HELP, troubleshooting a 5 terminal alternator

[OrangeHair]

Does anyone know what the 5 terminals do on a 5 terminal alternator. My manual says I have,
1) + output terminal (seems obvious)
2) IND terminal (Think this is indicator but I don't know what it does)
3) Sensing terminal (?)
4) Positive suppression terminal (?)
5) ground (alternator casing)
I'm trying to figure out why I can't get my battery light to go off on my car (1992 Range Rover).

The background. I'm not all that experienced working on my own car but I am an engineer.

The battery light came on a few weeks ago. The battery was all corroded and at least 5 years old so I just went ahead and replaced it. Unfortunately the light remained on.

I knew the alternator was replaced 10-11 years ago. The next weekend, I found a rebuilt alternator at O'reillys for ~$130 so I just went ahead and put it in myself. The alternator looked exactly like the old one, had all the same connections, and it was easy to put in. The light went off for a few days but came back on slowly. Crap. I know the voltage regulator is inside the alternator so it should also be new.

10 years ago, around the same time I had the alternator replaced, I had the "leads" replaced because I was losing voltage between the alternator and the battery. I picked up and extra thick 12 guage cable to run between the alternator and the battery, still no luck.

About this time I decided to start using my brain a bit. My manual suggested measuring the voltage across the cables. After tracking down a digital meter from a neighbor it, there is no more than 50 milivolts drop on the postive side and the negative side. At one point I measured 13.8 volts from the positive on the alternator to the housing. I was hoping for 14.5v but my manual said 13.5 was ok. So today I went for a drive to see if it might charge up the battery. No luck. Then, the readings were a bit lower. My neighbor had one of those non-invasive amp meters that clamps around wire and we measured ~12 amps both at idle and 2000 rpms. Searching the internet it's clear I should be expecting ~100 amps.

So I come back to the question of what the other terminals are doing? Is it possible one of these is malfunctioning and throwing the whole system off?

On other detail is that there are "suppresion capacitors" that were part of the wiring harness that connects to the alternator. I have no idea what they do. They aren't on the electrical diagram which I've studied.

Thanks for any help.

 

[BigWill]

first thought: did you have the "new" alternator tested before installing?

Places like O'Reillys have decent warranties, but very high failure rate on rebuilt parts.

My guess is the rebuilt alternator is also bad. I would take it off, take it back in, and have it tested.

 

[Texas___Fight]

Or you could just drive up to Autozone and have them test it for you. Unless of course you like the extra work then you could take it off. While your at it take off your tires and take them with you and check the airpresure.

 

[OrangeHair]

Went back to Orielly's and watched them test it, it was just fine. They didn't hookup but 3 of the 5 terminals (ground, positive and one other). I'm going to test the voltage drop between the battery + and the rest of the car, next. I think if there is a significant drop powering the rest of the car, my battery light would come on.

Oh, BTW, maybe 10 amps is just fine. The alternator is 100 amps but certainly it wouldn't be putting that much out at all times!

 

[OrangeHair]

Ok, been tinkering today. When they tested the alternator they hooked up what my manual calls the IND or indicator terminal, the positive output and the ground. I disconnected all others and the car still runs fine. One interesting thing is that the IND terminal measures 18.2v while the output only 13.4v. From my wiring diagram it is clear that the battery light is connected to these two wires (and thus it is lit up by about 5v).

So my question now is whether this 18v is correct or not. My guess is it is not correct. I can't even imagine how I could get 18v on a 12v system! I need to know if this is causing the alternator to output a little low (13.4v) and not charge my battery?

Also, I was able to run the car off the alternator alone (disconnected the battery after starting the car). It sputtered a bit when I turned on the radio, lights, and reved the engine. Not sure if that's a bad thing. It would seem the battery would help smooth out any surges in the required power.

 

[accuratehorn]

I don't know exactly how that five wire system works, but...
a) do not run the car with the battery disconnected, off the alternator alone. It will charge the maximum amount it can put out all the time, which is about 18 volts, and either burn itself out, or burn out other items on the car, like oxygen sensor heaters or electronic control units.
b) test the battery, some new ones can have bad plates, or internal shorts. If the battery shows a charge of over 14.5, it is defective.
c) if the alternator is really putting out 18 volts, it is putting out the maximum all the time. This is usually because the voltage regulator is defective, but it may be for some other reason, like not being grounded well. Add a ground wire between the alternator and chassis, alternator and engine, engine and chassis, and check the battery cables to make sure they didn't partially break while changing the battery, and clean them where they attach to the ground. You can just hook jumper cables to the ground of the battery and the engine, chassis and alternator case to see if anything changes.
d) rebuilt alternators use very cheap parts sometimes, especially the voltage regulators, and this is the most likely thing to be the problem.
e) Texas Alternator and Starter Service on IH-35 between Rundberg and Braker on the northbound feeder road is a good place to take the alternator for bench testing. They have been doing this for many years.

 

[OrangeHair]

I went by autozone today and they said everything checked out. The battery was fully charged with 12.8v. Once we started the car, the battery it was reading steady at 13.3v. So it's at least charging a bit, although I would feel more comfortable if it read 14.5v.

Thanks for all the points accuratehorn. I won't run the car without the battery again! The alternator is not putting out 18v, its the indicator terminal. The alternator is putting out more like 13.3v. I'm starting to think voltage regulator is just a cheap piece of junk and the indicator terminal is falsely reading high. From what I read online last night, if the battery light burns out (or I take it out) the alternator won't work. The battery light should come on every time you turn the key and then after a few seconds the light will go off.

Here's why. The battery light is hooked to the battery on one side and the alternator on the other side (actually the indicator port which tells you the voltage of the alternator). Once everything is on, there should be no difference between the battery and alternator because they are both putting out 12-13 volts (thus the light would be off). But when the car is off the alternator is putting out zero volts but the battery is still at 12.6v so the bulb lights up. So right when you turn the key, some current flows from the battery through the bulb to the alternator. Here's the interesting part, this current is necessary to get the electromagnets working in the alternator, otherwise it would just be spinning (with all those coils of copper wire) but with no electric and magnetic fields. Once the alternator starts producing its own power the electromagnets are self sustaining. The alternator and battery are now both reading 12-13 volts so there little if any voltage across the light and it goes off.

In my case the indicator terminal is malfunctioning and putting out a voltage higher than the alternator is actually charging. So it appears as though there is a problem when there is none. I could just move the bulb wire over to the charging terminal of the alternator (so it would read the proper voltage) but then the indicator terminal would be disconnected at startup and the alternator would never kick on.

 

[accuratehorn]

There are some cars that require voltage to go through the dash warning light for the charging system to work-Chevrolets used to be like that, don't know if they still work that way.
So that is probably correct.
It sounds like the IND terminal is getting the full amount the alternator puts out before going through the regulator, instead of after going through the regulator-but I don't know that this is incorrect, sounds like it would be, though.
Then when testing the alternator, it will only put out what the battery needs to keep it at 12 volts. You have to put it under a load to get it to put out the max, which should be 14.2 volts or so. Maybe they didn't do this at Autozone.
If the max is only a little over 13 volts, it may not keep the battery up at night with the headlights and A/C and your eight video terminals showing Debbie Does Dallas during a lengthy road trip.

 

[BigWill]

Mister Peepers!