suspect the culprit is the resistor per the Tech Bulletin. Can someone explain in plain language how a light inhibits the alternator from charging the battery, how the resistor will fix that issue, and how to wire it in? I have attached images of the part I ordered Per the Tech Bulletin as well as a picture of the back of the gague.
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Question: Is the GEN light on always?
See the diagram for the 914 charging system. The 911 system is very similar. Alternators are pretty simple. Generally if you spin a magnet close to some windings a voltage is induced in the windings.
Alternators use an electromagnet in the armature which spins with the motor and generates ac voltages in the stator windings. The voltage regulator adjusts the current in the armature which adjusts the output voltage. Alternators use a second set of diodes (left side) to create a voltage independent of the battery and vehicle electrical loads (right side) for better stability.
If you remove the GEN light, notice there's nothing to power the VR when the engine is started and the alternator will not generate any voltage. With the GEN light in place, when starting the car, the GEN light will light and basically provide just enough current to get the power the electromagnet in the armature so the alternator can start up. Then the second set of diodes (left side) powers the VR; the GEN light goes out and the alternator runs ok. This is called bootstrapping as the alternator uses its own voltage to start up.
After reading that bulletin, it looks like the OEM 2W GEN light doesn't provide enough current to start the new alternator. They talk about needing a 4W GEN light or add a parallel resistor to the 2W GEN light to provide sufficient current to start the alternator.
