Alternator problem

[DaveShreiner CLC#23834]

My 1984 Eldorado's alternator stopped working and left me with a dead battery.  I replaced it with a remanufactured (not rebuilt) one and found it worked for about 10-15 minutes before it decided to quit.  After letting the car sit for a few hours, it worked again for about the same length of time.  I tried another remanufactured alternator and got the same result.  It seems like something is cutting out or grounding after things heat up.  But what could it be?  Everything checks out with the electrical tests outlined in the 1980 factory manual.  I don't know what to do next.  Is it possible I have got 2 bad alternators in a row?  Other people say that is very unlikely.  Are there diodes somewhere in the circuit outside the alternator?  The wiring diagram gives a negative answer.  The regulator within the alternator is designed to cut out if some connection is grounded but that isn't the case as far as I can tell.

I would appreciate any suggestions.

Dave S.

[Dave Shepherd]

Have you performed the output test as outlined when the alt stops charging, this by-passes the regulator to put the alt in full charge.

[DaveShreiner CLC#23834]

Thanks for replying.  I don't think I know what the "output" test is.  I have measured voltage at the 3 wires connected with the generator.  Voltage drops to 12.2 at the alternator output when the meter on the dash shows battery only.  I did not do the test with the "carbon pile", whatever that is, across the battery.  Is this what bypasses the regulator?

[TJ Hopland]

Did you have the parts stores test the bad alternators?   How about the battery?   Parts and battery stores have the carbon pile / load testers.   Its certainly possible with today's quality to get 2 bad ones but I do wonder if there could be something else going on.     I assume this is not a diesel?     Does one of the wires in the small connector just loop around to the big back terminal?

[Glen]

Back in the early 70s dad lost the generator on his 56 Cadillac.  He went to NAPA and bought a rebuilt and put it on.  It lasted about 5 miles and went bad.  He got another and it lasted about 8 miles.  After going through a few of them I went to the junk and found one on a junked car that looked good.  Dad swapped the brushes out of one of the bad generators and put it on the car.  It lasted until the car was junked several years later. 

It seems the shop doing the rebuild on these did not know you had to wrap the winding tightly or they would fly out as the armature spun. 

So yes the shop that rebuilds them can make the same mistake of many units. 

[bigdave]

I had this same problem on my 84 Eldo and 84 Seville many years ago. Go to the parts store and ask for a self exciting regulator and swap it out with the one in your alternator. Hopefully this will help you out.  Dave

[DaveShreiner CLC#23834]

TJ Hopland,

Yes, this is not a diesel engine.  The parts store tested the alternator in the failed state while in the car and running and it was a failed test.  After removing the alternator, the bench test showed it was good.  This is compatible with how it behaved in the car, i.e., it works for a time then fails, only to work again after letting the car rest.  The battery tested OK.  Yes, one of the wires in the back connector loops around to the battery terminal.

Dave

[DaveShreiner CLC#23834]

BigDave,

Thanks for telling me about your experience.  I had to read about the self-exciting regulators because that was new to me.  It does sound like would solve the problem.  Thanks again.

[Dave Shepherd]

There is no reason to got to any extremes to diagnose or repair this issue, check this link for the how to on bypassing the regulator to check for actual output capabilty of the alt. http://www.ehow.com/how_5220979_troubleshoot-auto-voltage-regulator.html

[TJ Hopland]

The reason I was asking about diesel is they used 2 batteries in parallel and you can get all sorts of odd things going on with that sort of setup.  Since that is not the case here we don't have to explore all those possibilities.

I have an 83 manual around here somewhere, maybe that will be closer than an 80 manual.  Since its snowing today and nothing is good on TV I will go look for it and see if there is anything unusual about the whole charging circuit that year.   Ya never know sometimes they were trying new things.  Sounds fairly typical though.  The fact that the GEN light comes on would seem to imply that the circuit to the alternator is complete.  One side of the light gets + power from one of the dash circuits.  The other side is that small wire in the 2 pin plug.  When the alternator is working you get + from the dash and + from the alternator so the light does not light.  If the alternator is not working the light gets a ground signal from the alternator which then lights the bulb.   The + through the bulb is also what tells the alternator to turn on. 

