Smart 451 mhd alternator excitation and alternator mounting system

[Sergiu]

Hi guys,

I need some advice.

 

This is my first post here. I have a bit of an unusual situation regarding the alternator and the electrical system with my 451 MHD from 2012. I tried looking up the topic, but none of the posts seem to answer my questions... I must mention that I'm not a mechanic or engineer, I just have some basic understanding of physics.

 

A few days ago, the battery warning light came on while returning from a trip (about 130 km). The warning light went out when I switched off all the lights, unplugged the phone charger and turned off the radio. It came back on after a while. Since I thought it to be prudent not to turn the ignition off, I just drove at a fixed speed to minimize gear changes and power consumption and to get as close to home as possible to minimize the towing distance. I made it home alright. The next day the car started normally. I drove it around the block with no issues. I even ventured out on a trip to the mechanic (about 7km through the city) with no issues. The error the on-board computer spat out was "No alternator excitation", but no warning lights in the dashboard. The error was cleared and the car started. He changed the belt to the alternator as we noticed the outer part of it was a bit chewed up. The car started ok, the connectors to the alternator seemed to be ok, the battery seemed to be fine.

 

The same day I had to take an unexpected trip out of town, about 260 km round trip. I knew it was risky but it was unavoidable. The same red battery warning light came back on. This time it did not go away after I switched off everything I possibly could. I had to stop for gas and had to turn the engine off. It wouldn't start at first. I pushed the car to the parking lot of the gas station and successfully started the car. I made it to the destination. While there, I turned the ignition on a few times and it started without a hitch all throughout the evening. The next day, on my way back, the warning light came back on as soon as I left town. I drove carefully about 110 km without any issues, and just as I got off the main road to take a 5 km shortcut through a village, I had to brake more frequently and even had to come to a complete stop going up a hill. The ABS warning light came on, the gear shifts were very late, the windows wouldn't open or close and I was stuck in 4th for a while. I pulled over. Tried the ignition again with no success and called a towtruck to the mechanic as it was the closest. The car did start when I arrived there.

 

As he did not have time to work on my car at that moment, I left it there. Later he called and said the alternator must be replaced and we sourced a second hand alternator. The problem I encountered was that the mounting system of the new (SH) alternator is different from the one I had on my car, as you can hopefully see in the pictures attached. I tried to find an exact copy of the alternator I had, but with no luck. There are new parts available, but none in Romania, and I would have to wait for a few weeks to get a replacement.

 

Now my questions are these: 1. Was it really the alternator that's at fault or maybe it's something else. The error was "no excitation". I know that alternators rarely break and my mechanic doesn't have much experience with these.

2. How can I find an exact replacement for my current alternator, with the required bushings and all. I know Mercedes made several revisions to the mounting system over the years.

3. Is it possible to fix the old alternator?

4. Can I change the casing form the old alternator and fit it on the new one?

5. Is it worth it to modify the new alternator so that it would fit exactly where the old one used to be? It would require milling the holes on the mounting brackets to make them bigger.

6. Is there something I am missing?

 

The "broken" one is on the right and it has a blue mark. The new SH one has a yellow mark.

 

Wow this post turned out to be a doozie... sorry about that.