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Old 09-22-2020, 04:08 PM   #1
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Coach batteries not recharging

I have a 37KT Thor Challenger and having just replaced my coach batteries with 2 6 volts, I found that the batteries are going down. I did a voltage check on the motor battery as well the coach battery and when I started the vehicle, the motor battery voltage increased due to the alternator. The coach battery didn't change. When I did the same thing with the gen set, the same results. The motor battery is recharging from both the alternator and the gen set. The coach battery is not recharging. Does anyone know where to start looking? Is it a fuse, relay, etc?

Thanks,
Mike
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Old 09-22-2020, 04:15 PM   #2
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Mike,


Let's get terminology agreed on:


Chassis batteries


House batteries.


Normally, alternator charges BOTH battery banks with a BATTERY ISOLATOR in between the alternator and batteries. The battery isolator can be diode-based or solenoid-based.


The converter or inverter/charger (powered by 120 VAC from shore power or generator) normally charges only the house bank.


SO, sure sounds like someone has changed your coach wiring.
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Old 09-22-2020, 04:33 PM   #3
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Quote:
Originally Posted by thepalmers View Post
I have a 37KT Thor Challenger and having just replaced my coach batteries with 2 6 volts, I found that the batteries are going down. I did a voltage check on the motor battery as well the coach battery and when I started the vehicle, the motor battery voltage increased due to the alternator. The coach battery didn't change. When I did the same thing with the gen set, the same results. The motor battery is recharging from both the alternator and the gen set. The coach battery is not recharging. Does anyone know where to start looking? Is it a fuse, relay, etc?

Thanks,
Mike
If you just changed your batteries, I'd go back and be sure you didn't miss a wire when you hooked up the new batteries.

I always take pictures before I dive into a project. I don't always trust myself.
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Old 09-22-2020, 05:49 PM   #4
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Only thing, I think, that makes sense is you left a cable off the house batteries.

If the house battery charger is charging the start battery, the the bi-directional isolation system is working, but only one way.

Did you change to 6 volt batteries from 12 volt ones ?
Take a picture of your battery compartment and cables and post it.
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Old 09-22-2020, 05:54 PM   #5
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Originally Posted by wolfe10 View Post
Mike,


Let's get terminology agreed on:


Chassis batteries


House batteries.


Normally, alternator charges BOTH battery banks with a BATTERY ISOLATOR in between the alternator and batteries. The battery isolator can be diode-based or solenoid-based.


The converter or inverter/charger (powered by 120 VAC from shore power or generator) normally charges only the house bank.


SO, sure sounds like someone has changed your coach wiring.


Thanks for your response, At this time, I think that the shore power is able to charge the "house" batteries. I was only able to get them to charge to 11.8V from 9.2V. The alternator and the gen set do not charge the house batteries. I know that they should, but at this time they are not. Not sure that the wiring has been altered, I am wondering if a relay or other has been disabled
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Old 09-22-2020, 05:56 PM   #6
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Only thing, I think, that makes sense is you left a cable off the house batteries.

If the house battery charger is charging the start battery, the the bi-directional isolation system is working, but only one way.

Did you change to 6 volt batteries from 12 volt ones ?
Take a picture of your battery compartment and cables and post it.
I had 2 6 volts batteries in prior. They have worn down and needed replacement. Your point about a lost wire is a possibility and will look into that. Thanks,
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Old 09-22-2020, 06:37 PM   #7
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On my motorhome's setup, BEFORE I attempt to start the engine (or generator) I always throw this switch to ON first. Then, once it has started, I ensure that the switch is in the OFF position.

I'm not sure if putting this switch to the ON position is necessary to start the engine, but I DO know that the generator WILL NOT start if the switch is in the OFF position. The generator will CRANK, but will NOT start, unless the switch is in the ON position. Once it has started, I place the switch in the OFF position so that I won't forget to do it later. The engine & the generator will continue to run, even when you put the switch to OFF.

If you have a similar setup, perhaps you have left the switch in the ON position, & if so, maybe it helped to drain your battery.
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Old 09-22-2020, 06:39 PM   #8
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Thanks for your response, At this time, I think that the shore power is able to charge the "house" batteries. I was only able to get them to charge to 11.8V from 9.2V. The alternator and the gen set do not charge the house batteries. I know that they should, but at this time they are not. Not sure that the wiring has been altered, I am wondering if a relay or other has been disabled

Shore power and generator are EXACTLY the same in terms of powering the charger, so you need to verify that the generator IS supplying 120 VAC to the coach.


