Dead alternator

Topic: Dead alternator (Read 1524 times) previous topic - next topic

Dead alternator

July 08, 2016, 04:19:01 pm

I suspect that my alternator has died. Actually I think it died last week, but with the generator running for a few minutes when we first started out it looked like I had a working alternator. Since the longest trip last week was 70 miles, there was no problem. Today, though, we went about 200 miles, and I didn't even try the generator. I ran the inverter to keep the refrigerator cool. The voltmeter on the dash showed just under 12 volts when we started, and was down to about 10 volts when we arrived here. I actually turned on the boost switch when we got fuel so that the transmission would shift from drive to neutral to reverse.

We're parked tail down, so getting underneath to get to the isolator could be interesting. I haven't been that skinny in 50 years. I'm thinking that, since we're parked until the end of September, I can take the alternator off and take it in to a shop to have it rebuilt. My thought is to disconnect the engine batteries, then take pictures of the alternator as it is, then try to convince it to come out of the engine compartment. Is this a logical sequence? What problems should I anticipate? I have the feeling that I'm going to have to figure out some way to support the alternator during the removal and reinstallation processes. What else?

Re: Dead alternator

Reply #1 – July 08, 2016, 04:31:59 pm

I did the same process when I took my alternator off. I would check the batteries to make sure there is no dead cell which may have started a chain reaction. Had my rebuilt for under a hundred, however, I did need three new batteries, 400.00 FRN's.

Re: Dead alternator

Reply #2 – July 08, 2016, 04:34:53 pm

David, you have the DD 6V92, correct? If so, the alternator is right up on top, front of the engine, under the bed, no need to get underneath. Really easy to R & R. I've done mine alone several times.

Re: Dead alternator

Reply #3 – July 08, 2016, 05:12:42 pm

Have you done the troubleshooting to verify your diagnosis that the alternator is the culprit?

Said another way, you need to rule out a loose or broken wire or bad isolator before concluding that it is the alternator.

Re: Dead alternator

Reply #4 – July 08, 2016, 05:25:41 pm

And maybe check the 'sense' wire.
After mine broke, the alternator was putting out 26 volts .
It had burnt battery cable end off at the isolator.
When I ask the mfg about the 26 volts. He said that was just at an idle, he said you can weld with it when the engine is turned up !
Hope you find something simple...............~JL~

Re: Dead alternator

Reply #5 – July 16, 2016, 03:47:08 pm

Thursday afternoon I completely disconnected the engine batteries. I checked the voltage on each one - 12.77 or 12.78 on each. Yes, I know that is low, but all they've had for a charger is the Trik-L-Start. This morning I checked them, and they are at 12.67 or 12.68. Remember that when I pulled in here a week ago I had to turn the boost switch on just so the transmission could be shifted from D to R and back again.

Picture 1 is of the isolator panel. The upper right is the engine battery terminal, and upper left is the house battery terminal.
Picture 2 is of the lower left of the isolator panel.
Picture 3 of of the lower right of the isolator panel.

With the batteries disconnected and engine OFF I expected to find no voltage on the upper right terminal, and that's what I found. I expected to see voltage on the upper left terminal (house batteries), however I saw none. I checked the house batteries, and they are showing 13.6 volts, but then the chargers are connected.

Picture 2 isn't as bright as I'd like it to be, but it looks like there are some circuit breakers there. There is also a relay barely visible. Picture 3 shows a relay on the right and there is another one hidden behind the bundle of wires in the center.

What, exactly, am I looking at on this panel? I'm thinking that I'm going to need someone to help me check the cables from the alternator since I don't think my arms are long enough. Also, I see TWO red cables coming from the alternator. It looks like one heads down toward the isolator panel, and the other one towards the curbside of the engine. Starter, maybe?

There is a smaller wire (12 ga maybe) coming from the alternator. I'm assuming that is the infamous sense wire. Where should I look for the other end of it?

Re: Dead alternator

Reply #6 – July 16, 2016, 04:10:32 pm

The wire from the sense terminal of the alternator can connect to any chassis battery point toward the battery from the battery isolator/downstream of the battery isolator.

So, what ever is easier-- common places are chassis battery post of the battery isolator, chassis battery positive terminal itself, chassis battery lug of the battery boost/combine solenoid. All are the same electrically at they are all connected by very large-gauge cables to the chassis battery.

Re: Dead alternator

Reply #7 – July 16, 2016, 04:17:45 pm

Thanks, Brett.

