We have a 5 year old 30' Rockwood trailer that we often use dry camping at a local county park that can get cold at night. We have two 6 volt batteries and a solar charger. Before we leave home I have both batteries fully charged. While dry camping we use our solar charger and are careful about our use of electricity. We use lanterns for lights, don't use the trailer's stereo, but never-the-less in the middle of the night when I'd rather be sleeping the low batter alarm buzzer goes off just after the furnace begins to work. This can happen even on our first evening out. When I turn off the furnace the reading on our control panel indicates there is plenty of battery power left. What could possible be going on to cause this problem? Anybody out there have an idea?

“and are careful about our use of electricity...”There’s “careful” and there’s “careful.” A solar system should provide all the juice you need for a night’s camping and fully recharge the batteries the next day. Did you do an energy survey? Once completed, are your battery amp hours at least double that? Preferably 2.5 to 3. Do you have at least solar panels providing 1 watt per battery amp hour? Is your controller and your wiring adequate? Using battery lanterns and no stereo or TV stinks!Tell us in detail what batteries you have.

Your batteries may not be so fully charged when setting out as you think. They are "collapsing under load" and the voltage bounces back with no load.How do you decide they are fully charged? Hydrometer reading needed to confirm this. What is your method of keeping them charged when home? How much of a solar charger is that? what converter does your Rv have ?You have come to the right place, but be prepared to answer a bunch of questions! :)

How old and what (exactly) type of batteries are these? Amp Hours? Deep cycle? Brand? Wet cell that require you add water or something else?

If you are judging that the batteries are fully charged by the little 3 or 4 red light meter built into the trailer that's not a good reading. That little meter is useless. You would need either a battery gauge with a shunt to measure amp hours in vs. amp hours out or you would need a hydrometer to know they were full.I suspect one of your batteries has a bad cell and thus they both need replacing. Another possibility is that you have some very poor, loose, or coroded connections that are a high resistance under load.

At least use a digital volt meter measure battery voltage.

Furnace and battery | Good Sam Community

John_Hammond
Explorer
Jan 22, 2019
Here are a few of the recommendations I've received regarding running out of power when dry camping and running the furnace on battery power: Please comment on what you think of these ideas:
1) Keep the overnight temperature set lower.
2) Charge the batteries during the day by running the truck engine while the truck is connected to the trailer.
3) Leave the truck connected to the trailer at night so the truck battery can supply extra power to run the furnace.
4) Get a larger solar panel.
5) Buy two more batteries and swap them during our trips.
6) Use sleeping bags to stay warm.
7) Clean the battery terminals (done).
8) Buy a generator to change the batteries during the day.

Anyone have any thoughts about these ideas?

John
jkwilson
Explorer III
Jan 22, 2019
maillemaker wrote:
Steve ... maybe I'm misreading your diagram, but what 12V Group 29 batteries are you using that have a capacity of 210 AH each?

The image is a random one I pulled off the internet to show the wiring schematic. Ignore battery specifics.

Steve

My guess is whoever drew it confused RC with AH. Most 29s are rated 210 minute RC.
BFL13
Explorer II
Jan 21, 2019
Doug R said something I am not sure is correct, that if the fan slowed down from too low a voltage ( he said under 12.5v!!!) the sail switch would open and the then no heat.

I have not seen that happen with much lower voltages than that, but I would wonder about a low speed setting for the fan wrt the sail switch's operation. Anyway, I can't alter the furnace fan speed.
MrWizard
Moderator
Jan 21, 2019
Mine doesn't let you change fan speed for heat/furnace
bpounds
Nomad
Jan 21, 2019
John Hammond wrote:
...I don’t have access to the solar panel now, but it measures about 6’ wide by 2 ½’ tall in two panels that fold in half for storage...

That's not enough solar to replace what your heater alone uses each night. So each day you will lose ground, in terms amps stored. That doesn't explain an issue on day one perhaps.
bpounds
Nomad
Jan 21, 2019
I'm pretty sure FLO means Float, not full. It'll need to sit on float for days to actually be 100% SOC.

I wonder how many people run their heaters with the fan on low versus high? I always run ours on low fan speed. I've found it is easier on the batteries, does just as good a job of heating the space, and is quieter when we're trying to sleep. There is less air flow, but the air is warmer.
MrWizard
Moderator
Jan 21, 2019
A pair of 4Ds could have those numbers
But they have both posts on one end of the battery
Not on opposite ends like car jars
maillemaker
Explorer
Jan 21, 2019
Steve ... maybe I'm misreading your diagram, but what 12V Group 29 batteries are you using that have a capacity of 210 AH each?

The image is a random one I pulled off the internet to show the wiring schematic. Ignore battery specifics.

Steve
MrWizard
Moderator
Jan 21, 2019
Might get a 4D size with 210 ampHrs

But I've not seen, a group 29, with that many ampHrs
pnichols
Explorer II
Jan 21, 2019
maillemaker wrote:
So I don't know much about those 6 volt batteries.

What I can say is our Class C as it came from the factory only had room for a smallish house battery under the hood. I forget the size.

But it would not run the furnace for a weekend outing.

So, I added a larger Group 29 12VDC battery in one of the under-house storage compartments, and wired it up with the existing battery under the hood. This gave us enough battery power to run the furnace at night for the weekend.

When these batteries died, I ditched the smaller under-hood battery and replaced it with a terminal block, and wired this to a pair of Group 29 12VDC batteries in the under-house storage compartment. Because they were in close proximity it now made it easy to have the + and - main terminals connect to the + terminal of one battery and the - terminal of the other battery, which is the proper way to gang two batteries together:

The new setup easily runs the furnace all weekend long as needed.

Steve

Steve ... maybe I'm misreading your diagram, but what 12V Group 29 batteries are you using that have a capacity of 210 AH each?

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