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Old 06-13-2021, 10:00 PM   #1
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Brand: Thor Motor Coach
State: North Dakota
Posts: 4
THOR #23816
Electrical Problems

Hi all,


I purchased a 2016 Thor Majestic 23a in December and all was well until this week. From Dec-May I was hooked up to shore power 24/7 and everything worked. I recently took a cross country trip and didn't have any problems. The RV was unplugged from shore power and in storage for 2 weeks and now the chassis battery is completely dead. I installed a new radio before the trip and assumed it put some parasitic drain on the battery. It is a previous rental unit and doesn't have a storage/isolate switch, but it does have an emergency start button.

I used this and the RV started. After starting the RV I used a volt meter and the chassis battery was at 18V! I turned the RV off and sure enough the house battery is at 18V.

My initial though is it is a bad converter (WFCO 8955) overcharging the house battery. After googling I found info stating a bad battery can cause a converter to overcharge a battery. To add to my confusion the chassis battery is out of the RV and the emergency start switch is not depressed, but the door lights, dash lights, and radio are working.

Is this normal? When the dead chassis battery was connected I had no power to the dash lights or door locks. I thought there was a relay or solenoid that connects the house battery to the chassis battery when pressed.

The house battery is AGM and the chassis battery is a Motorcraft, both have dates from 2020. I had the Motorcraft battery tested and its dead and won't accept a charge. I know I have to replace the chassis battery, but any tips on troubleshooting or normal charging operation would be greatly appreciated!

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Old 06-14-2021, 12:08 AM   #2
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Brand: Thor Motor Coach
Model: Citation
State: Texas
Posts: 760
THOR #8139
We keep a battery maintainer on our chassis battery, shore power/generator don't charge the chassis battery our SOB class A did
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Old 06-14-2021, 12:28 AM   #3
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Brand: Still Looking
Model: Tiffin Wayfarer 24 BW
State: New York
Posts: 21,733
THOR #8860
I use a 40 Watt solar panel to keep my chassis battery well-juiced.
The coach batteries get a drink from their shorepower hook-up.
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Old 06-14-2021, 03:03 AM   #4
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Brand: Thor Motor Coach
State: North Dakota
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THOR #23816
I went back to the RV today and the dash lights, radio, and door locks weren't working. This is what I would expect without a chassis battery. This is my first RV but I don't understand how these things got power without a chassis battery installed earlier. I assume from a relay? Is there a way to test if this was normal function or a bad relay?

Having the house battery at 18V is it more likely a converter issue or did the alternator overcharge the battery since the chassis battery was bad?


Thanks!
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Old 06-14-2021, 12:29 PM   #5
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Brand: Thor Motor Coach
State: Missouri
Posts: 1,817
THOR #6903
Very difficult to get to 18v DC

High voltage for an extended time will fry electronics and some lamps

You should have a relay/solenoid connection between chassis/house

If you have EMS it should have shut down power
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Old 06-15-2021, 01:48 AM   #6
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Brand: Thor Motor Coach
State: North Dakota
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THOR #23816
what is the "norm" for an EMS? I'm looking at upgrading the converter to a Progressive Dynamics but see no mention of an EMS. I'd like the peace of mind to prevent this from happening again....and possibly upgrading to Lithium if the battery is fried/when its time to replace the house battery.
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Old 06-20-2021, 03:21 AM   #7
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Brand: Thor Motor Coach
State: North Dakota
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THOR #23816
Update:

Turns out my voltmeter battery was dead and was wayyyy off. Recharged the the chassis battery and everything appears to be operating correctly (after replacing my voltmeter batteries). Thanks for the help!
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