Stranded!

[mel s]

Originally Posted by CaymanPilot

Arrived safely home yesterday with alternator disconnected, Trombetta bypassed and generator running the entire 400 mile trip. Thanks again to all contributors who supplied information for the workaround.
Now I am faced with correcting the problem. At this point I am not sure whether it is the alternator itself or an intermittent problem with the "sense" wire that connects to the alternator. It was suggested in this thread that the sense wire is connected to the alternator on one end and to the positive chassis battery terminal at the other end. I looked over my wiring schematics and can say that it "appears" to be true although I couldn't find a direct connection as the wire passes through several multi connector chassis connectors and it was impossible to trace it all the way through. So, I decided to test for battery voltage at the alternator end of the disconnected sense wire. Test results: With battery switches in the on position and the ignition switch in the off position there was zero volts between the sense wire and ground. With the battery switches in the on position and the ignition switch in the on position there was zero volts between the sense wire and ground. This tells me that either the sense wire is not connected to the positive terminal of the chassis battery or there is an open somewhere in that circuit. If the sense wire should be connected to the positive terminal of the chassis battery, then the next step should be to run a fused (external to the wiring loom) wire of the same gauge from the positive terminal of the chassis battery to the sense wire post on the alternator, start the engine and see if the over-voltage condition disappears.
Would appreciate any comments on my logic, suggestions for improving the procedure or confirmation on whether or not I am on the right track.
Would be very cool to have one thread that shows the issue, how to limp home and how to fix the problem when you get home for any future unfortunate motorhomers that experience the same issue I am experiencing.

CaymanPilot
My alternator has been charging the batteries correctly, (aka: as it should), for the last 4 years, (25,000+ miles), with a 14 gauge fused wire replacing the original sense wire, (which on my coach was, and still is, broken or somehow disconnected somewhere in the wire loom).

BTW, I'm happy to hear that you got home without additional problems.

Mel
'96 Safari, (148k miles)

[YC1]

To follow wires in these RV's is near impossible without an inexpensive tool most do it yourselfers should have. To chase that sense wire you would lift it off the alternator and put the tone sending device on it and ground. Then use the sniffer to follow the wire looms.
These work great for finding the poorly labeled fuses or hidden inline fuses. The prices of these are now dirt cheap compared to the first ones sold.
This is just an example of one. If you do any computer work you can get one with a cable tester for a few bucks more.

Network Telephone Phone Line Cable Tracker Tester with Pouch(Not include battery) - Circuit Testers - Amazon.com

Here is a schematic of an alternator with a separate regulator. It shows several fuses etc so you may have a simple fuse blown issue.

[CaymanPilot]

Thank you Twinboat, Mel and Myron for your valuable input. In the meantime I called Monaco (Allied) and they also verified that the alternator sense wire terminated on the positive terminal of the chassis battery. Since I had a little time and some lovely weather, I dug in to tracing the wire. I must have cut open 30 wire ties and got a pound of dirt in my eyes but I traced it successfully to the rear run panel where it terminated in a multi conductor connector which plugged in to a fuse panel with several other multi conductor connectors. With my VOM I figured out which fuse it was. The fuse was labeled "Alt Relay". Also connected to the fuse block were three 4 gauge positive battery cables and one negative battery cable. The fuse was fine as checked by VOM. One side of the fuse was connected to the "Alt Relay" wire and the other side was connected to ground. Yes, ground! It should have been connected to one of the positive battery cables. I removed the fuse panel so see if I could see why this happened but the fuse panel was a solid piece of plastic with no access to the innards. So, I cut the "Alt Relay" wire about 2 inches from the fuse panel and soldered an inline 5 amp fuse to it with a ring connector on the other end which I placed on one of the positive battery cables. Now, when I turned on the ignition switch I had 13.4 VDC between the alternator sense wire post and the alternator negative battery cable post. After starting the engine, all gauges showed normal. With the engine running the VOM showed 7.1 VDC between the alternator sense wire post and the alternator negative battery cable post. I remember my trusty alternator guy telling me that this is the way it should be. The volts shown at the alternator sense post should be half of what the alternator is putting out in volts. I don't understand this since the sense wire is connected to a 12VDC positive battery terminal. Can anyone give a simple explanation for this? We've come a long way with this thread and with this last piece of information we'll have a start to finish scenario for anyone who gets stranded with this problem so they can avoid the stress of breaking down on the side of the interstate, being towed to a RV repair facility and paying exorbitant prices for repair. I paid less than $10 for the inline fuse holder.

