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12v system issues

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Paul T

RVF Regular
Joined
Jan 20, 2024
Messages
5
Hi, I have a bighorn 3870 fb. I realized that my 12v system will shut down when shore power goes out, so no 12v at all. When I tried to turn on the inverter two error codes came up. Both indicated no battery or low battery. My batteries are both at 13.5 and 13.7. Between the batteries and the inverter is the circuit breaker followed by a buss fuse then to the transfer switch which is plugged into the inverter. I’ve found that where we are located it’s a $200 plus time just to have a repair company come out. I’m hoping someone can give me an idea of how to isolate which unit has failed. Please keep in mind that my multimeter skills are limited to checking dc and ac voltage unfortunately. Thanks for any advice.
 
How old are the batteries? Many people take comfort in measured voltages such as your 13.5 and 13.7 VDC but please understand, if those two batteries cannot deliver much amperage, they are dead.

Volts x amps = watts or power. The ability to do useful work.

Rick
 
I am one of those insanely priced repair guys. When you shut off shore power, it does not shut off 12 VDC. What does shut it off is the disconnect switch for storing the camper or just turning off the 12 vdc power. There is a momentary contact switch, probably near the door that says something like disconnect or store. It will turn on all the 12 vdc things until the batteries run down. If you don't have it on, the converter is supplying the power while hooked to shore power. The batteries need to be turned on most times in order for the converter to charge them also.
 
I am one of those insanely priced repair guys. When you shut off shore power, it does not shut off 12 VDC. What does shut it off is the disconnect switch for storing the camper or just turning off the 12 vdc power. There is a momentary contact switch, probably near the door that says something like disconnect or store. It will turn on all the 12 vdc things until the batteries run down. If you don't have it on, the converter is supplying the power while hooked to shore power. The batteries need to be turned on most times in order for the converter to charge them also.
Hi, thanks. If I understand you correctly you are talking about the 12v shut off switches. They are turned on to allow the batteries to be operational in case of a power outage. So that would poin to another issue. Is it possible that the batteries read 13.5v but they don’t have any amperage available to operate the syste? They are 6 years old and always plugged into shore power.
 
6 years is getting on in age. I would have to do an amp test to verify battery condition. You do not turn on the 12 vdc in case of power outage. 12 VDC runs your whole rig, all the time. What kind of rig do you have?
 
Ok, a Bighorn so a 5th wheel. When you pull the shore cord, unless you have turned something off, you will still have lights, slide controls, leveling systems, water pump, and the furnace will work, and the fridge unless you have a residential. My guess is a fuse is blown in the front compartment from your batteries to the main panel. Possibly even a resettable fuse, not the self resetting type.
 
Hi, thanks. If I understand you correctly you are talking about the 12v shut off switches. They are turned on to allow the batteries to be operational in case of a power outage. So that would poin to another issue. Is it possible that the batteries read 13.5v but they don’t have any amperage available to operate the syste? They are 6 years old and always plugged into shore power.
The test is called a load test! Harbor freight has a fairly cheap load tester.
 
Hi, I have a bighorn 3870 fb. I realized that my 12v system will shut down when shore power goes out, so no 12v at all. When I tried to turn on the inverter two error codes came up. Both indicated no battery or low battery. My batteries are both at 13.5 and 13.7. Between the batteries and the inverter is the circuit breaker followed by a buss fuse then to the transfer switch which is plugged into the inverter. I’ve found that where we are located it’s a $200 plus time just to have a repair company come out. I’m hoping someone can give me an idea of how to isolate which unit has failed. Please keep in mind that my multimeter skills are limited to checking dc and ac voltage unfortunately. Thanks for any advice.
One thing that jumps out at me is that your batteries are not at 13.5 or 13.7v. This is charging voltage and to find out the actual voltage of your batteries, you have to disconnet them and let them sit (rest) for a few hours. Doing this you should find something close to 12.7v for healthy batteries. If the resting voltage is down around 12.1 they are basically dead.

Resting voltage is a test you can do with your multi-meter and it will give you an idea of the condition of your batteries although voltage alone is not a great indicator of battery health. Also as stated above six year old lead acid batteries and bound to be about used up and getting that much life out of RV batteries is actually fairly unusual.

This is a good article on battery charging and health: https://deepcyclebatterystore.com/how-to-maintain-batteries/
 
But if he thinks unplugging shore power shuts down the entire camper he is not using his 12 volts system. There is a disconnect somewhere in the camper and his thinking.
 
