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Old 12-25-2014, 09:39 AM   #1
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Chassis battery problem

I'm having a problem I can't quite figure out on an 03 revolution.
Coming back from a trip last week the low battery voltage warning came on. The dash voltmeter was slightly below 13v. I could hit the aux batt button and voltage would come up and clear the warning.
I hooked up to shore power when I got home and did done searching on here.
I disconnected the batteries and both read 12.7v over a period of several days. This morning I hooked them back up and started the engine with shore power unhooked. They read 12.2v.....never seeing any additional voltage from the alternator. I turned the engine off and they returned to 12.7 v.
Do I have an alternator problem, battery problem or charging system problem?
Will the generator still try to charge the batteries with the engine running or is it locked out to rely on the alternator? Is the alternator tied directly to the batteries or does it go through an isolator that could be bad?
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Old 12-25-2014, 10:17 AM   #2
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It would help us help you if you identify what type of motorhome and chassis you have.

Did your house and chassis battery systems both charge when on alternator, generator, and shore connection before this started happening? Only having 12.2 v with engine running points to no alternator power. Worst case: new alternator, best case: dirty connection.
I'd start with looking for dirty connections, bad ground, etc. Proceed from there. With a mutimeter check voltages at each battery group after resting and hour or two, then hooked to shore power, hooked to generator, engine running. Try to isolate where the connection is missing.
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Old 12-25-2014, 10:24 AM   #3
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Welcome! , you did not say how old the batteries are? And age really does not matter, as even a new battery can develop internal problems just as a older battery can. The first thing I would do is "load test" the batteries.........and know if they are up to snuff........good condition, and then go from there. Now, clean all connection's putting them/new back in.......
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Old 12-25-2014, 10:34 AM   #4
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First I would like to wish you a Merry Christmas. I am not familiar with your brand of coach. My last 3 were Winnebago coaches so I will try and answer your questions as it relates to what I am familiar with. My first guess is you have an alternator problem. To your question about your aux generator charging your batteries, I believe the aux generator should charge your coach batteries just as when you are plugged into 120V power. On my rig the coach charger does not charge the chassis battery. If my alternator quit charging I would have to jump the + post on the chassis battery to the + post on the coach battery to feed power to the chassis battery. I would have enough battery power to get me into a repair facility. The fact that when you activated your aux battery button and the voltage on your chassis would raise to turn off the warning leads me to believe your coach batteries are holding power and are not your problem. When you disconnected your batteries for several days and they still had 12.7 volts that tells me they are not likely your problem either.

Sorry I can't answer the rest of your questions. When you have located your problem and get it repaired post back on this thread what solved your problem as we all learn from each other.

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Old 12-25-2014, 11:12 AM   #5
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You fried a diode in your alternator. Yo have a six of them and when one fails you will loose around 2 volts.To check the diodes just use a multimeter on ohms and check them.one way you will get a reading and the other will show open normally they short out.
my 2 cents
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Old 12-25-2014, 11:15 AM   #6
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Revosnzrs,


I had similar problem a few months ago. If you can get to it, check the voltage coming off of the alternator. Bet it's low, or none. When you hit the aux batt switch the volt meter on dash is reading the combined voltage from both sets of batteries. My coach is wired to charge both sets of batteries when on shore power so when I got to destination and charged up the batteries my voltage showed low 13s. as I would drive next day it would slowly decline to low 12s after about 5 or 6 hrs. I took the alternator off and had it totally rebuilt for about $200.00. Still no juice. Found a resetting breaker for my sensing wire from the alternator was faulty. $3.99 part and it jumped to over 14V.
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Old 12-25-2014, 11:16 AM   #7
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Thanks for the responses. I check all of the things you all have suggested.

How do I check the diodes?
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Old 12-25-2014, 11:18 AM   #8
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Quote:
Originally Posted by Johndale View Post
You fried a diode in your alternator. Yo have a six of them and when one fails you will loose around 2 volts.To check the diodes just use a multimeter on ohms and check them.one way you will get a reading and the other will show open normally they short out.
my 2 cents
Wow, what diagnosis specificity! From the info given, how did you eliminate all the other possibilities?? The rest of us are still at the information gathering step and you were able to jump to a bad diode so quickly! Which of the six is it?
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Old 12-25-2014, 11:21 AM   #9
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the diodes are on the back of the alternator a bank of 3 on each side of the back case. They are normally round and like I said above use a multimeter and flip the leads to check them. peen on one and closed when you flip the leads
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Old 12-25-2014, 11:24 AM   #10
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https://video.search.yahoo.com/video...t=mozilla&tt=b
hope this works for you
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Old 12-25-2014, 11:25 AM   #11
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Might add that when the alternator was rebuit I too had burned up diodes in mine. Take the alternator off and take it to an alternator shop and have it tested is the easiest way
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Old 12-25-2014, 11:26 AM   #12
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Old 12-26-2014, 10:23 AM   #13
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Ok. I tried to look into what has been suggested.
The coach is on a freightliner chassis. The batteries are around two years old-from SAMs.
Here is what I have found so far.
It was hooked up to shore power overnight. Voltage at the chassis batteries was a little over 14v, so they were definitely being charged. I unhooked and voltage came down to just under 13v. Started the generator and again they came up to 14+V. I started the coach engine with the gen running and they dropped to 12.2V which told me that the gen charging is apparently locked out with the cummins engine running. Next I pulled up the floor in the closet to check the voltage at the alternator and got 0V.
I want to make sure I'm not missing something before I attempt to pull out the alternator (I have stitches in my back from surgery last week and am trying not to stretch too much).

Should I see 0V at the alternator or should I at least read battery voltage? I want to make sure it's not just me getting a bad ground on my neg lead to the DMM.

Secondly, can I check the diodes and get an accurate reading without unhooking the wiring to the alternator? And does that matter if I'm reading 0V? I'm still going to have to pull the whole thing and have it rebuilt or buy a new one right?
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Old 12-26-2014, 10:28 AM   #14
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Likely alternator bad but zero volts not correct so maybe broken connection.

Output from alternator goes to isolator and if that is open no battery voltsge at alternator.

There may be a control wire from ign to turn it on while running.

You should have fat wire for output and a small wire for exciter or control.

Search for wiring diagram as alt may be fine
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