[TMan59]

This is just fascinating.
Things I will never try myself, but my gosh, you folks are my hero's!

[Podivin]

This has been one of the more useful/imformative threads (full of information I HOPE I never have to use). Thanks to all of the contributors of suggestions and good information, and to Cayman for not leaving us hanging as to what the 'correct' answer was. It's nice to see something come all the way to the end.

[twinboat]

I see that you did a work around, thats good.

Just thinking about the 4, 4 gauge wires. Could the grounded one belong on positive post in the battery compartment ?

Did this problem start after doing any battery work ?

I'm the type of guy that needs to know. I don't usually do a work around.

I worked in a big shop with a few guys who would just run new wires. When it was mine to fix, I would cut the wire out and find the problem.

[onechaddude]

Wow Steve, awesome work you've done there. I'm very glad I followed your thread. It will help knowing what you did and what to look for. This will probably end up helping many people.

I've followed since your first post when you broke down. I didn't post since I had nothing to offer to help you and i didn't want take your time reading meaningless stuff. I'm glad you made it home safely and also figured out your problem.

I look forward to hearing how your coach handled on the trip.

Chad

[YC1]

A few pictures would really help.

If you are saying you now have a fused lead on a wire connected directly to a battery supply point and have 7 volts you have a problem. A sound 12 volt source through a fuse should have 12 volts all along the way. But please read on.

I suspect your work around may not quite be the solution. Sorry to be the wet blanket here but as suggested you could be installing more problems than solving.

How did you determine that wire you traced is 100% the right one? If you were using the vom in the ohmeter mode you should have seen close to 0 ohms when testing if that wire went directly to ground. Lifting the end in question would have raised it to infinite.

Putting a fused 12 volts on that line should provide a solid 12 volts at the alternator.
That said. The alternator sense should not be a solid 12 volts but a regulated voltage. The wire you fused may be the input to the regulator and someone prior to you replaced the regulator and thought all was good because of the on board BIRD system keeping up the voltage. Or they just failed to mention that fact to you if you are not the first owner.

[YC1]

You may have cured the problem but inquiring minds just are never satisfied. If this is working for you now no one can argue with success. However there should be a regulator somewhere nearby and a part number on it would reveal a lot. I suspect you may have activated the regulator that has not worked since install.

Often customers leave out critical bits of information by accident or intention. I play a game called 20 questions. Keeping the customer near me while chasing the issue I tell them I will be asking many questions and often what might seem to be the same question. Asking the same question in a different way will sometimes dig out that tiny bit of information that is needed to diagnose the issue. Often they don't tell you they are not the first owner, or that it never worked, or they worked on it first.

With written forums it is much more difficult and on occasion I have connected with phone calls to solve some really difficult problems. Working with technicians for 40 years over the radio and when available the telephone the experience has really helped. It is great fun keeping the brain challenged now that I am retired. Keep them coming.

[CaymanPilot]

Originally Posted by YC1

A few pictures would really help.

If you are saying you now have a fused lead on a wire connected directly to a battery supply point and have 7 volts you have a problem. A sound 12 volt source through a fuse should have 12 volts all along the way. But please read on.

I suspect your work around may not quite be the solution. Sorry to be the wet blanket here but as suggested you could be installing more problems than solving.

