alternator putting out 18v!!!

[TheDubs]

I have a Rv with a 82 6.2 chevy diesel in it.

I just replaced the alt in my rv about a month ago and it wasn't putting out enough volts. I found that the wire from the back of the alt had a bad connection on it so I replaced it. That seem to fix the problem.

Untill yesterday. We got stopped at a red light and the engine died. Looked at the batts and one was boiling and spewing batt acid. finally they got cooled down enough to get to a parking lot. I took the alt out and took it to auto zone and had it tested it was bad. Picked up another new alt hooked it up and it was giving me 18 volts off the back of the alt. and 17.5 at the isolator and 17.5 to the batts. No wonder I fryed the batts. I thought I might have got a bad alt again so I took that one back and had it tested and it was fine.

So i thought it might be the batts that were bad. I took them to auto zone and had them tested, 3 out of the 4 were bad. :( ( they were only 6 months old) I replaced those. And am still having the same problem. I cannot figure this out. all the cables to the batts are nice and tight.

I think im going to start at the wires going to the voltage regulator on the alt and see if they are fryed. and then check the ground going from the batts to the engine. I might also check the ground from the engine to the chassis too. I would think It has to be a grounding issue. Due to not having any place for the extra volts to go.

I am at a loss and can't figure it out any help would be great.

[DmaxMaverick]

Make sure all your batteries (4) are connected PARALLEL. If you get even one reversed, it will increase the system voltage, and cause all kinds of havoc on a 12V system (including everything you've experienced). Verify ALL of the (+) terminals are connected to the (+) cable(s), and all the (-) terminals are connected to ground.

Also, disconnect the shore power converter (AC and DC connections) and check the system voltage. When they fail, they can cause issues with the system voltage and alternator output (floating ground + GFCI interface).

[TheDubs]

Dmaxmaverick I checked all the cables and there fine.

I took the alt back to auto zone and they tested it and it was fine. but I insisted the give me a new one. They did and I also had them test that one and it was fine. Got it installed and the problem persists.

The alt that I have has the regulator built into it. It has what looks to be like a pos wire and a neg wire going to it in a harness that you plug into the alt. I jammed my volt meter into the pos wire coming out of the regulator harness and it gives me 12.63 volts with the engine running. I would assume its regulating just fine. Now for the pos on the back of the alt I get a reading of 18. and a reading of 17.5 at the isolator and 16 to 16.5 at the batt terminals. I have checked the ground from the batts to the frame and the frame to the engine. and they seem fine.

I have no clue whats going on and hope someone can help me figure it out.

[JohnC]

Where are you putting the ground of the volt meter? It sounds like the voltage regulator is seeing a different ground from the alternator.