If this is a smart charger, it is also possible that it is "smart enough" to not try to charge a deeply discharged battery (much below 12.0 VDC is DEAD). So, you may want to fully charge the house batteries and have them LOAD TESTED, as bad batteries can give all kinds of weird issues.


Troubleshooting the alternator is completely separate. A good place to start is at the BATTERY ISOLATOR. I don't now if yours is diode-based or solenoid-based.



All these things are pretty easy to troubleshoot for anyone familiar with RV 12 VDC systems.
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Old 09-22-2020, 06:42 PM   #9
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Originally Posted by Moxxi View Post
On my motorhome's setup, BEFORE I attempt to start the engine (or generator) I always throw this switch to ON first. Then, once it has started, I ensure that the switch is in the OFF position.

I'm not sure if putting this switch to the ON position is necessary to start the engine, but I DO know that the generator WILL NOT start if the switch is in the OFF position. The generator will CRANK, but will NOT start, unless the switch is in the ON position. Once it has started, I place the switch in the OFF position so that I won't forget to do it later. The engine & the generator will continue to run, even when you put the switch to OFF.

If you have a similar setup, perhaps you have left the switch in the ON position, & if so, maybe it helped to drain your battery.
"The switch." "The switch." "The switch." You say this like we know which switch you are talking about?
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Old 09-22-2020, 07:12 PM   #10
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Originally Posted by wolfe10 View Post
Shore power and generator are EXACTLY the same in terms of powering the charger, so you need to verify that the generator IS supplying 120 VAC to the coach.


If this is a smart charger, it is also possible that it is "smart enough" to not try to charge a deeply discharged battery (much below 12.0 VDC is DEAD). So, you may want to fully charge the house batteries and have them LOAD TESTED, as bad batteries can give all kinds of weird issues.


Troubleshooting the alternator is completely separate. A good place to start is at the BATTERY ISOLATOR. I don't now if yours is diode-based or solenoid-based.



All these things are pretty easy to troubleshoot for anyone familiar with RV 12 VDC systems.
Its not going to have a battery isolator, there went out if flavor back in the 2000s.

It will have a bi-directional isolation solenoid.
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Old 09-22-2020, 07:53 PM   #11
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"The switch." "The switch." "The switch." You say this like we know which switch you are talking about?
I was cracking up reading this. I too was wondering what SWITCH this person was/is talking about.

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Old 09-22-2020, 11:04 PM   #12
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Originally Posted by wolfe10 View Post
Shore power and generator are EXACTLY the same in terms of powering the charger, so you need to verify that the generator IS supplying 120 VAC to the coach.


If this is a smart charger, it is also possible that it is "smart enough" to not try to charge a deeply discharged battery (much below 12.0 VDC is DEAD). So, you may want to fully charge the house batteries and have them LOAD TESTED, as bad batteries can give all kinds of weird issues.


Troubleshooting the alternator is completely separate. A good place to start is at the BATTERY ISOLATOR. I don't now if yours is diode-based or solenoid-based.


All these things are pretty easy to troubleshoot for anyone familiar with RV 12 VDC systems.



Thanks again, your comment regarding the smart charger is likely right. I think I may have found the issue. My converter has 2 fuses on it for reverse polarity. I will check them tomorrow and see if they have been blown. Perhaps the person that changed the batteries inadvertently shorted the circuit.

Mike
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Old 09-22-2020, 11:14 PM   #13
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The switch, the switch, the switch?

Yes, the switch. I'm glad that it gave you so much joy.

Here is the switch that I was referring to. It is in the door well.Click image for larger version

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Old 09-23-2020, 07:15 AM   #14
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The switch, the switch, the switch?

Yes, the switch. I'm glad that it gave you so much joy.

Here is the switch that I was referring to. It is in the door well.Attachment 301995
Isn't that the common 'battery disconnect switch', sometimes referred to as the 'salesman' switch?

Why would you want to turn it off after you get the generator running? If I did that, it would disable much of my electrical.
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