Golf3 TD, Valea LiMa excitation current missing

The 50A Valea alternator (LiMa) on my AAZ engine failed, so I found a refurbished, almost identical 70A Valea LiMa for sale online.
From the beginning, this vehicle had a problem where it only started charging when the engine speed was slightly above 1400 RPM (symptoms: the tachometer didn't work, and the oil level warning light blinked).
After checking all possible causes: The dashboard instrument was tested by being replaced, but the problem persisted. The cables from the dashboard instrument to the excitation terminal on the alternator were checked for continuity and resistance, and were found to be completely fine (no loose connections) and had low resistance. An additional ground wire was run from the alternator, but this didn't solve the problem. The return was not accepted. However, since the alternator reliably charged after a brief burst of acceleration and otherwise functioned perfectly, I decided to live with it, especially since I couldn't open it to check or measure its internal components. Now, after three years, the speed required for self-excitation has increased significantly (to about 2,000 rpm) within just a few weeks, and now it's not charging at all. Does anyone have any suggestions for what I could do before I try to get another one?

I don't know the individual part prices for the AAZ engine. For my vehicles (Passat 3C with BMP engine and Galaxy/Sharan 7M with BTB engine), used water pumps were available from €25 including shipping. I didn't really try to adjust the old bra anymore; I just replaced it.

If you still want to investigate, you should at least post the terminal markings of the alternator. With the older type, it might require external excitation. That's the wire you checked with the multimeter. Apply a small voltage +12V using a small light bulb (or other resistor) and check if a charge occurs.

"Previously, it would have self-excited at higher speeds. However, I cannot explain why the speed threshold required for this self-excitation has now increased. It's possible that the alternator has had a problem with excitation from the beginning and has now completely failed." You can test each individual component (4 windings, slip ring, 6-9 diodes, regulator), but I wouldn't bother doing that given the used price mentioned above.

Regards,
Guste.

Does the excitation voltage reach terminal 61 when the ignition is turned on?

Rüdi wrote:

Does the excitation voltage reach terminal 61 when the ignition is on?

Yes. I suspect a broken cable in the alternator (61) or a faulty regulator. The first thing I checked was the connection to the speedometer, because there are many potential sources of error there (intermediate connectors, cable breaks).
I think I'll just buy a new one that fits. The prices are okay, and frankly, it's probably not worth the hassle of trying to fix it, just to satisfy my curiosity. It still bothers me a bit that a regular workshop would limit itself to just swapping parts...

Tip: Try to get a Bosch starter, and I would avoid Valeo starters and alternators. Bosch products often have the advantage that you can sometimes salvage parts from two broken ones of different sizes or designs to create a working one, which has saved me more than once. I rarely throw anything away.

Thank you for the tip.

Hello!

By the way, I share the same negative opinion about Valeo.

It's been many years, but they used to have plastic rings coated with copper as brushes for the carbon contacts. It would occasionally peel off, and then the battery would be ruined.
You could still repair that Bosch twice, and you could adjust the carbon brushes.

Furthermore, regarding the charging control:
It's been a very long time, but with the Golf 2 diesel, this sometimes happened as well, when the idle speed was set too low.
that the charging indicator light was illuminated after the device started.
She just needed a quick burst of acceleration, and then she was gone.
That was considered normal, and it was the case for many cars. So, at least in my workplace, and those were already quite old cars back then.

What happens if terminal 61 was directly connected to the battery?

Take a 5-watt light bulb and temporarily connect one end to the battery and the other end to the D+ terminal on the alternator. If the lamp turns off immediately after starting and the alternator then immediately starts charging, you have a problem with the pre-excitation.