Hello everyone! Does anyone in here have any experience with older Mecc Alte generators?

So, im trying to revive this old diesel genset. Imo the whole unit is basically trash, it's an old marine generator and the sea did not let it go without a fight. Corrosion is rampant, as you see in the pictures. But my customer really wants me to fix this unit, something about his father having worked on it or whatever. And like a miracle, all insulation tests are fine, so maybe there is hope after all?

But the AVR seems dodgy to say the least. I dont trust it, and i dont want any overvoltage events ruining his equipment in the future. And i need to change the output voltage from 400Vac to 230Vac anyway, so im replacing the old AVR. But im very confused with the wiring, and i'd like to have a general understanding on how this actually works before i start experimenting with it.

I made a wiring diagram showing the old wiring, to my best knowledge. Unlike any other AVR i've ever worked on, there does not seem to be any feeback of the actual output voltage to the AVR. Im assuming the "S" winding, being fused and having thicker wires, is for powering the AVR itself. Then the 8 ohm load must be the windings in the magnetizing field stator, this being a brushless generator. Unfortunately i dont have a proper instrument which can measure inductance on hand right now, so i can only measure resistance.

But then there's the current transformer thing, connected to its own 8 ohm load. Could there be two separate windings in the magnetizing field stator? it's so weird. Im tempted to connect a variable dc supply to these 8 ohm loads while the machine is running and see what happends, but the pucker factor is a bit too high still.

Anyone want to weigh in on this? Im looking forward to hearing from you.

Thank you all for your attention, i wish you a nice day.

 

Hello everyone! Does anyone in here have any experience with older Mecc Alte generators?

So, im trying to revive this old diesel genset. Imo the whole unit is basically trash, it's an old marine generator and the sea did not let it go without a fight. Corrosion is rampant, as you see in the pictures. But my customer really wants me to fix this unit, something about his father having worked on it or whatever. And like a miracle, all insulation tests are fine, so maybe there is hope after all?

But the AVR seems dodgy to say the least. I dont trust it, and i dont want any overvoltage events ruining his equipment in the future. And i need to change the output voltage from 400Vac to 230Vac anyway, so im replacing the old AVR. But im very confused with the wiring, and i'd like to have a general understanding on how this actually works before i start experimenting with it.

I made a wiring diagram showing the old wiring, to my best knowledge. Unlike any other AVR i've ever worked on, there does not seem to be any feeback of the actual output voltage to the AVR. Im assuming the "S" winding, being fused and having thicker wires, is for powering the AVR itself. Then the 8 ohm load must be the windings in the magnetizing field stator, this being a brushless generator. Unfortunately i dont have a proper instrument which can measure inductance on hand right now, so i can only measure resistance.

But then there's the current transformer thing, connected to its own 8 ohm load. Could there be two separate windings in the magnetizing field stator? it's so weird. Im tempted to connect a variable dc supply to these 8 ohm loads while the machine is running and see what happends, but the pucker factor is a bit too high still.

Anyone want to weigh in on this? Im looking forward to hearing from you.

Thank you all for your attention, i wish you a nice day.

I think you are right that the generator has two field windings. A-B supply for avr is probably also used for voltage measurement.
Mystery terminals I guess are used for starting magnetization.
I made a drawing, does that make sense?

 

OK, I just figured it out: AVR= Alternator Voltage Regulator. The real puzzle is that I see diodes in the photo of the alternator. NEXT, given the level of complexity, I suggest seeking a service manual for the system.

Nobody has been "working on it", they were GOOFING AROUND WITH IT!!. Until you understand the system, no reason to disconnect wires, unless you are going to scrap it and start over.

If you can locate a suitable Voltage Regulator, then you will need to determine what voltages the actual alternator delivered. So if nothing else, you need to discover what voltages the system actaually delivered when it was working.

 

Found this old MeccAlte instruction, may be of help when changing to new AVR.

 

Thank you both for your replies.

BVSM:
Yes, your drawing makes a bit more sense than mine. With two separate field windings, i guess that means the true magnetization current in the rotor is a result of the sum of the current in the two windings. I could apply a small current to each of them with the machine running, and see if they both produce the same output voltage or if one contributes more than the other. I checked a manual for a Stamford avr, and it specified ca 8 ohm resistance for the field winding. So it cant power both coils in series or paralell, guess i will have to choose one.

I still dont understand how the old avr measures the generators output voltage though. The "either A or B" wires are just that, either A or B. With my crappy instrument i cant verify which version is correct. But that is just a single phase. Im starting to wonder if one of the screws holding the avr could be connected internally as a ground reference? I'll have a look at it tomorrow.

And thank you for the pdf.


MisterBill2:
A service manual would be great, but the only piece of documentation i've seen so far is the one BVSM just posted. There is not much info on this unit available on the internet.

I realize now that the pictures with all the wires disconnected might have been misleading. I disconnected them myself so i could test the engine without needing to worry about the generator. I've added a picture of what it looked like before.

The output voltage was 380V TN, 50Hz.

And i believe the correct acronym is Automatic Voltage Regulator, but that is not important of course.


Thank you, and a wonderful sunday to you both.

 

In my book, ALL "Voltage Regulators" are automatic, and if it is not automatic then it is a "voltage adjuster. " And certainly voltage adjusters were more common in the realm of steam engine powered generator power plants. I saw all about that in an antique book a bunch of years ago, every detail about what was required to provide a generator for providing electricity to a town. It started with the description of the foundation requirements, as it was a total collection of details. Entertaining to read and see how far things ghave come.