# Is Solar Necessary for Boondocking with 12V DC Fridge?



## PSnartland (Nov 19, 2021)

Hi All, new to this forum.

We are purchasing a new travel trailer that comes with a 12V DC fridge. No propane option for fridge. Dealer has recommended installing a pair of GC15 6V batteries instead of the normal 12V deep cycle batteries, because we intend to use the camper mostly for boondocking/remote camping. I am concerned about running out of power overnight. We will have a gasoline generator, but I am concerned about how long we will have to run the generator to recharge the batteries every day. Do I need to install solar panels to keep the batteries charged up during the day? Or will the GC15 batteries and generator work well for us. Other power draws on the 12V system will be lights, furnace fan, water heater ignition.

Thanks for your help!


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## PSnartland (Nov 19, 2021)

The title of my post should have been "Is Solar Necessary for Boondocking with 12V DC Fridge?" Sorry for any confusion...


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## travis.farmer (Jun 26, 2021)

i fixed the title for you  for future reference, posts are editable, so it could have been changed by you by clicking the 3 dots in the upper right of the post. 

charging batteries with a generator depends on what your charger/converter output is. for example, mine is a 3-state (bulk, absorption, float) 100A charger. this style charger will get your batteries back up safely, and in a hurry, if i did my research right (nobody is perfect  ).

the reason for the two 6V batteries in series, versus one 12V is about storage capacity. 6V batteries have a lot more amps, but less volts. put two in series, and you have correct volts, with the larger amps stored. again, depends on my research.
I will just use two 12V batteries, myself, as they are easy to get, and replace, but i think the 6V batteries have a little more longevity in total life.

most RV fridges draw very little 12V power. as they don't use an electric motor powered compressor. but they take a while to get there, so get it cooled down early, and no door-flapping while you decide what to eat 

your RV furnace though will take a lot of power to run the blower. the electronic-ignition water-heater will likely not take much.

so assuming you have LED lighting, your biggest current draw looks to be the furnace. by my figuring, anyway.

in my experience, my old 35000BTU LP furnace would last out a 90AH 12V battery i had at first, for about one night. though the blower was weak by morning. with two good sized pickup-truck starter batteries, i could run all night, and have power for lights in the morning. with my old, and likely weak, charger (40A), i would leave the charger going all day, and it would be ready by night. with a better charger, i would have been ready sooner.

now, solar... i have one 100W panel, and it JUST maintains my battery enough to run the alarm system. but it is a old, and very weak battery. i just don't want it to blow up and leak acid everywhere, yet i can't afford a new set of batteries yet. 

solar panels are great when they get sun, if you have enough of them. but useless for any real power draw, if you have just one. full sun, mine charges about 10-15A i think, maybe less.

but anyway, welcome to the forum! it is a little slow here right now, but the more people posting, the more attractive it is for others to post  we are trying to bring it back, now that i am working to take care of as much SPAM as i can find.
I know there is a guy here that knows far more than I about camper electrical, so hopefully he will help too.

Again, Welcome!

~Travis


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## PSnartland (Nov 19, 2021)

Thank you Travis. I should have been more clear in my post... The fridge in our new camper is a 12VDC compressor-type fridge. Amp draw is 8.3 amps according to the manufacturer. The 6V batteries proposed by the dealer are 230Amp-hr GC15. I think this means that the batteries will last 230 Amp-hours / 8.3 Amps = 27.7 hours running just the fridge. Is that the right way to figure it?

I hear what you say about the furnace fan drawing considerable power also. As a guess, let's say it draws the same as the fridge, so for the overnight hours the draw would be an additional 66.4 amp-hours, taking the battery life down to 19.7 hours.

I've been trying (without much luck) to find a performance curve for the batteries, one which would show what the voltage would be after drawing our, say, 100 amp-hours of power. I think this is important, because the fridge will stop running if the voltage supply drops below 10.4 volts.

We are considering installing a 200 watt solar system permanently mounted on the travel trailer roof, but it is significantly expensive ($2100 from the dealer). Also being considered is a less expensive ($750) 200 watt solar system that is portable, but we have concerns about it being stolen while we are off exploring during the day.

Thanks again for all your help and insight, Travis. I really appreciate the time you're devoting to this.

Phill


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## PSnartland (Nov 19, 2021)

I also don't know yet what the amp rating on the converter/charger is, so I can't come up with a good estimate on how long it takes to recharge the batteries with the generator.