But if he thinks unplugging shore power shuts down the entire camper he is not using his 12 volts system. There is a disconnect somewhere in the camper and his thinking.
Or his house batteries are to weak to provide sufficient power when unplugged. That’s why I suggested he test them at their resting voltage (since he just has a multi-meter) to determine the relative health of the house batteries. It may not be a disconnect at all but simply bad batteries although if this were the case he should at least have 12v lights.
 
But if he thinks unplugging shore power shuts down the entire camper he is not using his 12 volts system. There is a disconnect somewhere in the camper and his thinking.
Lol, well you are right, I’m not using the 12v system because without sufficient battery the inverter goes into a fault mode. Once the shore power is reconnected I can turn on the inverter. It’s a seamless system that just takes over automatically once a power outage hits but without the batteries operating the inverter it is not possible for the inverter to power on. I’m going to follow the advice of resting my batteries and then taking the voltage. Thank you for your reply though, I appreciate the thought.
 
Or his house batteries are to weak to provide sufficient power when unplugged. That’s why I suggested he test them at their resting voltage (since he just has a multi-meter) to determine the relative health of the house batteries. It may not be a disconnect at all but simply bad batteries although if this were the case he should at least have 12v lights.
Thank you for the idea, it makes sense to me considering the batteries are 6 years old. They have been active since day one but never ever used. I appreciate the reply and will let you all know the final resolution.
 
This is a current life reality at my rig right now!!!

My system!

24volt system and 12volt system 500w solar on 12volt system. 2000w solar on 24volt system.

At this time the 12volt system needs a battery, or super capacitor. This is how it is behaving!

The batteries must be jumped in the morning due to an under 8 volt reading that the solar controllers won't calculate proper system voltage, therefore shuts down. So you may think the battery would require hours to give a 13.× reading. However the battery reads full charged in only one hour! The system functions as would be expected with a quality bank all day, but if I do any water pumping greater than let's say fill a 3 quart pot! The charge controller shuts down with a battery voltage under 8 volts. At this time nothing on the 12 volt system works including the light's.

So my battery charger is connected and plugged into my 24volt system. All is well!!! Now if I unplugged the fuses in my 12volt system, I would be able to use my 12volt light.

To clarify! I took the converter out several years ago when it failed, and did not replace it! They don't play well with off grid installation, so they are worthless to me.

Battery plates plate with antimony as I have discussed in other threads, and load testing is the way you see if that is the issue!!!
 
If the batteries were so bad that the lights did not even work, it would be killing the ability of the converter to supply power when on shore power even. They can run the rig for the most part on their own, but add dead batteries and they will not power slides and such and many times the lights are dim.
 
This is a current life reality at my rig right now!!!

My system!

24volt system and 12volt system 500w solar on 12volt system. 2000w solar on 24volt system.

At this time the 12volt system needs a battery, or super capacitor. This is how it is behaving!

The batteries must be jumped in the morning due to an under 8 volt reading that the solar controllers won't calculate proper system voltage, therefore shuts down. So you may think the battery would require hours to give a 13.× reading. However the battery reads full charged in only one hour! The system functions as would be expected with a quality bank all day, but if I do any water pumping greater than let's say fill a 3 quart pot! The charge controller shuts down with a battery voltage under 8 volts. At this time nothing on the 12 volt system works including the light's.

So my battery charger is connected and plugged into my 24volt system. All is well!!! Now if I unplugged the fuses in my 12volt system, I would be able to use my 12volt light.

To clarify! I took the converter out several years ago when it failed, and did not replace it! They don't play well with off grid installation, so they are worthless to me.

Battery plates plate with antimony as I have discussed in other threads, and load testing is the way you see if that is the issue!!!
If you are off grid, you are not having access to limitless 120ac so a convertor makes no sense.
 
If the batteries were so bad that the lights did not even work, it would be killing the ability of the converter to supply power when on shore power even. They can run the rig for the most part on their own, but add dead batteries and they will not power slides and such and many times the lights are dim.
So you have never had batteries that were fully charged, but could not supply a reasonable load!!! Amazing!!! That is how batteries on constant charge give up the ghost in most off grid systems.

They don't put a load on the converter/charger, they just won't give up their charge.
 
I had one last week that was failing faster the more 12v loads were activated. I pulled the battery leads and tested it a 6.7 volts. Which came first? The failed battery or failed converter? Both were ruined.
 
I had one last week that was failing faster the more 12v loads were activated. I pulled the battery leads and tested it a 6.7 volts. Which came first? The failed battery or failed converter? Both were ruined.
Guess that would depend on which one failed first!!!

If the battery just would not give up the charge, the converter would not be guaranteed to fail. If however the battery puts a load on the converter, both could be bad, and likely the battery would have failed first.
If the converter failed first and the owner didn't abuse the battery then the battery may be recoverable.
 

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