Re: Dead alternator

Reply #8 – July 16, 2016, 04:47:03 pm

Quote from: kb0zke – July 16, 2016, 03:47:08 pm

What, exactly, am I looking at on this panel?

David,

Lots of questions here.

Do you have the "Automotive Wiring Diagram" for your coach? For my '93 U280, it is drawing B-2126 - might be the same for your U300. It has a very clear diagram of the isolator board, in the bottom left corner, outlined in dotted lines. It shows the 2 relays, 2 circuit breakers, and 2 solenoids, plus of course the isolator. Should not be any question about what you are seeing on that panel...

The fact that you read zero voltage on the left post on the isolator is troubling. As you said, it should read same voltage as your coach (house) battery bank. So something not right there. A heavy 000 cable runs from one of the coach battery positive terminals to one post on the "boost" solenoid, then direct to isolator post. Not much that could go wrong there.

All of the connections in your photos look kinda cruddy. It certainly would not hurt to take them all apart, clean them up, and reassemble. At the same time, you can look at the ID tag on each cable, and make sure it is connected properly (according to the wiring diagram). Verify the correct placement of the alternator sense wire, as described by Brett.

You've got some strange stuff going on with your electric system. Starting with the basics - fully charged batteries, clean terminals, and proper connection points - will be a big help in pinning down the solution to your mysterious symptoms.

Re: Dead alternator

Reply #9 – July 16, 2016, 05:20:12 pm

Thanks for the diagram number, Chuck. I found it, and if I read it correctly, there is NO circuit breaker for the alternator. I also found an explanation of the two heavy gauge red cables from the alternator, so I know which cable is which. I'll head back underneath in a few minutes. I'm getting pictures of our just-born grandson now. First things first!

Re: Dead alternator

Reply #10 – July 16, 2016, 05:58:20 pm

Here's what I would do.

I would take the cable from the alternator to the isolator off the lug of the isolator, and also take off the cable and sense wire that goes to the start battery (through the boost solenoid) and I would bolt them together cutting the isolator completely out of the loop and now the alternator is directly charging only the start battery.

Then I would start the engine and if you get +13 volts at the start battery, it's the isolator and if you don't get +13 volts it's the alternator. Caveat: ......or cruddy connections.

Probably would take 15 minutes.

Re: Dead alternator

Reply #11 – July 16, 2016, 11:45:00 pm

I agree that looking at all those connections (big and small) have to come apart asap and clean them up and the larger lug ones need to be all nice and shiny copper. Spray with some electrical cleaner and put back together. The little 2 pin circuit ones also need that rust gone or better yet get new ones and replace. They can be bought in most Napa's etc. Some are 15 amp and maybe also 20 amp. All of the connections are bad. My coach sense wire comes from starter hot lug at solenoid to alternator.
JohnH

Re: Dead alternator

Reply #12 – August 06, 2016, 02:04:46 pm

This morning the weather was nice this morning, and Jo Ann wanted to go shopping, so I sent her on her way and disconnected all electricity from the coach (50A power OFF, all batteries disconnected), then headed underneath to clean up connections. All went well at first. I started at the top left and worked down and right. Went to put the cables back on the right stud on the right solenoid and the nut wouldn't go on. Took everything off again, took the solenoid out and sat down in the shade with the solenoid and nut. Nut went right on. Figures. Back underneath and put everything back together again. Little nut for the single wire on the front of that solenoid is missing. Back out to look through the collection. Close, but nothing exactly right. Just then Jo Ann called from Wal-Mart, so I told her to go look for a package of assorted small nuts and bolts. She found one. While I was waiting for her to come back, I noticed that one stud on the isolator panel was hiding behind a big bunch of wires. I missed it when I did the cables up there, so I decided to clean it while I waited. Only one cable on it, so it won't take long.

Gee, this nut is tight. Oops, I just broke the stud. Cable end was as shiny as the others were after I cleaned them, so I probably should have left it alone. Now what? There is maybe a quarter inch of stud still sticking out, Is there such a thing as a stud extender? Or do I need to buy a new isolator?

I haven't run the test that Twig suggested yet, so I suppose that I may need a new isolator anyway.

Re: Dead alternator

Reply #13 – August 06, 2016, 02:27:41 pm

Quote from: kb0zke – August 06, 2016, 02:04:46 pm

Is there such a thing as a stud extender?

Hmm, I've seen nuts that are shallow, but no clue if the threads would mate. I do know the DW has been looking for years.

Re: Dead alternator

Reply #14 – August 06, 2016, 04:01:12 pm

Welcome to my hell. So much for the 15 minutes.

