Confusing Alternator/Charging Issues - Help!

[dishwab]

SOLVED: See post 9 for detailed description. TLDR: Bosch is sending out remanufactured alternators with bunk voltage regulators.

Hey R3V, so I’ve been trying to solve a charging system issue that has me pretty stumped. This is on an 89 325i with an M30B35 from a 92 735i.

A little background: last fall when driving home from work at night, the lights went dim and the car died. Jumped it the next day and drove it home, then to OReilly to get the alternator tested and it came back as a failed voltage regulator. I figured this is why my battery was dying with accessories running. About three weeks prior to this happening I snapped my main drive belt and had to get the car towed home, at which time I replaced the water pump and all 3 belts.

Fast forward to this week: pulled the car from winter storage and installed a remanufactured Bosch alternator from Bavauto. Got it all hooked up properly, took it to OReilly to test and once again the new alternator tested as failed due to a bad voltage regulator... I thought ok, bad out of the box.

They sent me a second reman. alternator, and this time after installing it I attempted to hook the battery back up and as soon as the negative battery cable touched the terminal, it created enough spark to melt the top of the terminal. I triple checked that everything was hooked up right, but every time I attempted to connect the battery ground, the same thing happened. I took the second new alternator out, put the first new one back in, and the sparking problem was eliminated. This leads me to believe there was an internal issue with the second new alternator.

I then swapped regulators between the two “new” alternators and reinstalled the first new one. Once again took it to OReilly, once again tested as failed voltage regulator. Now I’m confused... could it be that both reman. alternators are bad but in different ways??

Voltage readings with a multimeter are as follows:

Car off:

Battery: 12.5
Alternator: 12.5
Exciter: 0

Car running (no accessories)

Battery: 13.7
Alternator: 14.1
Exciter: 14.4

Car running (headlights, stereo, AC)

Battery: 13.2
Alternator: 13.9
Exciter: 14.1

No apparent change in voltage when I rev the engine. The battery light comes on with the key in position two and turns off when the car is running. I checked the engine to body ground and added a new alternator to body ground, both of which are clean and tight. Could it be that something I’m missing got screwed up when the drive belt initially snapped? Any ideas? I’m fairly bamboozled here and could use some help.

Edit: took the first reman. alternator (with second regulator) to autozone and it bench tested all good, including the VR. Not sure what to think still

Thanks

[06UZ]

Did you check timing belt and connected charging belt Is ıt tie enough?

[dishwab]

Did you check timing belt and connected charging belt Is ıt tie enough?

The main v belt is new yeah, water pump seems to be working fine so I’m pretty sure the belt is on properly.

[TobyB]

You have a lot of drop between the alternator and battery-
.7v may not SEEM like much, but the battery will charge pretty well
at 13.9, but not much at all at 13.2

If the alternator wire is good, solid and big, then next try metering around for grounds.
It's easy to meter voltage drop- set to millivolts and go from alt lug to batt terminal, and so
forth.
Don't overlook the battery connections themselves- a thin layer of lead oxide under
one is a pretty poor conductor.

I don't know what autozoneout uses to test 'regulator' function-
voltages tend to be pretty good indicators of that. if you're attentive.

fwiw,
t

[jeffnhiscars]

Then there's JLevie's often repeated post that he's had so many bad reman alternators that he stopped buying them

[dishwab]

You have a lot of drop between the alternator and battery-
.7v may not SEEM like much, but the battery will charge pretty well
at 13.9, but not much at all at 13.2

If the alternator wire is good, solid and big, then next try metering around for grounds.
It's easy to meter voltage drop- set to millivolts and go from alt lug to batt terminal, and so
forth.
Don't overlook the battery connections themselves- a thin layer of lead oxide under
one is a pretty poor conductor.

I don't know what autozoneout uses to test 'regulator' function-
voltages tend to be pretty good indicators of that. if you're attentive.

fwiw,
t

Thanks for the reply. I'm guessing that the voltage at the alternator should match the voltage at the battery if everything is operating properly – is that correct?

I scuffed the battery terminals with a scotchbrite pad and checked the ground and positive connections to make sure they were tight, and all seemed to be correct.

My battery light int he cluster is coming on with the key turned to ON, but the ABS light isn't. Could that light being burnt out effect the exciter circuit?

[AndrewBird]

ABS light won't have any effect.

IMO, I'd say Autozone's test is wrong and you are fine. Voltages look good. Maybe check the engine ground strap. Alternator grounds through the engine block.

I would charge the battery to full outside the car. A low/dead battery will put a LOT of load on an alternator and can fry it. Might be your only problem.

[dishwab]

ABS light won't have any effect.

IMO, I'd say Autozone's test is wrong and you are fine. Voltages look good. Maybe check the engine ground strap. Alternator grounds through the engine block.

I would charge the battery to full outside the car. A low/dead battery will put a LOT of load on an alternator and can fry it. Might be your only problem.

I had the battery on a charger prior to taking it up to the autozone for this most recent test. I also took it there out of the car and it read fine on their equipment (97% charge).

It worries me that the alternator bench tests properly, but as soon as I have it in the car, it's coming back with a bad voltage regulator.

I thought at first that their test could be wrong too considering I had just installed the new* alternator, but doesn't it seem like the voltage is dropping too much with the loads on for everything to be working properly?

[dishwab]

Well, after all this time I got to the bottom of it.

I went through 2 alternators from BavAuto and 1 from FCPEuro and all 3 of them were showing the exact same symptoms on a bench test.... all new remanufactures, all Bosch branded, rebuilt in Germany.

I found a local automotive electrical specialist who was able to give me some better info: when we bench tested them in his shop they were only making 13.7V at 30amps, and all the way down to 13.2V at 115 amps.

We swapped in a brand new Bosch voltage regulator and lo and behold it started working right away: 14.7V at 30 amps, 14.5V at 115 amps.

So – anyone reading this – I would be careful before installing a remanufactured Bosch alternator: at least the AL-148X model. It seems like they are replacing the brushes on the regulators but beyond that there is no sort of quality control to check whether the internals are working or not.

I contacted both vendors I purchased alternators from to let them know about the problem, hopefully they can contact someone at Bosch and get this issue figured out on their end