Strange Voltage Problems

[Michael666]

Sounding like it is the alternator and/or voltage regulator. The Voltage regulator is under the end cover and is replaceable for ~10% of what a OEM alternator cost.

It can't be the regulator. I just put in a new one, as said in my original post. Hopefully the (most likely broken) alternator didn't damage the new regulator

[SuperHerman]

Can you post the part numbers of your original regulator and the replacement? I know Volvo had an issue for certain regulators during your time frame - your car may not be affected or it may. Worth looking into. Maybe prior owner put a wrong alternator/regulator into the car. Also possible you installed a defective regulator even though it was new. Would not hurt to run some part numbers through the computer to double check.

If I recall correctly there are some other electronics on the alternator that may be the issue that don't get swapped out with the regulator/brush assembly (then again it may be for a different car I handled).

I would also swap the relays around in the CEM - like for like and see if the issue is resolved (beware you may have moved issues to another systems).

Checking out your CEM and wiring would not hurt.

[Michael666]

So, an update for now..I took the alternator out and when I get the chance I'm going to have it tested.

the Voltage Regulator(s) that were installed on the car, original and by the previous owner, are both Bosch F 00M A45 211. I installed a Hitachi Regulator 2500604. All are to Volvo spec OEN 8637851

[SuperHerman]

Those regulator numbers check out. Three regulators points to a problem with the alternator, but not regulator(s). It could be another electronic component, but stick with the alternator testing for now.

Are you confident of your testing of the battery? Has the same battery been through all three regulators?

[Michael666]

I have two questions regarding the alternator.
1. What is the small cable used for and could a break cause the alternator to stop charging?
2. Any way to bench test the alternator by myself using a multimeter?
I have very little time and when I do the shops are closed. Also my budget is very small, so a new Bosch alternator (400+€) is too much

[RickHaleParker]

1. What is the small cable used for and could a break cause the alternator to stop charging?

The larger wire carries the current to the battery. If it breaks, no charge transfer to the battery.

2. Anyway to bench test the alternator by myself using a multimeter?

Not really, It need to be bench tested when the alternator is spinning and loaded.

You should be able to find a remanufactured alternator for way less then 400€. Remanufactured from a reputable source is as good as new.

[SuperHerman]

The small wire goes to some module - based on its signal the module controls charging. Which module I don't know.

As far as testing - you did the main testing already. The only other easy test I know of with the alternator out is to hook up one probe to the positive post and the other to the casing with your VOM on Diode function - see what if anything it reads. Then flip the positive and negative probes around and check the reading. Only one side should provide a reading. If both sides do you have an issue. If you don't have a Diode setting you can use the Ohm scale but the values will be really small - but the same rules apply as if you were testing a diode - flow should be in only one direction.

I don't recall your alternator, but it should have diodes on the coil windings (stator). Half should go one way and the other half the other way. I assume their function is to turn the AC current into DC. If you can find these you should be able to test each one and see if one or more are bad. I have a visual picture of an alternator I played with, but don't recall from what car. I do recall I had to take off some pieces to get to it - but nothing that was destructive. You may also be able to test the individual windings for open or short.

Other test I found is this one from Axle Addict -
"3. Checking for a Bad Diode

Usually, a bad alternator diode will cause your headlights or instrument panel lights to flicker or dim and, sometimes, drain battery power overnight, or in minutes.

* To check for a possible bad alternator diode, switch your voltmeter to a low setting on the AC (alternating current) voltage scale.
* With the engine running, touch the meter probes to the battery terminals.
* Your voltmeter should read 0 AC volts.

Any amount of AC voltage would indicate a bad diode, so you'll need to replace the alternator."

I don't know if the regulator comes into play on this test - if it does the results will reveal a problem, which you already know.

[Michael666]

I did the diode test and everything checks out fine. One direction nothing the other 602. So they seem to be fine.
About that wire...mine has a strange plastic clip on it that cuts the wire a bit which allows a connection with another wire. But that wire ends nowhere and is only 2cm long. Maybe that causes the module to send a message to the alternator regulator to not charge...?
Annoyed that I did not take the clip of earlier to see if that wire is the problem.

[SuperHerman]

Take a picture of what you have and post it. Will make it much easier to help you out.

[Michael666]

That's the plastic part I was talking about