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Old 12-18-2021, 08:37 PM   #1
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Brand: Thor Motor Coach
Model: Vegas 25.6
State: Maryland
Posts: 9
THOR #15350
dead 12V coach and chassis

I have a 2018 Thor Vegas 25.6 (the one with the big slide). It's broken in enough that I thought we had all the kinks worked out of it (other than needing more mouse-proofing).

We last used it in early October, no problems. I then had it plugged in for a month to have 120V to run an ultrasonic rodent repeller, winterized it, and left it unplugged for 3 weeks, "use" switch off.

I then discovered none of the 12V systems are working. Both coach and chassis. It won't crank, absolutely zero sign of power from the chassis, and I can't jump it. Generator won't crank. Coach power still works off shore. Control panel registers full charge on the coach batteries, and 1.6V on the chassis (which I think means it can't detect the chassis battery). I started pulling the chassis battery, put a charger on it, and the charger says it's fully charged.

The trip circuit next to the coach batteries is fine. As is a 100A trip circuit next to the chassis battery. 15A fuse on the BIRD is fine.

What could be causing this?

Or can anyone in the Maryland Baltimore-DC area recommend someone who does on-site RV repairs?

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Old 12-18-2021, 09:02 PM   #2
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THOR #13058
Quote:
Originally Posted by Terence View Post
I have a 2018 Thor Vegas 25.6 (the one with the big slide). It's broken in enough that I thought we had all the kinks worked out of it (other than needing more mouse-proofing).

We last used it in early October, no problems. I then had it plugged in for a month to have 120V to run an ultrasonic rodent repeller, winterized it, and left it unplugged for 3 weeks, "use" switch off.

I then discovered none of the 12V systems are working. Both coach and chassis. It won't crank, absolutely zero sign of power from the chassis, and I can't jump it. Generator won't crank. Coach power still works off shore. Control panel registers full charge on the coach batteries, and 1.6V on the chassis (which I think means it can't detect the chassis battery). I started pulling the chassis battery, put a charger on it, and the charger says it's fully charged.

The trip circuit next to the coach batteries is fine. As is a 100A trip circuit next to the chassis battery. 15A fuse on the BIRD is fine.

What could be causing this?

Or can anyone in the Maryland Baltimore-DC area recommend someone who does on-site RV repairs?
You did nice job of laying it out, but one thing that stood out that you missed is to tell what voltage readings did you get direct from both batteries using a voltmeter?

Also, when you say power was restored on house batteries when shore power is supplied, are you confirming house batteries are being charged? Have you waited long enough for house batteries to get fully charged to use emergency start; for chassis?
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Old 12-18-2021, 10:01 PM   #3
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THOR #13362
Vegas/Axis have a “parasitic” draw, even when in the STORE position.
That is, the Co2 sensor, along with the Dash Radio head unit is always drawing power.
Suggest you get a BatteryDisconnect switch on the Negative side of where your battery bank enters the coach.

That way nothing will be on while in storage.

Here’s a couple that I have used…

https://smile.amazon.com/CZC-AUTO-Di...NsaWNrPXRydWU=

https://smile.amazon.com/Ampper-Batt...s%2C160&sr=8-4
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Old 12-18-2021, 10:09 PM   #4
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THOR #13932
There are two, not one, breakers next to the coach batteries.
On my 2018, one is mounted on top of the other making it really hard to see.

Find that second flag breaker.
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Old 12-18-2021, 10:24 PM   #5
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THOR #15350
My voltmeter isn't working, so I'll need to go out and get a new one to get real readings.

When plugged into shore power, the Thor control panel registers that the coach batteries are there and it's sending a charging voltage, but I don't know what charge they have since the panel won't currently work without shore power. My charger reports what looks like a full charge on the chassis battery, but it's not a digital readout so I don't have a precise number from it. It's certainly enough that I should get life from the dashboard and some effort to crank.

I've had the unit parked for many months with the "use" switch off without noticeable drain on the coach batteries, and it's always started right up. Not sure why others have more problems with parasitic loss than I do. And would that affect starting off the chassis battery (including not jumping)?

> On my 2018, one is mounted on top of the other making it really hard to see.

Am I crazy? I don't see a 2nd one:
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There is a 2nd one up by the chassis battery which also isn't tripped. Do they just randomly put these anywhere they please when building a coach? Or is there another one by the coach batteries that I'm completely missing?
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Old 12-18-2021, 10:35 PM   #6
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THOR #13362
On mine, theres a 100 amp with a push button switch
And
A 50 amp without a switch (see photo below)

Both fuses, I believe, have flags which indicate they are off .

But to completely disengage all power, there must be a special battery disconnect installed.
That is, dis-connecting negative cables from both batteries.

