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Old 02-01-2022, 02:21 PM   #1
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Coach is draining chassis battery when boondocking

Hello,


I have a 2018 Thor Hurricane motorhome. I have an issue where the coach is draining the chassis battery (as well as the house batteries) when boondocking (or parked with something left on). The house batteries charge fine when driving or with the generator. And the generator is not charging the chassis battery. If the solenoid that allows the house batteries to charge from the engine alternator was stuck closed, then I would assume that running the generator would also charge the chassis battery, which it is not.


I recently took the family to a resort with an indoor waterpark for a long weekend. The weather got down to 25F, so the furnace was left on to keep things from freezing. When I went out the next morning, both the house batteries and the chassis battery were dead. I got someone to give me a jump on the house batteries, and started the generator. It ran for 1.5 hours to charge up the house batteries, but did nothing for the chassis battery (which I understand it is not supposed to do). But, it is also not supposed to drain the chassis battery. I could just replace the solenoid, but to me it seems if it is stuck closed allowing the coach to drain the chassis battery, then it should also allow current to go backwards charging the chassis battery.


Wondering if anyone has any ideas? Thanks!
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Old 02-01-2022, 10:30 PM   #2
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Put a meter on both sets of batteries I would bet they are the same voltage.
I would check to see if anything changes by removing grout on switch temporarily


Quote:
Originally Posted by edwardbuck View Post
Hello,


I have a 2018 Thor Hurricane motorhome. I have an issue where the coach is draining the chassis battery (as well as the house batteries) when boondocking (or parked with something left on). The house batteries charge fine when driving or with the generator. And the generator is not charging the chassis battery. If the solenoid that allows the house batteries to charge from the engine alternator was stuck closed, then I would assume that running the generator would also charge the chassis battery, which it is not.


I recently took the family to a resort with an indoor waterpark for a long weekend. The weather got down to 25F, so the furnace was left on to keep things from freezing. When I went out the next morning, both the house batteries and the chassis battery were dead. I got someone to give me a jump on the house batteries, and started the generator. It ran for 1.5 hours to charge up the house batteries, but did nothing for the chassis battery (which I understand it is not supposed to do). But, it is also not supposed to drain the chassis battery. I could just replace the solenoid, but to me it seems if it is stuck closed allowing the coach to drain the chassis battery, then it should also allow current to go backwards charging the chassis battery.


Wondering if anyone has any ideas? Thanks!
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Old 02-02-2022, 05:15 AM   #3
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Coaches are wired many many different ways with many many different equipment setups. That being said...in my coach the generator wont charge the chassis batteries until the house batteries are above a certain voltage (14.0 or so can't really remember). So if all my batteries are dead it would take 8-10 hours of generator charging the house batts before the chassis batts would start charging. Did you wait that long to see if they started charging?

To describe how my coach works a bit further. When all my batts are fully charged the house and chassis batts are connected via a large solenoid. When all the batts drain down to 12.6 the chassis batts are disconnected from the whole system to keep them from also draining. I'm guessing if there was a problem with my isolator solenoid staying closed and causing all of the batts to drain down to nothing...when the voltage got down to a certain level the isolator may have gotten below a threshold to hold it closed, and it relaxed...or the retract spring finally was able to break the contact. So now the batteries would be separated again and the generator charging would be dedicated to the house batts until almost fully charged. Which would be many many hours later especially if lead acid house batts.

And on my coach the cable that comes from the engine alternator comes from the voltage regulator which would normally only be energized when the engine is running. I would doubt (dont know for sure) there is any physical connection between the house battery cable and the chassis battery cable at the regulator. So with the engine off there should be no connection at the regulator between the 2 systems.

That's all I have to add.
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Old 02-02-2022, 05:18 AM   #4
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Don't know your coach specifically, but I believe it has some type of voltage monitor that controls a solenoid that connects and disconnects the house and coach batteries based on input voltage from alternator/converter. On my last 2 Thor coaches the monitor was a small black box in the battery compartment that sends +12 volts, when appropriate, to the isolation solenoid. The solenoid was also located in the battery compartment.



If you can locate the isolation solenoid, put a meter across the solenoid (coil) connection from the monitor and ground. Check voltage with the coach plugged in only, then with generator running only, then the engine running only. In all 3 cases you should have +12 volts DC on the coil contacts on the solenoid. Even if you are not plugged in or running engine/generator, you may have voltage from the monitor to the solenoid for a while, several minutes, if the house bank or engine batteries are fully charged. This voltage will go away if and when the batteries charge dissipates below the isolation cutoff voltage



If the voltage readings are correct, check the solenoid to see if it is passing voltage , (making/breaking contact) between the main solenoid terminals.


If the voltage is not present at the solenoid coil terminals in one of the tests then check the individual inputs to the voltage monitor. The inputs should be labeled or shown on the monitor, if not you can find here or on line once you identify the brand and type monitor you have. Probably the brand is Intellitec. Something like this:


https://www.amazon.com/Intellitec-00...ps%2C57&sr=8-1


Coach Battery terminal should be 14+ volts when generator on or plugged in if converter is working properly.


