e30 charging problem...

Check the warning light bulb and wiring. On many cars this supplies the field exciting volts. If it's not on with the engine stopped it's the first thing to check.

I thought about that... but according to Bentley they put a resister in parallel with the light in case the bulb goes... could still be the wiring though I suppose... but that's all in the instrument cluster replaced...

I'll double check and make sure the bulb is lit before the car is started and report back...

-Aaron

The voltage at the battery with the engine off should be around 12 volts. The voltage at the battery with the engine on should be around 14 volts. If this condition does not exist, your battery will not be charged.

You said that the voltage at the battery with the engine on was less than 12 volts. This is a clear indication that there is a problem in the charging circuitry.

A likely cause is a bad regulator, but you said that that you replaced it. It is most unlikely that two regulators would fail. Another likely cause is a problem with the alternator, but you said that someone checked it.

The light goes off when the alternator voltage is higher than battery voltage. This indicates that the alternator is working fine. By the way , that light and the resistor you mentioned is the only place in the instrument cluster which affects your problem.

There is a direct connection between the battery and alternator because the current is much too high to travel any path but the shortest. I suppose you did notice that the battery cable is much bigger than those in the instrument cluster.

Hence, I would check all of the connections and all of the battery to alternator cables. Jim

If you've replaced the cluster and the bulb still doesn't work, this points to a wiring fault. Two blown bulbs are a little too much of a coincidence. If you have the wiring diagram, you could provide a temporary ground or +12 volts (whichever it is) to the warning light terminal on the alternator. If it starts charging you've got it.

Well, I don't know if it is any help but I had a similar problem on my '91 a while back (Bench tesed fine in all conditions, warning light did not indicate fault, but yet the battery clearly died when the car was driven), but a regulator fixed the problem... and I suspect that the brushes were the only problem with it. All that to say that just 'cuz the alternator checks out doesn't mean it's good... really makes me wonder why bench test them, but that's a different question.

On a side note, I now have a regulator with worn out brushes and have been told that the brushes cannot be replaced in it. Is this true? if not, where can I get brushes? Thanks

Matt

There's bench testing and bench testing. One consists of putting the alternator on a bench and staring at it. The other involves an alternator test bench which runs it up with an electric motor and checks it properly

- including for maximum output, which is tricky to do without the proper facilities.

True, and mine was tested on such a bench. It was computerized and ran tests specific to the alternator specified. I have seen the times when a guy puts a belt and a volt meter on it, spins it up and says "yep, she's all good;" doesn't give me much confidence.

Matt

;-)

You might as well do this on the car if that's the limit of the test.

I heard this too... I think you can replace just the brushes, but it's a bit of a pain. I think they're riveted on, so you'd have to drill out the rivets and replace them with screws.

-Aaron

Well, sure enough the battery light wasn't lighting up. I reread some of the bentley troubleshooting steps and found something that I somehow completely missed before. They suggest removing the d+ (blue) wire from the alternator, turning on the ignition, and connecting it to ground. If the battery warning light lights up, all is well in the inst. cluster department, and it's something internal to the alternator.

The light lit up...

The real bitch of it is that I actually read Matt's prior thread quite a while ago (before bringing the alternator to the shop)... so I was wary of this whole bench-testing thing... When the guy tested it, I was completely satisified that there wasn't anything he could have done better. He loaded it up to like 30A, he ran it unloaded, everything checked out.

Thanks for all your help - I'll let you know what happends after I bring the alt. to the shop...

-Aaron

Of course you can replace the brushes, you get them at any starter/alternator place. They're like, a dollar. I went in with all sorts of part number and was told BOSCH units only use one part, here they are that's a dollar please.

You might need to do a bit of soldering but it's all very straightforward.

I did this on one of my cars a couple of years ago and made some notes, maybe this is helpful:

T'was the stator. The alternator guy says that Bosch stators have a thing with corrosion -- rust builts up in the fins on the stator and spread the fins out, and can short it with the wiring. So he replaced the stator and the bearings for $100.

Thanks again for your help!