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Old 08-15-2022, 11:19 AM   #1
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Brand: Thor Motor Coach
Model: Daybreak 26'
State: Illinois
Posts: 13
THOR #19020
Coach Battery Drain

I have a Thor DB26, 2020. Ford frame, gasoline. Bought brand new in 2019 and currently has less than 8k miles.

Over the last few months I have had an unexplained drain on my coach battery. When unplugged from shore power, with coach master power switch in off position, the battery will lose voltage at a fairly steady rate. Approximately 1/10 of a volt every couple of hours.

The battery is an Interstate 12 Volt deep cycle. I took it in to the local dealer, he tested it and replaced it with a brand hew model (the first was less than a year old). Brand new battery did exactly the same thing.

I am assuming either something has been accidentally activated that shouldn't have been or somewhere there is a short. Any suggestions as to where to look would be appreciated.

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Old 08-15-2022, 12:43 PM   #2
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Model: Axis 24.1
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THOR #20289
A tenth of a volt drop every couple of hours is very roughly 10% of your battery capacity. Your battery is probably a Group 27 so 10% is probably 7 amp hours. That is a huge "parasitic load", so something is going on.

Beg, borrow or buy a DC clamp on ammeter. Klein Tools is a decent brand and they are $90 on Amazon. See- https://www.amazon.com/Klein-Tools-C...96&sr=8-3&th=1 Every DIY should have one.

Then measure the current from each wire attached to the positive terminal of the battery. One should be high. Then see where that wire goes and trace the current down. I'll bet it is a relay like the starter solenoid on the generator that has gotten stuck and draws current continuously.

Until you find it, disconnect the negative cable to the battery which will shut down all circuits.

David
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Old 08-15-2022, 01:59 PM   #3
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THOR #16471
Most RVers have a multimeter that will measure Amps... (up to 10A) so in a pinch, like the OPs drain, just use it for a quick test. A clamp-on is nice for higher current, but parasitic loads may not be accurate.





Place meter to Amps (in this image ONLY DC is available!)
Place RED lead to 10A connection (Note the note that it is UNFUSED!)
Ensure all known DC load is "OFF" and as David mentioned, remove 'neg' battery post connection and place meter in series with the post and connector.
With a digital multimeter, polarity is not important, but in any case the black lead would go on the neg post and the red lead to the connector.

If it is a drain, the meter will indicate "-" in front of the reading...

Do NOT measure charging current as the meter will not like anything greater than 10 amps. Or do not operate anything as it could be greater than 10 amps. Do this only for suspect parasitic drains. Can be done on chassis battery too.

**Remember this is UNFUSED, so be careful**


When done, REMEMBER to return the red lead back to the VΩmA terminal before measuring voltage. I have made that mistake too many times. :-/
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Old 08-15-2022, 02:23 PM   #4
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THOR #5248
Do you have an inverter? If it on, even with no load it will use power. And it doesn’t go through the use, store relay
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Old 08-15-2022, 02:56 PM   #5
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Originally Posted by Trkyte@msn.com View Post
Do you have an inverter? If it on, even with no load it will use power. And it doesn’t go through the use, store relay
Good suggestion! He has no OEM inverter but maybe an aftermarket install?
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Old 08-15-2022, 03:32 PM   #6
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THOR #19020
No after market inverter has been installed.
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Old 08-15-2022, 04:07 PM   #7
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THOR #19020
More information, maybe

I just got a call from my wife who was storing some stuff in the RV. She told me that she noticed a sound which sounded like a small fan running. It appeared to be coming from behind the circuit breaker box. I had her double check the coach disconnect switch and she verified that it was in the "off" position. No shore power connected.
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Old 08-15-2022, 05:56 PM   #8
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Originally Posted by Dcn Steve View Post
I just got a call from my wife who was storing some stuff in the RV. She told me that she noticed a sound which sounded like a small fan running. It appeared to be coming from behind the circuit breaker box. I had her double check the coach disconnect switch and she verified that it was in the "off" position. No shore power connected.
Do you have the manual battery disconnect like this:



or the remote switch that controls a latching relay that look like this?

