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I read somewhere recently that an led alternator charge light will not excite the alternator enough and it should be left as a std bulb. Anyone found this to be the case?
No experience; can't say. It is plausible that the LED could cause a problem.
However.....
As seen in the diagram Jaguar installed a resistor in the warning light circuit. I have always presumed that the idea was to provide enough resistance to excite the alternator in event of a bulb failure.
The warning light shouldn't have to do with exciting the alternator.
Any alternator will self excite once is reaches about ~6000 alternator RPM.
The resistor in parallel with the warning light just keeps the light from coming on if the alternator is putting out juice. Now whether an LED light will come on or not, vs a regular bulb, i have no idea.
A typical three wire alt has the power wire, the wire to the light/resistor,and a wire to a reference voltage source.
The so called one wire alternator is just an alternator with only one wire hooked up, thats why the don't excite until higher motor RPM (~2000 motor RPM, or so).
The warning light shouldn't have to do with exciting the alternator.
Any alternator will self excite once is reaches about ~6000 alternator RPM.
But "bootstrap" current through the bulb excites the alternator almost instantly. I've never really understood what bootstrap current is but, anyhow, this arrangement is virtually standard fare on all old-ish cars. I suspect a better way was devised some time ago for new-ish cars.
Just Google "alternator exciter bulb" for a good explanation
The resistor in parallel will also allow the alternator to excite when the key is on, you just need voltage at that alternator terminal.
The resistor allows excitement even if the bulb is burned out, which is why the resistor is there, the resistor also will allow the bulb to light if the alt fails..
Led warning lights