["Cadillac Kid" Greg Surfas 15364]

Dave,
Check the 2-wire plug for bad connectors and possible loose connections.  Also be sure your power wire to the battery is good through the joint in it.  Those two things will give you all indications of a bad alternator.
Greg Surfas

[TJ Hopland]

I cant find my 83 book but Greg is got good points.  The battery cable is a common place to have an issue.  You get gas leakage from the battery into the connector and it corrodes under the plastic boot. 

[DaveShreiner CLC#23834]

Thanks for all your help.  I have checked the connections and they are OK.  Based on what bigdave said, I think I will try the self-exciting regulator.  I see that alternators can be had with this type of regulator already installed.  Since I am having trouble with the 3-wire alternator I have bought, twice over, I may be able to exchange it at the store for one that is a one-wire alternator, which is another name for the alternator with a self-exciting regulator (because only the wire to the battery is needed for its function).  If anyone thinks this might be a problem because the ignition key will not be used to turn on the alternator and the indicator light in the dash won't work (it doesn't work anyway until conditions are too far gone), I would like to hear about it.  I intend to use a voltmeter to substitute for the indicator light (aka idiot light).

Dave

[76eldo]

Unless you have received two bad alternators, you have another problem.
Check your battery for a dead or shorted cells.

Also check the wires at the starter and the junction point on the fenderwell.

Brian

[TJ Hopland]

I don't think I would put a one wire in. 

How did the parts store do the in car test?   

[DaveShreiner CLC#23834]

76eldo,

That is a good suggestion because the ignition is part of the circuit in this car.

TJ Hopland,

Why do you think a one-wire alternator would not be a good idea?
The parts store used a complex instrument that included a circuit detector, voltmeter, battery test, load and no load conditions.  The no load condition was OK, but the loaded state dropped voltage to 11.4 and a negative 40 amp. draw.

--Dave

[TJ Hopland]

I dont really have a good reason to not do the single wire.  I just don't like em.  Thats what was in my boat and tractor and I always seemed to be having electrical issues with those that I just attributed to inconsistent use.    Both rigs had the alternators get weak and because I was too cheap to get the proper replacements and one wires are extremely rare in the junkyards I replaced both of them with 3 wire ones off junk cars.   Since then I have not had any issues with either rig, not even had to replace a battery in years.   I can't prove that the alternators had anything to do with it and both rigs have minimal electrical stuff on them so other than charging the starting battery they don't have to work that hard.  They are also both summer use only so they dont have to deal with cold starts or constant electrical loads. 

I will have to do some research on what that fancy on car tester was.  Never seen anything like that. 

What does the starter circuit have to do with the alternator?   Its been a while since I have tinkered with a gas car from that era, my only current one is a diesel and the electrical layout is a little different on those. 

[76eldo]

The large positive post on the starter is a major junction point for all of the car's wiring.  The battery wire (obviously), ignition wiring, accessory wiring a lot of it jumps off from there.  Also there is a positive post on the r/s fenderwell.

I have hear of generators needing to be polarized, but never anything like this with a modern alternator with internal regulator.

There are deeper problems with n this car.

Brian

[bigdave]

I have dealt with this problem on more than one occassion on this year and model and the self exciting regulator has solved it everytime. I had no problem with battery lights coming on or ignition system problems. If this car is a low mileage pristine museum quality beauty then maybe tracing wires and other procedures may be warranted. If this is a nice or even really nice driver condition car then the self exciting regulator is the way to go. Dave

[DaveShreiner CLC#23834]

Thanks bigdave.  My 84 Eldo is a very nice driver, not a show car.  I have one question.  When you changed to a self-exciting regulator, were you able to plug the 2-wire plug in, or did you just let it dangle?