SIII Alternator Woes - Anyone Else Seen This?

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I have found that my alternator starts dying as it heats up. First thought is to check the regulator. No problem there. As a matter of fact, as the alternator dies with heat, I can see that the regulator is gradually pulling the negative field closer and closer to ground in an effort to boost the output until finally the field is seeing full current but the alternator output seems to be dying off; that is, the voltage drifts down to be the same as the battery.

I have also done the alternator test as shown in the manual with the regulator disconnected and a short from the field negative to ground. Cold, it passes with flying colors. Hot, it fails miserably.

I could not find any flakey connections when disassembling the alternator. All the diodes check out OK and I have gone so far as to use a light bulb that pulls 2 amps to verify that it isnā€™t a lack of current from my VOM that could be giving me a false reading. I used the same light bulb to check the windings and found no problems. All in all, Iā€™ve had this thing apart and back together again 3 times, each time making sure that the connections are all clean and tight.

With no progress, I have taken it to an alternator rebuild shop that is highly respected around here and they said that they took it apart, did some cleaning and put it back together again and after testing, said it works as it should, under a full 60 amp load. When reiterating the symptoms relating to heat, they said they really donā€™t have any way to test under heated conditions, but insisted that it was working perfectly and that my regulator was probably at fault. After explaining the on car test with the regulator disconnected they really had no answer as to the problem. Iā€™ll be picking it back up tomorrow.

Unless thereā€™s someone out there that might have a clue, Iā€™m considering switching to a Denso alternator, which brings up another question. Does anyone have any experience with the Denso unit as sold by Terryā€™s? As near as I can tell, itā€™s the Denso 210-0410 thatā€™s used in the 91 & 92 Volvo 740 and is rated at 80 amps. The only issue I can see is that it is used in the Volvo rotating Clockwise as opposed to the SIII application where it rotates Counter Clockwise. Is the fan bi-directional in these as it is on the Butec?

There are other vendors out there selling similar Denso alternators as a drop in replacement for the Butec, and in the process eliminating itā€™s regulator, however, I havenā€™t been able to tell which Denso model it is that they are selling.

Suggestions welcome.

PS During all this I have been able to document the newer style Butec regulator. Pics attached.

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Iā€™ve had my ā€˜74 OTS since 1996 and am the 3rd owner. The second owner installed a Leece-Neville alternator as a replacement to the original. I didnā€™t know it until I had to have it rebuilt and the guy at the shop told me that it was a period unit made by Butec/Leece-Neville for heavier duty applications. Itā€™s identical in appearance to the original unit and mounts exactly the same way as the factory alternator. The difference is that it has an internal voltage regulator rather than remotely mounted Butec regulator. Iā€™ve had no problems since it was rewound 20 years ago.

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I wonder if you have taken a look at the VR, that is mounnted on the LHS near the firewall. I have had problems with the rheostat inside this deviceā€¦the rheostat was dirty. Also there were dubious connections on the PCB which i renewedā€¦and last but not least I cleaned the 6 contacts on the wires linking the VR to the Alt.

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EE here, a diode or diodes could be failing and shunting current when it gets hot. If one of them goes open or leaky when they get hot, this might be the problem. When this happens it snowballs because the leakage current generates more heat. When I disassembled and inspected my series 2 alternator, I unsoldered the diodes and checked both their forward voltage drop and reverse standoff voltage, I think I checked them at 50 Volts. The shop could have covered the cooling holes and run it under load for a while to see if there was a problem. If you have access to a scope you can watch the voltage at the alternator and see all the humps from the 3 poles. If a diode is bad then there is a missing or distorted hump. Could also be a winding short that only happens when hot. https://www.circuitspecialists.com/blog/testing-an-alternator-with-an-oscilloscope/

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Donā€™t know where you are located, but if in the USA, send alternator to Quality Remanufacturing in Paterson, NJ 973 523 8800 . They are the best, and most reasonable in the USā€¦do work for all the major shops. Cost should be about $150US. If it has not been done, they will also install a new modern voltage regulator. Simply disconnect the old one. Goof luck !

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Heat and electronics not a good relationship! Heat and an alternator failure? Sounds like expansion and contraction issue in the alternator. Something must be expanding and causing a weak connection to open up and open the circuit. I have had my Butec apart and back quite a few times and canā€™t think of where that might be happening except at the terminal connections. That is where the greatest heat source is. Or the wire connection to the end of the armature shaft.
Hope this might be helpful
Dave L

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Now boysā€¦do you really believe heat is an issue for a healthy alternator ? Absolutely not. I have had my Series 3 for ever, and I believe I might have re-built twice. Once it really needed it (stator) , the other time I foolishly let some crook go ahead and rebuild a perfectly healthy one. Let me leave you with one point to ponderā€¦if heat was a killer for alternators in automobiles, should we not all join forces and get in the alternator overhaul business ?? Happy motoring !