How did you determine that wire you traced is 100% the right one? If you were using the vom in the ohmeter mode you should have seen close to 0 ohms when testing if that wire went directly to ground. Lifting the end in question would have raised it to infinite.

Putting a fused 12 volts on that line should provide a solid 12 volts at the alternator.
That said. The alternator sense should not be a solid 12 volts but a regulated voltage. The wire you fused may be the input to the regulator and someone prior to you replaced the regulator and thought all was good because of the on board BIRD system keeping up the voltage. Or they just failed to mention that fact to you if you are not the first owner.

Myron, you hit the nail on the head. Connecting what I thought was the alternator sense wire to a 12VDC source was not the correct solution. The next day after wiring the sense wire from the alternator to the positive battery cable, I wanted to move the motorhome to the storage shed. It started fine but then I immediately got the overvoltage (24VDC+) again so I shut it down. The inline fuse I installed on the sense wire was blown. I had verified that I was working with the correct wire 2 ways. 1. On both ends, it was labeled "ALT RELAY" and 2. I connected a length of 14 gauge wire to the disconnected alternator end and then checked for continuity between the ends of the two wires and came up with 0 ohms. It appeared that it had never been tampered with by the original owner. So, I removed the alternator and took it to my trusty alternator guy. He put it on the tester and said that the internal regulator was stuck open and that is why I was getting the over voltage. He said the 3 smaller terminals (one of which the ALT RELAY wire was connected to) are 7VAC (yes, AC) output. Those are not inputs for sensing anything. He said some manufacturers use them to run things like hour meters, etc. No wonder the fuse blew when one end was putting out 12VDC and the other end was putting out 7VAC. He also said the alternator will do its job with nothing connected to the 3 smaller terminals and that the internal regulator works on loads sensed at the large positive and negative alternator terminals. So, at this point I am waiting for him to fix the alternator internal regulator and I need to figure out what the "ALT SENSE" circuit does. Quite possibly, there may be nothing wrong with the ground on one side of the fuse for this circuit. I will dig in to my schematics tonight and try to find out what it does. I'm guessing that maybe the circuit uses a relay to turn on the ALT FAIL light on the dash or something similar to that. If you think I'm making a big mistake, please don't hesitate to throw on the wet blanket. At the time, I sure thought I was doing the right thing but now I see that it wasn't. Good thing I had the fuse in there! I sincerely appreciate all of your input. The more I learn about my motorhome, the more prepared I will be to handle whatever it throws at me.

PS - as soon as I get the alternator back, I will take some pictures and post them here.

[CaymanPilot]

Found this schematic of my alternator in my inbox, sent to me from Monaco (Allied). It clearly shows the three smaller terminals labeled "AC TERM-6V" in the schematic are not "sense" input terminals. I am not doubting that there are Monaco coaches out there, perhaps of earlier model years, that have a Leece Neville alternator with a sense wire. But mine does not have a sense wire. The wire connected to the middle 6VAC terminal is fused with a 5 amp fuse in the rear run bay and it energizes the ALT FAIL relay in the front run bay which turns on the ALT FAIL light on the dash if the alternator is not putting out voltage.
With this knowledge, I think I will put the ALT RELAY wire back the way it was, reinstall my newly rebuilt alternator when I get it back and all should be well. Of course I will report back here with the results of this plan. All comments welcome.

[TXduo]

Sounds like what I said in post #2 on this thread. Hope the field didn't overheat and cook itself when running wide open with the shorted regulator. Make sure that when you put it back on that you don't trap the internal regulator inside next to the engine block heat. Let it get some air circulation on the outside.

[YC1]

Nice work. Of course some would say "I told you so" but then you and the rest of us learned a lot more about your coach. You now know it does not have an external regulator and that the strange lower voltages are for things like alternator fail lights etc.

In the olden days using external regulators it was easy to test an alternator by just removing the field wire and connecting it to the battery. The alternator would go full tilt. You could open the output line and use that pulsating DC to run a drill or saw.

[TXduo]

Okay. Point taken. My apologies to all.