Chassis battery no longer charging

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Koz

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Sep 20, 2021
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Georgia
I own a 2005 Thor Magellan 36Z motorhome. Until recently, while on shore power, both the house batteries and the chassis battery received a trickle charge. I have never had issues wirh the house batteries. The chassis battery has died several times. I disconnected it, charged it, and all was good for a month or so, then again it would not crank engine. During those occasions, I verified that 13.4 volts was being provided to chassis battery while on shore power. The last time the engine would not start, I heard relays clicking in the engine compartment. I disconnected the battery, charged it, reconnected, and all is good, except it is not receiving a charge. I checked all fuses. Any thoights on why I lost chassis battery charging?
 

Kirk

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You may be correct about Thor charging the chassis battery but many motorhomes do not and I have no experience troubleshooting that aspect of a Thor product. If it were me I would pull the battery out and take it to a battery shop and have it load tested. Most will not charge you anything to do this. Another thing that could be a factor is electrolyte levels. Have you checked all cells to be sure that they are at proper levels? How old is the battery?
 

Koz

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Sep 20, 2021
Posts
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Location
Georgia
You may be correct about Thor charging the chassis battery but many motorhomes do not and I have no experience troubleshooting that aspect of a Thor product. If it were me I would pull the battery out and take it to a battery shop and have it load tested. Most will not charge you anything to do this. Another thing that could be a factor is electrolyte levels. Have you checked all cells to be sure that they are at proper levels? How old is the battery?
Replaced the battery. With the battery disconnected I previously metered 13.4 volts at the battery wiring while on shore power, zero now. Thanks, but not a battery issue.
 

Kirk

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Sorry! I was only trying to help. :unsure: If you would like, I can make a few suggestions based on many years of experience, but if you mean by that you prefer not, that's fine too.
 

Koz

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Not implying I am not interested in any suggestions. You may provide all and any thoughts. I was just trying to clarify, it is definitely not the battery. My guess is bad relay or converter, but I have no idea where to begin.
 

Ex-Calif

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Replaced the battery. With the battery disconnected I previously metered 13.4 volts at the battery wiring while on shore power, zero now. Thanks, but not a battery issue.
Well there certainly should be a paralleling relay but I don't know the specifics of your coach to tell you where it might be. If you don't have a wiring diagram you may have to trace any wires coming off the +ive terminal of the chassis battery. It will likely be the cable or a heavy 10-12gauge wire going to a relay.

I would not suspect the charger if the house batteries are getting charged.
 

Koz

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Joined
Sep 20, 2021
Posts
7
Location
Georgia
Well there certainly should be a paralleling relay but I don't know the specifics of your coach to tell you where it might be. If you don't have a wiring diagram you may have to trace any wires coming off the +ive terminal of the chassis battery. It will likely be the cable or a heavy 10-12gauge wire going to a relay.

I would not suspect the charger if the house batteries are getting charged.
Two wires to + of battery. One to starter, other to a relay in the control center in the engine compartment. I suppose I should contact Thor for a wiring diagram, or take it to a local RV place. I hate to think what that venture would cost.
 

Kirk

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Are you saying that the battery has gone completely to 0V? Or are you reading 0V on the leads to the battery, when lifted? The latter would mean that no charging power is being supplied. I think that the previous post is probably correct. There should be a relay of some sort to connect the voltage from the coach's converter to the chassis battery when shore power is available but open if not in order to prevent the coach from draining the chassis battery. What chassis does it have? I have been searching the internet for some electrical diagrams and so far have not found much of help but this one might help if it seems to be what you have.
attachment.php
 

Ray-IN

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Mar 16, 2014
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Are you sure, without a doubt the new battery is wired correctly? Did you take a picture of the old wiring before disconnecting the old battery? That is the only sure way to prevent an error.
 

Koz

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Joined
Sep 20, 2021
Posts
7
Location
Georgia
Are you saying that the battery has gone completely to 0V? Or are you reading 0V on the leads to the battery, when lifted? The latter would mean that no charging power is being supplied. I think that the previous post is probably correct. There should be a relay of some sort to connect the voltage from the coach's converter to the chassis battery when shore power is available but open if not in order to prevent the coach from draining the chassis battery. What chassis does it have? I have been searching the internet for some electrical diagrams and so far have not found much of help but this one might help if it seems to be what you have.
attachment.php
Battery was down to 10v. The zero reading was at battery cables when disconnected from battery. As you said, no charging while on shore power. The chassis is a 2005 Worlhorse W22.
Are you sure, without a doubt the new battery is wired correctly? Did you take a picture of the old wiring before disconnecting the old battery? That is the only sure way to prevent an error.
I'm sure battery is connected properly. 1 back wire to ground, 2 red to positive, one to starter and other to battery control center. In addition, cable lengths won't permit wiring to other terminal. Thanks
 

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