JJ

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Steve, I do not like grasping at long shots, but it appears you have gone over the important items, including bypassing the voltage regulator. The main hint you provided is that it dies slowly. It seems to me if it were a diode, it would drop out more rapidly. Also, if it were one diode, you would probably not even notice, and what chances of multiple? If wiring in the alternator was expanding from heat and then shorting, again, I think it would be abrupt. So, I could see a connection heating up and slowly increasing in resistance causing the gradual failure. I guess you could run a controlled current through the rotor, then the stator and see what happens as it heats up, not the easiest test, but possible if you wish to troubleshoot that far. But before that, I would check if the brushes seem snug, maybe they are sticking as they heat up. Since the alternator shop, and you, did not find an alternator problem, maybe it is not the problem. Maybe there is a car wire connection/ground heating up and causing the decrease. And, although unlikely, but easiest to check, maybe your battery is bad. I have, on rare occasions had batteries make an alternator look bad. For the time it takes swap it out.
Tom

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Thanks John, but I have already eliminated the regulator by performing the test from the manual where you short the field negative to ground. My regulator is fairly new as is the wire harness. The alternator has not had a problem in the 25 years Iā€™ve owned the car till now.

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That sounds like a great idea. Do you have any part numbers for that alternator? Do you know where one can be obtained? Price?

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Thanks wayman, I do have a scope and nothing really looks unusual although I did not disconnect the battery as the article from your link states. Maybe I can try that and see what I get. Itā€™s just so much work getting things back together each time to be able to run it long enough to get really hot to reach the failure mode, that the frustration level is overflowing. :roll_eyes:

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Thanks Joe, but thatā€™s pretty much the case with the shop itā€™s at right now. Iā€™m in Southern California and considering the weight of this thing, it might cost that much just for shipping! :open_mouth:

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Thanks Osscarr, you may be on to something there. When I get it back I plan on tearing it down again to check where the diode heatsinks are bolted to the frame and the + post. I know that itā€™s not a problem with the wires soldered to the slip ring since even in the hot failure mode it is still pulling about 2 amps through the field winding.

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Tommd55 wrote:
ā€œI could see a connection heating up and slowly increasing in resistance causing the gradual failure.ā€

Thatā€™s about the only thing that makes any sense!
Thanks

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I suggest you not disconnect the battery. Just use AC coupling on the scope and expand the scale. Be sure to measure at the back of the alternator and use the - battery terminal as the common. There is enough resistance in the wiring to act as a current sense resistor. You will only be measuring mVs but they correspond to many amps.

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Steve, unfortunately I do not know the model #, but an alternator shop may have a cross reference guide that can locate it. I believe the 74-79 XJ 12 went to a different alternator, maybe thatā€™s a start. All I know is that the shop here in Dallas identified it as a Leece-Neville. The regulator is internal so the plug near aft of the battery intended for the external unit has been taped off and unit removed for as long as Iā€™e owned the car.

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WWayman, this is what I have already done and could not see anything out of the ordinary, that is, no missing peaks in the ripple.

Mollyoliver, you were very fortunate to get that alternator when you did. I have looked at the Leece-Neville website and they apparently no longer offer anything that uses the same frame as our Butec or the alternator that you have. All of their offerings have a somewhat different frame, that is they have cast in mounting tabs whereas ours are completely round with tapped holes to bolt on the mounting pieces. I believe this picture may be similar to what you may have as far as the regulator is concerned, but notice that the frame has the cast mounting tabs, so not exactly a drop in.

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Today when I go to pick up my alternator I will ask them about the Denso alternators being bi-directional or dedicated to CW or CCW. If they tell me they are bi-directional I think I will go that route. If they ARE handed, CW or CCW, then Iā€™m afraid Iā€™m still in a pickle since a new Denso is about $130 vs $430~$460 from the Jag specialists. Here we go again, decisions, decisions!

Hmmmmm :thinking:

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Steveā€¦try sending ground. Rememberā€¦most shops in the US send alternators to my guy in Paterson NJ. When they get it back, they tack on $300 and sell it to youā€¦for an overhaul !!! Not even a new one !
JJ

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Steve,
I have had and to some degree still have issues with my Butec.
One thing I did was to take the brush holder assembly off and measure it for resistance between the spade connectors for + & - . Due to corrosion, the resistance were much higher than the 0 point something I was expecting. I ended up redoing the connecting ā€œscrewsā€ in stainless, clean all parts with a glass fiber brush and used toothed washers to ensure good contact. I now have a generator that provides more charge that before. However, I still see a drop in voltage when I use fans, light and A/C.
Good luck and looking forward to hearing about your results ā€¦ Ole

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AFAIK, the only thing that is ā€œhandedā€ is the fanā€¦