Alternator problems?

[old_skul]

Last night, after welding my exhaust back together, I took my car for a test drive. It took a couple of extra cranks to get it started. I left it sitting for a few minutes waiting on a friend, running.

We drove off, and it being nighttime out, I had my lights on. I noticed my lights were dim, and my instrument lights were dim. Halfway around the block I pulled up next to my friend, who advised killing the engine and we'd see what happened. I did, and it wouldn't start again - dead battery. We bump started it and went back to the garage.

After a couple of hours on a battery charger, it started normally. I drove home with no radio and only headlights. This morning, it started normally.

What does it mean when the battery light does NOT come on with the key in the Run position? This happens intermittently. When I started the car this morning it came on, but after driving to work, it does not come on when I go to start the car.

Is my alternator dead?

[RoninLB]

no lite = no charge

[MotoSook]

The guys I work with who have been around electrical equipment and welding, make sure that the electrical equipment is "floating" when welding so that any potential to arc inside the electrical equipment is minimized.

Next time you weld on your car, disconnect the ground from the battery..don't know if it is an issue on cars, but better safe than sorry.

I'm not saying that happened in your case, but it sure is suspicious. Put a multimeter on your battery and have someone rev the motor. You should get over 13 VDC if the ALT is healthy. (You can also check the voltage at the rear relay panel and rev the motor yourself.)

If the ALT or VR are intermittent, the meter test may not should anything if the timing is right, so try to catch the bastard when the lights start to go dim..most likely when the car has warmed up (just a guess).

[old_skul]

Rrrr. Great, that means I'm stuck here.

[old_skul]

Originally posted by Souk
Next time you weld on your car, disconnect the ground from the battery..don't know if it is an issue on cars, but better safe than sorry.

The exhaust was off the car. Not a factor. Good guess, though.

[304065]

Mark, the question is, what is the light telling you? Key to run position, battery light should come on before you start the engine. Once you start, the light should go out as soon as you rev the engine above what Warren calls "Zero-Ampere Speed" which is around 800 rpm in my car. Current flows from the battery through the warning light and back to the D+/61 terminal on the alternator, then into the alternator field and to ground. This current flow generates a magnetic field in the alternator, which induces a current in the stator windings, which flows through the diodes and into the "trio" which then engerizes the field itself-- "bootstrapping" the alternator. At that point, the voltage flowing through the field is 12v or higher, and there is no longer a potential difference between the battery positive terminal and the alternator field, so the light on the gauge goes out.

So if the light on the gauge doesn't light when the engine is off, that means one of two things: either your battery is so discharged that the voltage is insufficient to light up the bulb, or you have a loose connection somewhere along the D+/61 "Blue Wire" circuit. Check the connections at the rear of the bulb holder- you should have a switched +12v red with black stripe going in, and a blue wire out, then check the 14-pin connectors on the electrical console in the engine compartment. If you ground pin #11 of the rear 14-pin connector, the light should come on. If it doesn't, there's your problem. You could also have a burned-out bulb, which will keep the system from charging.

I would say that bad diodes in the alternator or a bad VR are the last thing you should worry about-- they don't tend to go unless subjected to heat or abuse e.g. disconnecting the battery with the engine running.

Good luck!

[old_skul]

I don't think the bulb is burned out, since it came on this morning. My oil light comes on when the key is moved. Does this mean there's not enough juice for that specific circuit, or does that indicate that perhaps there's a loose connection somewhere?

[targa80]

I would suspect a loose connection or a dirty connection since the light sometimes comes on in the run position. You should check all of the connections in the circuit and also pull the bulb and make sure that it is seated in the connector all the way.

[old_skul]

I'm really, really certain that the bulb is okay, since it lit this morning, but not last night when the battery was dead. After charging the battery it was fine.

My mechanic Ken Farler says alternator, alternator, alternator. I'm going to drop it off with him today.

[MotoSook]

If you think it is your alt, check with a v-meter while the car is running, rev to verify high rpm voltage.