How does the Marelli alternator actually work? (Fixed!)

[bran100]

I'm goofing off with my 65amp Marelli alternator until I can pull the trigger on Marks', so in the meantime, I'm trying to understand exactly what is what and how it works. Specifically, how does voltage travel from the alternator through the stud at the 1 o'clock position in this photo? From what I remember, the backside of that stud isn't attached to anything, it's just routed through the housing, surrounded with an insulator, and then alongside the rectifier. I can't for the life of me understand how this can actually put out the 11.75volts that it's putting out. Yes, this is why I'm goofing around with it.

The voltage regulator is only a couple of years old from what I remember, so I'm thinking that's not the problem, but rather that stud that's routing through a somewhat cracked insulator, and difficult to get tight as there's no way to put a backing wrench on it. Brushes are a little worn, but don't look too bad as I think I remember changing those a couple of years ago too.

So how does this work?

[majicwrench]

That stud at 1oclock certainly had a wire on it, or on it's opposite end, about 10 oclock, something used to be there. Roughly, Current is fed to the brushes and into the rotor, where it build a magnetic field. That field passes thru the windings producing an ac voltage. The recitfier ( piece with fins from 10 oclock to 2 oclock) converts that to dc voltage, which flows out of the big wire on that stud.Regulator moniters voltage and when voltage get too high, it cuts down amount of current to brushes, magnetic field goes down, output volt goes down.
I would bet some sort of key on power goes to the small terminal at 4 oclock.
Does that help?
Keith

[bran100]

That helps a lot Keith. I think I'll have to take it apart again to inspect the other end of that bolt. It just spins freely right now. Hate doing it as I have to unsolder the rectifier, but I'll do that right now and report back.

Thanks a lot,
Brandon

[bran100]

There's definitely nothing attached to that stud on the inside either

Here's the backside


Does anyone have a Marelli 65amp alternator they can take a look at to tell me what, if anything is attached to that stud, aside from the external battery and starter connections?

BTW, I believe that exposed connector leads to the charging light on the dash and that exposed bolt hole at 10 o'clock is a phillips hold down screw for the rectifier. It also holds a black sheet metal cover over the assembly.

Thanks,
Brandon

[bran100]

I see lots of pics of rectifiers on Google image search, and most have a stud that looks attached to the rectifier, but I can't tell if it's actually attached to something. Does anyone have a rectifier handy that they can take a good picture of the stud? Front and back? What's it attached to?

I cant' imaging current passes via induction? That sounds like a far stretch.

Brandon

[majicwrench]

"aside form the external battery and stareter connections" that is the wire that is attaached to that stud. What else are you looking for?? There is no wire inside the alt hooked to the stud, the rectifier is hot. because of those three wires from the windings. To a certain extent, you could call it induction, the mag field in the rotor passes thru the windings in the stator and creates current.

[bran100]

Thanks, I was thinking there had to be something energizing that stud on the inside, but it sounds like it's some form of induction. Now to spray paint the housing and put it back together.

[bran100]

Took it completely apart, cleaned everything, spray painted with chrome and black paint, slapped it back together, and it's now working great! At one point, I found a rectifier wire that wasn't attached (again). I thought I did that while desoldering the wires, but it could be that was the problem all along. I'll never know, but I'm so glad it works, and now it's the best looking part of the engine compartment.


Thanks All!

Brandon

[ScoopMan]

Brandon, I got your email but your photos are not coming thru. Sounds like you fixed it so nevermind.... Congrats.....