I had this happen on my alternator recently. Was in the shop for 2 months trying to figure out the issue. Bosch alternator. Original voltage regulator had gone bad. Loss of charge after initial load.
I've owned 3 Champion generators over the past 10 or so years. The 1st one was actually a clearance unit from Tractor Supply that ran but didn't make power. I ended up calling the 1800 number not expecting much, but they talked me through some tests I could do and emailed me the troubleshooting tree. Ended up pretty easily figuring out it was a bad auto voltage regulator. Called Champion back and ordered the part for around $30. It came later that week and that generator has worked flawlessly for the last 10+ years.
It definitely saved me from having to buy a new alternator. For such a cheap part it’s a must do!
Today I replaced my voltage regulator and the issue is fixed. I did it while the car was on the air but you can also do it if you jack the car up on the street.
First remove the negative terminal then 3 13mm nuts after that 1 T20 then you can remove a protective cover then the other 3 T20 and then its drops itself.
You can see in the picture that one of the brushes is shorter than the other one I think that was the issue.
I also did a battery test and the result was ‘charging okay’ 806EN of the 850EN.
Here is the OEM number for the voltage regulator: A 003 154 65 06. Because Mercedes does not have the part anymore I bought it form ERA it was about €35 orso.
I just had this problem with my daily R, it has 141,000 miles and the battery light came on. The alternator really isn't that hard to remove so I just took it off. My issue was the brushes in the regulator were worn out. I bought some new brushes; I bought 2 sets for $11. Fairly easy job, just google Valeo alternator voltage regulator brush replacement and you get a few DIY videos. BTW my slip rings looked almost new, no grooves at all.
Make sure to use the Bosch part, not a cheap alternative, bad voltage regulators will ruin perfectly good batteries.
Did some digging and noticed that there is a crack on the voltage regulator on the back of the alternator - which is the original alternator that came from the factory in 1992. The fluctuation is not massive on the volt gauge. However, I have noticed that the volt meter does not read as high as I am used to. It's in the green - probably 13v. My previous car was always closer to 14. Also, even though the car starts on the first crank, you have to blip the throttle to get the alt light to turn off. I am thinking this fluctuation - even if it is just slight - could be a foundational gremlin to a plethora of potential CIS issues. Thoughts?
Most common failure on my V50 is the voltage regulator.
The best voltage regulator is the Bosch solid state:
https://www2.cip1.com/bos-30019/
In my personal experience new built generators, including Bosch, are of very low quality. I haven’t had one make it past a year.
Installed a new Bosch voltage regulator (VR) on the fire wall and had the following problem: the 61 terminal does not have ground so the warning lite does not go on. Also there is battery voltage at the D+ terminal and causing the generator to get hot. I just installed another new VR and have the same problem.
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