Re: Dead alternator

Reply #15 – August 06, 2016, 04:19:41 pm

Went over to Ace a few minutes ago and found just what I was looking for - a giant nut that fits the threads I have. I can screw this thing onto the threads that are left, then screw a piece of threaded rod into the other side, slip on the cable, and attach a nut. Of course, now I have to go turn the power off again, disconnect the house batteries, crawl under and fix, etc. I think I'll take a nap instead, and let the refrigerator have a few hours of keeping the new groceries cool.

Re: Dead alternator

Reply #16 – August 06, 2016, 06:03:55 pm

Quote from: kb0zke – August 06, 2016, 02:04:46 pm

Gee, this nut is tight. Oops, I just broke the stud. Cable end was as shiny as the others were after I cleaned them, so I probably should have left it alone. Now what? There is maybe a quarter inch of stud still sticking out, Is there such a thing as a stud extender? Or do I need to buy a new isolator?

I haven't run the test that Twig suggested yet, so I suppose that I may need a new isolator anyway.

Not knowing anything about your year coach I can only say you could make an extender if the price of the isolater warrants it.
Take a screw or bolt larger than the stud, cut the head off it, drill and tap it the size of the stud, screw it on and enlarge the lug on the wire to fit over the new "stud"

Re: Dead alternator

Reply #17 – August 06, 2016, 08:43:27 pm

There is long nuts that you could screw on the broken stud and then screw a one inch of ready rod onto it then you are ready to
go. The maybe called ready rod extender but the name I'm not sure about. They are used in buildings to hang dropped ceilings.

Re: Dead alternator

Reply #18 – August 06, 2016, 10:07:05 pm

That's what I got at Ace. Unfortunately, it looks like the stud broke at an angle, so the long nut is arguing about going on. I'll try again tomorrow.

Re: Dead alternator

Reply #19 – August 07, 2016, 09:09:16 am

David,
That isolator looks like it might be the original one. Looks like the one in my '95. I think l would get a new one.

Re: Dead alternator

Reply #20 – August 07, 2016, 09:42:44 am

David,

X2 on John's recommendation (above).

Since you posted another thread asking about isolators, I guess you are thinking about getting a new one. I believe that is a GOOD idea! IF you have to move/drive the coach before you get the shiny new isolator installed, I don't think that will be any problem. My reasoning below:

I was looking at the photo you posted (3 weeks ago) of your isolator panel, and comparing it to mine (photo below). If you number the studs on the isolator 1-4 from left to right, then I assume it is number 3 that you broke off, because you said it was "hiding" behind a bundle of wires. This is the "extra" coach (house) battery stud. It is connected to stud #1 (primary coach battery) with a heavy red jumper cable.

If I am correct that you broke stud #3, and you have trouble repairing it, then you could probably get along fine without even having it hooked up. I believe the most prevalent theory on this Forum is that Foretravel used the jumper cable from stud #1 to stud #3 to "double up" the number of diodes controlling charging current going to the coach batteries. This is supposedly because the coach battery bank is bigger than the "start" battery bank, and will suck up more amps when being charged by the alternator.

If you are generally plugged in to shore power, and keep your coach batteries fully charged, then when you drive they will draw almost zero amps from the alternator. It won't matter if you are missing the "extra" coach battery stud on the isolator. Just remove the big jumper cable, and don't worry about fixing the broken stud. Instead, save your energy for deciding what new isolator to buy!

OR, if I'm wrong about which stud you broke, ignore everything I just said!

Re: Dead alternator

Reply #21 – August 16, 2016, 05:29:01 pm

I just checked the engine batteries prior to hooking everything up to run the test Twig suggested, and got the following readings: 12.40, 12.52, 12.38. All batteries have been completely disconnected from everything for a couple of weeks now. Are these readings close enough that I can rule out a dying battery?

Re: Dead alternator

Reply #22 – August 16, 2016, 05:47:05 pm

Those voltages suggest not fully charged. Youll need to load test them to ensure they are not weak. Anything will work as a load. Portable inverter with alligator clips, 12v work light, etc. harbor freight sells a load tester for $20 that will work well for testing.

100 Amp 6/12V Battery Load Tester

Re: Dead alternator

Reply #23 – August 16, 2016, 05:49:52 pm

rvlooker, I expected that the batteries would be a little low, as they have been disconnected completely for a couple of weeks now. I'm going to connect them now and let them charge before starting the engine.

Re: Dead alternator

Reply #24 – August 16, 2016, 06:12:30 pm

If they have been disconnected for a couple of weeks, those readings are fine.

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