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Old 06-23-2015, 04:29 PM   #29
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Quote:
Originally Posted by Loren Rice View Post
Castrol
It could be just a normal death. But could also be that your batteries were on the low side and the alternator has output capabilities greater than your isolator resulting in it's death. So the previous owner could have driven and used the mh with no problems cause he had the batteries more fully charge and didn't pull all the amps that you did.

So when you replace the isolator make sure you know the output rating of your alternator and buy an isolator of whose capacity or greater than the alternator.

My mh doesn't have an isolator -- just a big relay that joins the two battery banks when the engine is running. I don't have remote sensing. But you need remote sensing cause there's a 7/10 volt drop across the isolator coupled with wire losses (which can be surprisingly large) by the time you get to your batteries. some one switched my rig over to a single output alternator (internal sensing) and so it doesn't try to over charge because there is close to a volt drop to the batteries and it just doesn't see all that load. That said I usually have my batteries nearly charged cause of my photovoltaic. Maybe I would have an alternator problem if all my batteries got on the low side.
I killed an alternator in a different mh a few years ago. What I learned is, that your starting battery should be nearly charged before starting off. This is because in a mh with all those house battery banks as well, adds a lot of load that some alternators aren't up to putting out full out put as long as necessary to bring up all those batteries.
So if you put in a remote sensing ckt it probably will be connected to your starting batteries, very close to the batteries because as I mentioned earlier wire, even heavy wire will have a voltage drop across it and to charge batteries the voltage needs to get to 13.8 min and usually is 14.5. That sensing wire will cause the alternator to put out perhaps 15.5 to get 14.5 at the battery terminal. With a isolator the voltage needs to be 16.2 at the alternator to get 14.5 a the battery post. Gets complicated doesn't it?

Hope this helps
Loren
Okay so that's very likely what the extra wire is on the chassis battery. I will see if I can locate where that goes and I'm betting it needs to be on the remote sensing lug?

Yes, very complicated but I'm willing to learn. I pretty much spend every night crawling around in and under this thing trying to figure it all out. There is so much that needs TLC and repair it's almost daunting. Almost. If I can get this alternator issue licked, the rest will be cake.
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Old 06-23-2015, 04:30 PM   #30
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The S wire needs to come from the engine battery, not the batt. post on the alternator.


It may be there, with a blown fuse. They could have tapped off the starter battery cable.
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Old 06-23-2015, 05:04 PM   #31
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Okay so here's what I've got.

I've got 12 volts on the black wire. 0 volts on the blue. 0 volts on the red. And 12 volts on the large lug which is the one that goes to the isolator. I'm swapping the black and blue wires.

http://i30.photobucket.com/albums/c3...pspno3vaju.jpg
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Old 06-23-2015, 05:10 PM   #32
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Of the 2, 0 volt wires, see if one goes hot with the key on. That should go to the I terminal.
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Old 06-23-2015, 05:13 PM   #33
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Yep. The blue one goes hot with the key on.
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Old 06-23-2015, 05:37 PM   #34
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Okay here's where I am...

I swapped wires. Started coach. Still no tach and still not showing volts on gauge. Measurement on isolator shows same.

Until I jumper it. And I just jumpered the posts momentarily. I heard the alternator kick in and I took the jumper off to get my dvom. When I walked up front the tach is working. Alt Fail light is off. The gauge shows charging. I've got charging at the batteries and the isolator.

But, if I turn it off and start it again, it goes back to the previous setting. Unless I jumper it briefly and then everything goes back to full working mode.
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Old 06-23-2015, 05:49 PM   #35
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It sure is cool to see the tach working. That's a huge leap forward so far.
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Old 06-23-2015, 05:51 PM   #36
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So does that mean the isolator is the kaput problem now that it is wired correctly?
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Old 06-23-2015, 06:07 PM   #37
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Still not right if a quick jump gets it going, the isolator is ok, at least half of is.

Your jumping sent 12 back to the alt., activating it.

Try starting it and revving the engine. It may kick in, like the old Delcos.
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Old 06-23-2015, 06:08 PM   #38
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Just watch that is doesn't overcharge.
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Old 06-23-2015, 06:11 PM   #39
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I'm getting a solid 14v at the batteries. Before I jumpered it I gave it a little rev. When I get to about 2000 rpm the tach comes in and the alt fail light dims a little. As soon as I drop below 2000 rpm the tach drops dead and the alt fail light is bright.
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Old 06-23-2015, 06:47 PM   #40
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If you have 12 volts to the S post , you may have a bad regulator.

Does the switched wire go to the I post?

The screwed up wires could have blew something.
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Old 06-23-2015, 08:19 PM   #41
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Okay here's where I am...

I swapped wires. Started coach. Still no tach and still not showing volts on gauge. Measurement on isolator shows same.

Until I jumper it. And I just jumpered the posts momentarily. I heard the alternator kick in and I took the jumper off to get my dvom. When I walked up front the tach is working. Alt Fail light is off. The gauge shows charging. I've got charging at the batteries and the isolator.

But, if I turn it off and start it again, it goes back to the previous setting. Unless I jumper it briefly and then everything goes back to full working mode.
I'm relying on a fuzzy, aged memory, but I had problems with a 93 Dynasty which had its alternator replaced with an "equivalent" one. There were TWO problems, that resulted from the fact that the two alternators had a different number of wires connected to them.

1) The alternator required a voltage sensing wire connected DIRECTLY to the battery post, and NOT to any other "equivalent" location. The voltage sensing wire is measuring tenths of a volt, and locating it, for instance, on the HEAVY battery lead where it connects to the starter would not work well. It caused the voltage output to pulse at about once/second.

2) The older alternator required an external "excitation" wire, and the new one did not. That left the installer with one "extra" wire, and I cannot remember where he put it, but it caused a problem. The type that requires an "excitation" wire, will not work without it.

I think if you understand even a little about how alternators work, you may be able to compare the two wiring diagrams and possibly determine what is wrong. In all the descriptions of problems like this that resulted from replacing one alternator with a "not quite equivalent" one, the problems were always mis-wiring. Sorry I can't be much more help.
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Old 06-23-2015, 09:32 PM   #42
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I'm fairly sure I'm close. I know the wiring is right. Now I just need to find out what's blown to keep the normal exciter route from working.
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