24v (S50) intermittent charging issue

[xveganxcowboyx]

The current state of things: A big pot hole recently sent my radiator in to my power steering pump. While driving I had battery voltage, but occasionally I could feel the alternator kick in (sudden drag on the engine) and the voltage would come up to ~13.5 showing the alternator was doing it's job. I got a new radiator, finished prepping the car for spring and took it out. No charging whatsoever. The alternator was just rebuilt and the battery is good. With the intermittent issue I feel like the problem has to be in the system which triggers the alternator, but I don't know a ton about it. If memory serves it is triggered by battery voltage from the smaller wire which runs to the alternator and that this may be run through the gauge cluster (?)..... I doubt it is related by my cluster needs a new battery on the SI board, but otherwise functions ok.



Some backround info which may help....this is not the first charging issue I have had.

The PO said the alternator was rebuilt, but my local shop said the brushes were toast. I had it rebuilt. It mostly charged well, but every once in a while wouldn't start charging until I revved the engine or restarted the car. The ground at the batter has been cleaned looks good. The hood strap ground is broken and the large ground cable in the engine bay is missing it's rubber/plastic coating and probably has some corrosion. The voltage drop with accessories on was higher than I would like to see so I assume the grounds need to be redone. Interior check lights are useless as the car is old and German.

Any info on the best test procedures or most likely culprits is appreciated. It's not time sensitive as I have a truck and bikes, but it's nice out and I would really like to drive my E30.

[Malice]

How isthe harness setup? C101 spliced onto e36 harness or adapter harness? Check for voltage at pin 1 in c101. Thats the circuit that excites the alternator.

[xveganxcowboyx]

It's an adaptor. Nice big round twist lock plugs.

[Malice]

Well check in your c101 side the pin 1. Solid blue wire. Or just check it down at the alternator.

[xveganxcowboyx]

With the car running and a battery charger on, the main line to the alternator showed 12.2 volts. The smaller trigger line showed 11.3 volts.

[xveganxcowboyx]

So I applied battery voltage directly to the trigger line on the alternator and still got no charging. Should I be assuming this is an alternator issue or is there anything else worth checking?

[xveganxcowboyx]

So it may be a little early for an update, but I keep hoping someone will chime in with new insight. I put the key in the on position and did not see a battery light, but I pulled the cluster and checked the bulb. It is fine. I am keeping the cluster out until my new SI board batteries arrive so it will be a few days before I play with anything else, but this adds a new level to the problem. Power is obviously flowing through if the exciter circuit is seeing 11+ volts.

[Gregs///M]

The SI board has nothing to do with the charging circuit. I would test the resistance between the alternator and chassis ground, it should have low resistance. Don't over estimate how important the engine ground is. If this ground is oxidized, oily, or loose it can cause similar problems to what you are experiencing. The cable itself could also look perfectly fine but the connection points to the frame or engine side could be oxidized where you would not see it. The cable must be removed and inspected and all contact points cleaned.

[xveganxcowboyx]

The SI board has nothing to do with the charging circuit. I would test the resistance between the alternator and chassis ground, it should have low resistance. Don't over estimate how important the engine ground is. If this ground is oxidized, oily, or loose it can cause similar problems to what you are experiencing. The cable itself could also look perfectly fine but the connection points to the frame or engine side could be oxidized where you would not see it. The cable must be removed and inspected and all contact points cleaned.

That ground looks pretty bad. I did temporarily run a large gauge wire from the chassis to the alternator housing just to see if it helped, but I will replace that ground permanently.

That has been on my to do list anyway. I had some of Flickr of my headlights (hid) that already had me worrying about grounds.

Thanks!

[xveganxcowboyx]

More updates. I changed the chassis to engine ground and cleaned and applied dielectric grease to the others. I soldered in new SI batteries and put the cluster back together. Still no charge, the battery light does not come on with the key, and now I have no tach or economy gauge. Ugh.

The alternator will be coming out this week to be tested.

[xveganxcowboyx]

Well, this mystery problem has been solved. The epoxy used in rebuilding the alternator let go and wires separated inside. The rebuilder (quite a veteran) suggested that high revs or heat could cause it, but I do not have either of those problems. The next big question is why did it separate?

[Malice]

A gazillion heat cycles.

[xveganxcowboyx]

A gazillion heat cycles.

Well, it's probably had less than 40 heat cycles since the rebuild. It was fresh epoxy that split. Strange situation. I will discuss it with the rebuilder more when I pick it up. He will probably open it up and walk me through the problems so hopefully I will learn something useful about potential causes.

In the mean time I picked up a parts store rebuilt alternator to get my car working while I wait for the proper rebuild. I'd like to go to cars and coffee tomorrow morning and taking the E30 would be more fun than the bikes.