Charging system light question


Old 11-09-09, 06:52 AM
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Join Date: Oct 2006
Location: Upstate NY
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Charging system light question

A few weeks ago, the alternator gave up the ghost on my 2000 Hyundai Elantra, with well over 230K miles. It was the original alternator, so it's not like it was a big surprise or anything like that. What did surprise me was that the warning light didn't go off, telling me that the alternator was dead. Instead, I ran the battery down so low that the engine would stall when I used the turn signal, and wouldn't even try to crank or jump-start.

Anyhow, a tow and new alternator later, the car runs (aside from a check engine light- see my other post), and the warning light comes on when I first turn the key, then goes out when I start the car. I don't remember if the light ever came on when the alternator was dying. It did not light up when the battery was nearly dead. I traced out the logic for the warning light, and it looks like it is controlled by the voltage regulator on the alternator. If the regulator itself were faulty, would that be a reason as to why the light never came on?
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Old 11-09-09, 09:15 AM
Join Date: Jan 2006
Location: Owen Sound Ontario Canada
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I never looked at wire schematic for your vehicle so I could be wrong but I think the light goes out in responce to Alt output canceling out the battery supply.
That is if there was output of 14.5 volts from the alternator but a live or dead short in the output wire prevented it from going to the Positive post on the battery then the light would not come on and the load would be off the battery until the battery when dead.
If the regulator was bad then little or no field current would go to the field windings and therefore little or no armature current would develop and no voltage and the tell tale lite would come on.
Old 11-11-09, 05:27 AM
Join Date: Jan 2007
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charge light

When you turn the switch on current from the switch flows to the light and grounds at the alt causing the light to light up. When the alt starts charging there is the same voltage on both sides of the light so no current flow and no light. If you had an open circuit in the alt. the light would not come on. Back in "the day" we had some that the light would glow even when everything was OK. we had to solder a resister in the circuit to stop this.
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