(Im sure someone will correct me if Im wrong)
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Old 12-18-2021, 10:59 PM   #7
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THOR #13058
Quote:
Originally Posted by Terence View Post
My voltmeter isn't working, so I'll need to go out and get a new one to get real readings.

I've had the unit parked for many months with the "use" switch off without noticeable drain on the coach batteries, and it's always started right up. Not sure why others have more problems with parasitic loss than I do. And would that affect starting off the chassis battery (including not jumping)?
I read that a lot too, so much so I bought my RV expecting the batteries to drain. 1st thing I installed was chassis disconnect switch. two plus years and I have never needed it, I can go months (but I never need to) with nothing on and it starts right up.

Now if the House battery is in Use mode, and everything is off, I do have some drain like power for cable and power to things like my sound bar, roku, and carbon monoxide detector etc. But I can go weeks with that stuff on.
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Old 12-18-2021, 11:00 PM   #8
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THOR #7035
Quote:
Originally Posted by Terence View Post
I have a 2018 Thor Vegas 25.6 (the one with the big slide). It's broken in enough that I thought we had all the kinks worked out of it (other than needing more mouse-proofing).

We last used it in early October, no problems. I then had it plugged in for a month to have 120V to run an ultrasonic rodent repeller, winterized it, and left it unplugged for 3 weeks, "use" switch off.

I then discovered none of the 12V systems are working. Both coach and chassis. It won't crank, absolutely zero sign of power from the chassis, and I can't jump it. Generator won't crank. Coach power still works off shore. Control panel registers full charge on the coach batteries, and 1.6V on the chassis (which I think means it can't detect the chassis battery). I started pulling the chassis battery, put a charger on it, and the charger says it's fully charged.

The trip circuit next to the coach batteries is fine. As is a 100A trip circuit next to the chassis battery. 15A fuse on the BIRD is fine.

What could be causing this?

Or can anyone in the Maryland Baltimore-DC area recommend someone who does on-site RV repairs?
I'm not familiar with a control panel that indicates both house and chassis battery status, but if you are plugged into SP it reads the voltage from the converter, not the house batteries. The fact that the chassis battery still reads dead tells me not charge is getting to the house batteries, and consequently, not the chassis battery either.

If the house batteries are dead you can not change the USE/STORE switch to use - they must be charged externally first.

The 100 amp DC breaker goes to the generator; there is also a 50 amp DC breaker that goes to the house DC buss through the USE/STORE latching relay. On a Class C it can be very hard to find, but it is there - but It is probably not your problem here.
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Old 12-18-2021, 11:04 PM   #9
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THOR #15350
wow, tricky breaker. The 2nd 50A one is mounted above the 100A on mine, and was tucked in behind a wire so I didn't see it. It's fine, not tripped.

I'll get a new voltmeter tomorrow and check all 3 batteries.
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Old 12-18-2021, 11:07 PM   #10
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THOR #13932
Quote:
Originally Posted by Terence View Post
wow, tricky breaker. The 2nd 50A one is mounted above the 100A on mine, and was tucked in behind a wire so I didn't see it. It's fine, not tripped.

I'll get a new voltmeter tomorrow and check all 3 batteries.
Trip it and reset it.
Do both breakers.
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Old 12-18-2021, 11:52 PM   #11
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Quote:
Originally Posted by 16ACE27 View Post
I'm not familiar with a control panel that indicates both house and chassis battery status, but if you are plugged into SP it reads the voltage from the converter, not the house batteries. The fact that the chassis battery still reads dead tells me not charge is getting to the house batteries, and consequently, not the chassis battery either.
My panel is the touch panel that runs everything including the lights. It has separate readouts for both coach and chassis. Now that I think more about it, I've only paid any attention to the readouts when disconnected from shore power, when it properly reads the chassis battery voltage. But maybe it's expected to not read the chassis battery at all when on shore power. So that might not be informative of anything,

Quote:
Originally Posted by ducksface View Post
Trip it and reset it.
Do both breakers.
How do you get the 50A one to trip? Mine lacks a test button. It looks like this pic:
https://www.thorforums.com/forums/sh...42&postcount=5
The camper is clearly winning when I can't figure out how to trip a simple breaker!

I guess simplest possibility is I forgot to hit the use switch and drained the coach batteries to nil, and maybe that's set off some safeguard that also affects the chassis power system. I'll know more tomorrow with a working voltmeter, or I'll pull the coach batteries and see how my charger thinks they're doing.
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Old 12-19-2021, 08:23 PM   #12
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THOR #15350
Looks like my charger was deceiving me, and all three batteries are indeed very dead (reading ~2V, I went and checked the battery on my car to make sure the meter was working right). Still an unknown as to why it happened - even leaving the "use" switch on shouldn't have drained the engine battery.