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Old 08-15-2022, 07:14 PM   #9
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THOR #19020
Quote:
Originally Posted by 16ACE27 View Post
Do you have the manual battery disconnect like this:



or the remote switch that controls a latching relay that look like this?

The first choice is similar to the manual disconnect switch in my unit. Rotates between On and Off. It is a different brand. I will take a picture when I get home today. There is also a solar charge controller next to the disconnect switch, however I do not have any solar panels installed.
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Old 08-15-2022, 07:34 PM   #10
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Originally Posted by Dcn Steve View Post
The first choice is similar to the manual disconnect switch in my unit. Rotates between On and Off. It is a different brand. I will take a picture when I get home today. There is also a solar charge controller next to the disconnect switch, however I do not have any solar panels installed.
This is the solar controller.

[IMG]C:\Users\seischens\OneDrive\Desktop\SolarControlle r[/IMG]
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Old 08-15-2022, 07:40 PM   #11
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THOR #20110
We had a similar problem with a 2018 Thor Windsport 35M, which we bought used from a dealer. Something (never specifically identified) was drawing current. We installed the rotating battery cut off switch, similar to the one pictured. That seemed to help the problem. We are not DIY-ers. We never did any sophisticated voltage drain investigation. Service people did find several electrical issues and incorrect wiring connections, apparently from the factory. Tough to diagnose, unless someone is very skilled. Over time we wound up replacing the transfer switch, inverter, and batteries. Throw enough money at a problem, and if you're lucky you can fix it.
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Old 08-18-2022, 11:48 AM   #12
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THOR #19020
Possible Solution

I may have found the solution.
In trying to track down the mysterious intermittent fan sound, I happened to notice that the solar panel charger control unit LED panel had a black dot "on" next to a battery icon. I pressed the selector button until that black dot, and all others, were gone. The fan noise stopped. I charged the batter to full capacity and it has held the charge now for three days.

I am not sure how the setting got changed, although any one of six grandkids may have had something to do with it. I have no solar panels nor an inverter installed. All I can assume is that there is a thermal activated switch on a cooling fan in that circuit somewhere that would be activated with the very high temperatures we have been having lately.

In any case, I will let you know if this turns out to not be the solution. It is a good one to put in the random electrical information for future questions and solutions.
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Old 08-18-2022, 01:19 PM   #13
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THOR #7035
Quote:
Originally Posted by Dcn Steve View Post
I may have found the solution.
In trying to track down the mysterious intermittent fan sound, I happened to notice that the solar panel charger control unit LED panel had a black dot "on" next to a battery icon. I pressed the selector button until that black dot, and all others, were gone. The fan noise stopped. I charged the batter to full capacity and it has held the charge now for three days.

I am not sure how the setting got changed, although any one of six grandkids may have had something to do with it. I have no solar panels nor an inverter installed. All I can assume is that there is a thermal activated switch on a cooling fan in that circuit somewhere that would be activated with the very high temperatures we have been having lately.

In any case, I will let you know if this turns out to not be the solution. It is a good one to put in the random electrical information for future questions and solutions.
Good job!

That was probably it.
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Old 08-20-2022, 07:57 PM   #14
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Model: Aria 3901
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THOR #2538
I had the exact same this happening on my Challenger. I could never find why it did that, and finally just disconnected the positive lead off the house batteries and tripped the 100-amp circuit breaker to ensure no current flow. I suspected my convertor wasn't disconnecting by throwing the battery disconnect switch to store (vice use) like it should have.
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Old 08-21-2022, 01:58 PM   #15
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THOR #6722
I had my RV mechanic put a knife switch on the coach batteries. Prevents draws it's worked out perfectly.
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