XJ6 & XJ12 Series I, II & III 1968-1992

XJ6 Alternator Problem

 
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Old 12-19-2018, 04:27 PM
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Default XJ6 Alternator Problem

I have issue with the charging system on my 1982 XJ6. After starting when car has sat for a few days, the Batt light on the dash stays on for a minute or so. Then it goes out and all is well. Meter shows 13 volts. What’s weird is that as the light is going out, the engine starts to die for a half second, and then continues to run normally as it did before the light goes out.
This has not been a problem but after sitting for a couple weeks, the battery was dead. I am thinking the alternator exciter circuit was going bad. Is that possible, and what actually is the exciter circuit and what does it do.
Before I pull and replace the alternator, could the problem be elsewhere, say in the dash where the battery bulb is?

Finally if yes on the alternator replace, any advice on removing it besides the sway bar removal.
 
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Old 12-19-2018, 05:16 PM
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well if the car is sitting, and the battery is not being maintained, the fuel system becomes lazy too. You need to exercise it. Drive it every Sunday for at least 1 hour.
That's all it needs. Once the engine starts, and the battery warning light stays ON, rev the engine lightly and you'll see it go out.

buy a battery maintainer at Walmart fot $15. and keep the battery fully charged. These cars like a lot of juice when waking up.
 
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Old 12-19-2018, 09:01 PM
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Originally Posted by Saemetric View Post
I have issue with the charging system on my 1982 XJ6. After starting when car has sat for a few days, the Batt light on the dash stays on for a minute or so. Then it goes out and all is well. Meter shows 13 volts.


OK, at least the system IS charging...although closer to 14v would be better.

What’s weird is that as the light is going out, the engine starts to die for a half second,

That's a little weird, yes. I can't think of a good reason, off hand.

Fortunately there's nothing exotic about your charging system....so all basics apply and are usually sufficient.

If the battery is 100% ...gotta be sure about that....then check all relevant connections at battery posts, ground at fender well, underbody ground straps, and "+" posts on the firewall...and of course at the alternator itself.

The main output wire from the alternator to the firewall can develop excessive resistance causing weird problems.

The wire at the back of the alternator is fragile. Check it.

For giggles, gently giggle the wires at the rear of the ignition switch. Any reaction from the engine or alternator light?

If the battery is good and the wires/connectors are good, there nothing left but the alternator.

Cheers
DD



 
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Old 12-20-2018, 08:33 AM
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Will try all the above. What does the exciter circuit and how does it work.
 
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Old 12-20-2018, 05:39 PM
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3 wire alternator:

In layman's terms, the exciter circuit is a 12 volt circuit connected directly to the battery, starter solenoid or the ignition switch "run" terminal. The wire must carry 12 volts at all times, and is used to trigger the internal voltage regulator. No exciter circuit = no charge. The wire is connected to the voltage regulator on one side of the diode. It is one of the wires on the 2 terminal connector plug on the alternator. When the alternator starts to charge, the diode prevents the 12 volts from going to the battery light so it turns off.
 

Last edited by sanchez; 12-20-2018 at 05:43 PM.
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Old 12-21-2018, 08:30 AM
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Thanks for the explanation, just wish I studied Electrical Engineering instead of Aerospace Engineering. Still wondering why, when the battery light is going out, the engine momentarily starts to die.
 
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Old 12-21-2018, 11:47 AM
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Sanchez:

I appreciate your description of the exciter circuit. Clearest one I've ever read. Am I off base inthat the alternator can perform sans the circuit. At start up, a blip of throttle energizes the alternator. The principle used in the "one wire alternators.

In the case at hand, establishing good wire and good connections will make it work as intended...

I might add that makig the meter do more is easy and so informative. Id made a patch cords. I can connect my meter to the car via the cigar lighter outlet. Volts in real time at various loads and RPM's. The fascia volt meter is incline to be sluggish..

Carl
 
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Old 12-21-2018, 04:08 PM
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Quote from another source: Scott Bower (Painless Wiring)
"A 1-wire alternator has a self-exciting regulator, and doesn’t require a wire running to the regulator to create a turn-on circuit with the ignition. The other two ports that are on the regulator are not needed. When you think of a regular GM alternator with a built-in regulator, most people call it a 3-wire alternator, but really there’s only two wires. There’s the main charge wire, the exciter wire, and a third wire that can jump between the regulator and the battery stud. You still see a third wire, but as far as wiring for the rest of the vehicle, you really only have two wires,”
"Because the 1-wire alternator is self-exciting, it requires the driver of the car to exceed an engine RPM threshold to tell the alternator to start charging. When you pair this requirement with a slow-speed cruise,or a modern fuel-injection setup that controls startup parameters, you can run into trouble meeting the electrical demands of the car".
Me:
In the case of the 3 wire alternator, if the exciter circuit or the internal regulator is faulty, the alternator will NOT charge.
 

Last edited by sanchez; 12-21-2018 at 04:09 PM. Reason: add info
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Old 12-21-2018, 06:32 PM
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FWIW - the gauge in my car reads 13V but the alternator is putting out 14V to the battery. I have a volt meter that plugs into the lighter, verified with a VOM on the battery.

My alternator was slow to wake up when I started the car and would start producing voltage a mile down the road in the mornings. There was no alternator light (or now that I think about it, no other lights on the center annuciator between the tach and the speedo either) The connector was loose. Plugged it in and all was well with the charging system.

Evidently, no light in circuit = no charge. like Sanchez says
 
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Old 12-22-2018, 11:26 AM
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Thanks guys. I continue to learn. And reinforces a term. electrickery.. I did not coin the word. I did adopt it readily and use it.

In the case at hand, it seems that in addition to clean tighten and lube the connections, a removal and cleaning of the alternator might be needed. I suspect internal corrosion or even 'calcified" lube.

Just barely if at all, relevant was a past experience. Circa 1958, my T speedster's generator would stop providing amps to the ammeter. Fix; Remove the cover and expose the armature. Rub the bars with a cloth moistened in gasoline and the amps returned!! Goop or corrosion sensitive...

Carl . ,
 
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Old 12-22-2018, 11:29 AM
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PS!!!

I've an epiphany.

The alternator is fine, The fascia "guage" is slow to awaken !!


Carlm
 
 
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