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## travis.farmer (Jun 26, 2021)

PSnartland said:


> The fridge in our new camper is a 12VDC compressor-type fridge. Amp draw is 8.3 amps according to the manufacturer. The 6V batteries proposed by the dealer are 230Amp-hr GC15. I think this means that the batteries will last 230 Amp-hours / 8.3 Amps = 27.7 hours running just the fridge. Is that the right way to figure it?


it is generally recommend that you never discharge below 50% for max lifespan of the batteries. so 230Ah with 17.7A (8.3 fridge, 9.4 for my furnace), is (230 / 2) / 17.7 = 6.55 hours. a voltage of around 12.25V is the general area of 50% discharged, but i recommend a coulomb counter battery gauge. i have this (not installed yet, so i don't know the performance): https://www.amazon.com/gp/product/B07FGFFHC6
from what i read so far of the manual, it stays connected to the battery, so it is installed BEFORE the battery cut-off switch, if installed. this is because if the battery is disconnected from it, you have to reset everything. there may be better gauges out there, but one that will tell you the percentage of charge or discharge is what you want.

You can use a volt-meter, in a pinch, but you would need to know the performance curve.
you can of course plot out your own curve by testing the battery yourself. just discharge the battery at a constant rate, like say 20A, and every 10mins, jot down the volts. do this until you get to 12.25 volts.
if you want to get really scientific, you could do this for a variety of constant amp draw curves (one constant amp draw per curve) 

but as i said above with the two 6V batteries @ 230Ah, if that is the case (with batteries in series, volts double, amps are the same. in parallel, the volts stay the same, and amps double), with a constant draw (neither the fridge, nor the furnace will draw constant for the full capacity of the battery  ) of 17.7A to 50% battery, you will get about six and a half hours.

i expect a little less than double that in actual draw, based on a half-on, half-off run cycle of the fridge and furnace. maybe even more if they happen to be efficient, and the fridge and camper have good insulation.

Hopefully i haven't bogged you down with numbers and insight  what i was getting at, is you should have more than enough battery capacity to run all night, from a full charge.

charging, is a whole different animal.  batteries like charging at a certain rate, and will only take what they like to have. in other words, you can only feed them as fast as they can chew the food. more batteries will need more charging current. but more charging current than you need, like my 100A charger, means you can run appliances AND still charge batteries at the full rate. but more than one charger will not necessarily charge faster, but will increase your total available amps while charging.
i like MPPT solar chargers, but i can't tell you why, as i was just told i should like them  
for charger/converters, i like 3-state charging. i feel they are better for the longevity of the batteries. in particular if you use low quality batteries like me (Wal-Mart brand deep-cycle batteries  , because replacement cost is cheap)

i may not even know what i am talking about, this is just from my research and experience. 

best i can say, get as many batteries as you can afford, and have space for. they will come in handy. remember to figure in your water pump too, if not on city-water. and use as little battery power as you can afford. this isn't a house with city-power coming in (though you can plug into city-power). not in a room, turn off the lights.  heating is most efficient if you maintain the same temperature. that way a warm-up after a cool-down (while away from camper) doesn't draw a huge amount of power and fuel. though if you are away for several hours, and there is no risk of freezing, it is ok to turn the heat off. (my experience  )

what did you have planned for a generator? i plan on a built-in for convenience in transport, but i would recommend a portable inverter generator. if it breaks down, or dies completely, they are easier to fix or replace. an inverter generator runs quieter, so other campers will hate you less.  

I look forward to hearing about your adventures  my 5th wheel camper is in the process of a major renovation, so it will be a while yet before i can have adventures of my own. 

~Travis


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## PSnartland (Nov 19, 2021)

Thanks, everyone, for all your input. My big concern is that it is winter now, and we are planning our first big trip (1 month or more in duration) in the new camper in April, shortly after taking it out of storage. I am concerned about finding ourselves running out of battery during the night and our food going bad or my wife getting cold. Maybe I'm being paranoid, but I can envision having to run the generator nearly constantly to keep the batteries topped up for the overnight. You're right, in that I certainly don't have all the answers needed to give accurate answers, and budget is certainly a consideration. Thanks again for all your help.


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## crawford111 (Aug 2, 2021)

a good solar generator with a couple of panels to move around to keep the best charge.


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## Happy Joe (10 mo ago)

I solar necessary?
No not really; if you can charge your battery(s) from the engine or tow vehicle every day or two they will usually support a 12 volt fridge for a couple of days if they are 100 amp hour batteries. My, not new, 35 amp hour lead acid deep discharge battery could keep the fridge running for a day but was seriously in need of a charge at that point..
So called solar generators are overpriced, IMO, but its your camping trip make up your own mind, about your gear.

I had a solid state/Peltier based cooler for a while but now consider them far inferior to a compressor type 12 volt fridge... my fridge will keep ice cream frozen, the Peltier cooler never could.

Enjoy!


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