Ignition should be 14+ volts after a few seconds of the engine running.


If the input voltages are correct and the output voltages are incorrect, then the module may be bad.


If the inputs are not correct, check grounding and the intended source of voltage, (converter/ignition source)


Make sure battery switch (salesman switch) is in "USE" position, all breakers in battery compartment are reset or not tripped.

Here is info from Intellitec regarding thier typical Gas Bird:


https://intellitec.com/wp-content/up...-01000-100.pdf


Good luck, let us know what you find.
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Old 02-02-2022, 05:47 AM   #5
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You haven't said how old or the battery size and condition, the temperature but it's really possible they gave all they had and died. It's possible the chassis batteries are also shot. Like the other poster said, you need to check voltage on both sets.
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Old 02-02-2022, 07:03 AM   #6
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1.5 hours of genset time wasn't enough to charge your house batteries much less reach the threshold of switching to chassis battery charge, if that is even a feature with your RV. Might be a useful exercise to plug into shore power and watch your batteries over an extended period to understand how it's working, then from there decide if it's operating correctly and if there's anything to be done as far as chassis battery charging.

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Old 02-02-2022, 09:33 AM   #7
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Do you have a Precision Circuits BIM 160, which Thor typically installs on their MHs. My 2021 Axis has one. It is typically installed under the hood, but maybe in the battery compartment as well.

If you have one, it may be bad. With no shore power connected and the chassis engine off but well charged up after running for a while, and with some lights on to put a load on the batteries, check the voltage of the coach battery and the chassis battery. if they are the same, the BIM is probably bad. Let it run that way for a few hours and check again. The coach battery voltage has probably dropped a little. If the chassis battery has dropped to the same voltage, then the BIM is most certainly bad.

David

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Old 02-02-2022, 08:45 PM   #8
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Quote:
Originally Posted by DavidEM View Post
Do you have a Precision Circuits BIM 160, which Thor typically installs on their MHs. My 2021 Axis has one. It is typically installed under the hood, but maybe in the battery compartment as well.

If you have one, it may be bad. With no shore power connected and the chassis engine off but well charged up after running for a while, and with some lights on to put a load on the batteries, check the voltage of the coach battery and the chassis battery. if they are the same, the BIM is probably bad. Let it run that way for a few hours and check again. The coach battery voltage has probably dropped a little. If the chassis battery has dropped to the same voltage, then the BIM is most certainly bad.

David

David
Or, in many cases documented on Thorforums.com, the BIM is wired incorrectly. I had the same issue and after looking at Judges posts on this, I switched the wires around and it fixed the problem.
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Old 02-03-2022, 11:54 AM   #9
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I'll check the voltages today

Hello,


Thanks for the ideas. I've been running nonstop since I posted Tuesday. I'll have some time to check the voltages and wiring this afternoon.


The house batteries are 3 lead acid deep cycle 12v purchased Feb 2021. The chassis battery is probably original with the coach (2017/2018). I've thought about replacing it, but want to get this resolved before I do.


I'll post what find out.
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Old 02-03-2022, 12:24 PM   #10
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Some battery combiner systems such as the BIRD will only read about 3-4v dc once the solenoid is engaged, this is enough to keep it engaged and saves power.
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Old 02-03-2022, 02:02 PM   #11
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I think your start battery is dead, just get it tested. Also, maybe I am alone in this idea but I always turn my chassis off if I don't plan on starting the coach. Isn't that the whole idea of having two sets of batteries.
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Old 02-04-2022, 02:09 AM   #12
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5 year old chassis battery is near or at end of life. i look to replace my car/truck/rv batteries (flooded lead acid) at 5 years as preventative maintenance.
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Old 02-04-2022, 09:15 AM   #13
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Mnoel: I sent you a PM with questions about your 3901. I have a 3401. Thanks
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Old 02-04-2022, 01:49 PM   #14
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So after some testing, I believe that the battery isolation module is faulty (stuck closed). It is a BIM 160. When I test the voltages on my chassis battery and my house batteries they all read the same values (12.6v).



When I disconnect the chassis battery and test the voltages, the chassis battery reads 13.5v, and the house batteries 12.6v. When I test the voltage between the Batt A terminal and ground on the BIM with the chassis battery disconnected it reads 12.6v (but should read 0v according to the manufacturer). Testing the Batt B connector also reads 12.6v.



When I reconnect the chassis battery, but disconnect the house batteries, I noticed that all my interior lights are still running. Testing the voltage on the BIM terminal Batt A to ground, and on Batt B to ground, reads 11.6v and continues to drop. Checking the voltage on the chassis battery (with the house batteries disconnected and the interior lights still on) now reads 11.1v.


With everything reconnected, the chassis and house batteries all read 12.6v again.



All these tests were performed with the shore power disconnected.


The module is supposed to have a 5-year warranty, so I contacted the manufacturer (Precision Circuits) about a replacement. I looked around online, and they are all out of stock, so I'll have to wait and see what they say.


Thanks everyone for the suggestions.
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