It looks like I've convinced my charger to try charging at least one of the coach batteries. It might have been misreading because they're cold. Hopefully I can get enough voltage into them to see if it'll crank and solve my problem, and then see if I can get a full charge into them. I may need to pick up a charger with a desulfation mode.

I'll post later how things turn out. Fingers crossed!
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Old 12-19-2021, 09:05 PM   #13
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THOR #13058
Quote:
Originally Posted by Terence View Post
Looks like my charger was deceiving me, and all three batteries are indeed very dead (reading ~2V, I went and checked the battery on my car to make sure the meter was working right). Still an unknown as to why it happened - even leaving the "use" switch on shouldn't have drained the engine battery.

It looks like I've convinced my charger to try charging at least one of the coach batteries. It might have been misreading because they're cold. Hopefully I can get enough voltage into them to see if it'll crank and solve my problem, and then see if I can get a full charge into them. I may need to pick up a charger with a desulfation mode.

I'll post later how things turn out. Fingers crossed!
Now that you have voltmeter and know all batteries dead with low voltage.

Turn on shore power, go tell us the EXACT voltage readings on all of the batteries.
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Old 12-19-2021, 10:09 PM   #14
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Quote:
Originally Posted by dkoldman View Post
I read that a lot too, so much so I bought my RV expecting the batteries to drain. 1st thing I installed was chassis disconnect switch. two plus years and I have never needed it, I can go months (but I never need to) with nothing on and it starts right up.

Now if the House battery is in Use mode, and everything is off, I do have some drain like power for cable and power to things like my sound bar, roku, and carbon monoxide detector etc. But I can go weeks with that stuff on.

Same here if not plugged on and using nothing chassis and coach not bad
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Old 12-19-2021, 10:36 PM   #15
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THOR #7035
Quote:
Originally Posted by Terence View Post
Looks like my charger was deceiving me, and all three batteries are indeed very dead (reading ~2V, I went and checked the battery on my car to make sure the meter was working right). Still an unknown as to why it happened - even leaving the "use" switch on shouldn't have drained the engine battery.

It looks like I've convinced my charger to try charging at least one of the coach batteries. It might have been misreading because they're cold. Hopefully I can get enough voltage into them to see if it'll crank and solve my problem, and then see if I can get a full charge into them. I may need to pick up a charger with a desulfation mode.

I'll post later how things turn out. Fingers crossed!
All your batteries are in the coach. To prevent confusion the engine battery is called the CHASSIS battery and the other batteries are called the HOUSE batteries.
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Old 12-20-2021, 02:07 AM   #16
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I may have missed it, but I didn't read what your battery maintenance plan is. Leaving lead acid batteries sit idle in cold weather for several weeks at a time is not ideal.

I would urge you to at minimum connect a smart battery maintainer (trickle charger) to BOTH house and chassis batteries. That will keep them topped off and prevent unnecessary sulfation.

I know some people leave theirs sit for extended periods, then use the generator exercise routine to charge the batteries. If you let them discharge, you are using up your limited charge/discharge cycles... without getting any benefit. Since it sounds like you have an accessible power source, this would be a cost effective solution... even with a parasitic drain.

But... you're going to have to remedy your current dead battery situation first.
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Old 12-22-2021, 08:07 PM   #17
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THOR #15350
Update: I was able to charge all three batteries and restore 12V power and start the engine. The coach/house batteries look like they charged up to ~12.6 V (after sitting for a day with no load). They might not yet be fully charged. So no obvious signs of major sulfation loss, but we'll see. The engine battery needs to sit for longer to see what its final voltage winds up at. Then I'll have to decide whether I want to replace the batteries now or wait and see.

I still have the outstanding question of why they went dead. I have not previously had the parasitic loss problems that some others report. I've had the unit for 2.5 years, and haven't had problems before while sitting for much longer than this was (4+ months). That includes checking for voltage drop on the panel, with no obvious sign of the batteries draining. Plus I wouldn't expect all three batteries to be drained.

If I had accidentally left the use switch "on", that definitely would have drained the coach/house batteries down. I thought the chassis battery was still isolated with the use switch "on". Is that not true, or can it get crossed in if the coach/house batteries go dead?

I need to figure out if something changed/broke, resulting in the drain, or I just did something stupid. So I think my next step is trying to measure for parasitic loss on both 12V systems.
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Old 12-29-2021, 07:28 PM   #18
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THOR #14429
Terrence, if u still want a local repair shop i have used Atel Bus and RV in Beltsville, MD. Ask for Brian Connoly
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