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Old 01-04-2021, 07:05 PM   #1
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Default Electrical charging problems, need your interpretation.

Hi all, thanks for reading. I posted this on the Chinook RV forum site but minimal response so I'm posting here too:

I went to inspect a '94 Chinook Concourse that I am considering buying. There were some red flags when I inspected the electrical charging system and I was hoping for input from forum members how to interpret these red flags.

There are 2 batteries in the unit. Both are under the hood. One is an Interstate "Dual purpose" RV/marine battery which I presume in the house battery. That is located under the hood, driver's side. Then there is a smaller (narrow profile) cheap looking "Automotive" battery, also under the hood, passenger side, which I presume is the starting battery.

When the engine is on, both these batteries get delivered ~14.1 volts. Seems like the alternator is working well. When the engine is cut, after a few minutes of running a few lights in the coach, BOTH batteries discharge to ~12.1 volts. This is red flag #1. Correct me if I'm wrong, but this tells me that these batteries are run in parallel, and that the isolator solenoid has failed in the ON position, or the solenoid is for some reason bypassed alltogether. I don't think they should both have the same voltage all the time.

Second red flag: when the unit has the generator running or is connected to shore power, both batteries have a little increase in voltage, slowly up to ~12.6. I'm under the impression that the converter should be delivering voltage at least greater than 13.0, or more. When the generator or shore power are cut, both battery voltages quickly drop back down to 12.1 or so. I interpret this that the converter is not delivering an adequate charge. Is that an incorrect interpretation?

With battery voltages at 12.1 or so with only a few interior lights on after a few minutes, maybe the furnace fan, does that indicate that these batteries are deeply discharged? The Interstate battery looks new, and they claim the "Automotive" battery is also new although to my eye it looks a little older.

One more thing to add: There is evidence that a house battery existed in the hatch behind the spare tire in the rear as there are battery cables and a "footprint" of a prior battery left on the carpet in there. It was removed for an unclear reason, and there was no voltage being delivered to those cables, but I can't remember if we tested them with the engine running. Not sure how this is relevant to the overall picture.

Anyways, trying to interpret if this electrical charging system is faulty, which I think it is, and the primary reason I didn't purchase the rig yet. Let me know your thoughts or if you have any other diagnostic questions / recommendations. Thank you.
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Old 01-05-2021, 06:28 AM   #2
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The electrical system may be faulty but all repairable. If you can’t repair it, let it go. If you have the knowledge or willingness to get the knowledge to make it work then don’t let it be a deal breaker.

First thing to do would be to bring the batteries up to 100%. That would be by specific gravity if they are flooded lead acid or 14.4 volts and two amps charging rate if AGM (I think).

That electrical system should be an easy fix or upgrade. Just don’t expect to buy it and hit the road immediately. I suspect the batteries are under charged and getting them to an honest 100% will help a lot. It is a plus you have an unused coach battery box to work with.

Just an opinion.
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Old 01-05-2021, 11:04 PM   #3
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I second the above comment, worse scenario would be new batteries, isolator and converter. BestConverter - Converters, Inverters, Electrical Supplies, Electronics is a good place to see the prices. If their price with fixes is within your budget go for it. Bade on your description it seems fix should be well within your capability.
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Old 01-06-2021, 10:19 PM   #4
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There is a lot of ambiguity here, but let me make some initial attempts at interpreting your observations:

Red flag 1: Yes, it appears the batteries are not isolated. If you disconnect them right after turning the engine off (not while running which would kill your alternator), wait 30 minutes or so, and then take the reading what do you get? If it is higher then you have some ongoing drain on the batteries. 12.1v corresponds to about a 50% SOC, so if you run the engine for a while and only end up at 12.1V you probably have damaged batteries, regardless of how new they are.

Second red flag: I think the most likely reason for not seeing a bigger voltage rise is that you have a failed converter. There are less likely but also possible causes like poor grounding or a loose connection somewhere that could also cause this condition. You could find the converter and verify that it is receiving 120v power (with a non-contact voltage detector against the input) and measure the 12v output at the converter to see if it is maintaining a charging voltage (e.g. >13v).

Battery condition: If you drain a brand new 12v battery to 0% charge a handful of times it is ruined no matter how new it still looks. So yes, seeing it at only 12.1v is certainly a warning sign. The good news is that batteries are quite cheap compared with the cost of the unit and you should just plan on replacing them immediately anyway. The bigger concern is why are they damaged? It could be poor treatment of the batteries by someone who doesn't know not to drain them too far, or it could be malfunctions in the system that are causing them to drain. The latter is more important.

Extra battery box: I see this as a bonus! You will not regret having more places to stash batteries in your rig. Hopefully the cables have just been disconnected and are ready to re-use whenever you want to expand your battery capacity.
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Old 01-10-2021, 07:30 PM   #5
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It's almost guaranteed that when you buy an older RV, both batteries need replaced. And that's a good thing, since nothing will ruin your RV camping experience like dead or dying batteries. Just factor in upgrade cost and go with lithium batteries and a new charging system. You'll be glad you did.
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Old 01-10-2021, 07:48 PM   #6
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Just to chime in...! One thing to look for is to make sure that the converter is properly configured (My Tripp-Lite 1250 has Dip Switches that needs to be set...!) for the type of Batteries to be charged. As well, I know your rig is not a Roadtrek, but the following simulator (Extremely well made...) can give you idea on how things could be connected. I have no knowledge of the Chinook but I suspect that in the end there are few similarities.
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Old 01-11-2021, 01:38 PM   #7
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Agree with all of the comments. Only way to be sure about the batteries is to disconnect them; charge them; let them sit for an hour or so and then test them using a meter that would put a load on them. Any battery store can do that for you. If you have a good price on the unit, just assume that you would be replacing all of the components mentioned, as stated before. Unless the batteries are sitting there with brand new date codes; most of us would go ahead and replace them anyway. Cheap insurance.
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Old 01-11-2021, 04:04 PM   #8
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electrical checks need to be done with known good fully charged batteries


a duff battery will skew all readings making them useless






in your position I would bring with me and connect good batteries, then start testing


that's alot of trouble but better than a guess
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Old 01-12-2021, 03:33 AM   #9
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Two batteries that need to be replaced and that will cost about $300 in total and so not a big deal. Worst case the alternator or relay may need to be replaced and a rebuilt alternator is not terrible expensive either.
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