Newbie question: Deep cycle to run ARB Fridge+ (2 Viewers)

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woytovich

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So I'm totally new to the deep cycle battery world. I've done some research and my head is spinning. I need some real-world, down to earth input.

My needs are pretty simple: 3-4 days max 3-4 times a year with occasional running/driving the truck for short periods to add some power back. ARB fridge, occasional 12v water pump and a couple of LED area lights for a while each evening - not a ton of demand. Usually this all happens in the summer here in the northeast. Weight is not an issue generally.

This is not a dedicated expo/camping vehicle so I'm leaning towards a portable battery box with the ability to hook it up to the truck for on-the-go charging and 120v charging prior to hitting the road.

I'm not too worried about the battery box part - I'm thinking a box + battery + DC-DC charger is the most flexible solution. I happen to already own an Optimate DC-DC charger that'll handle lead acid and LiFePO4.

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80ah seems to be the minimum I should consider?

Then there's battery type - yikes! AGM, gel, lead acid, lithium, LiFePO4.... I'm not looking to need to take out a mortgage for this project. I'm hoping to find the balance of cost and functionality.

Any input will be appreciated.

Mark
 
And to further muddy the waters... surprise surprise: I just uncovered this National Luna box I bought years ago when i had first considered a similar project.

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That NL battery box sounds ideal for your application. Just buy a group 31 AGM whatever deep cycle for it and call it done. You’ll get 3-4 days power without charging assuming a quality fridge and NE summer temps. A fridge cover helps a lot with reducing power consumption in my experience.

You don’t need a dual purpose (starting) deep cycle if running it in that box as a 2nd battery. So any marine battery should be fine.
 
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Given the National Luna box maybe it's best to just KISS and get a good AGM(?) Deep Cycle battery at 80-100ah?
On sale:
Renogy 100ah
Do "we" like this Renogy or is there a "better" choice?
 
I don’t know anything about it. The reality is that there are only a handful of USA battery producers and everything else is simply a rebranded exterior. Personally I just bought a Deka Intimidator AGM. I have a local dealer and prefer to visit brick/mortar over Amazon. If I need a warranty I go see a person and his name is Steve.
 
OK, so you figure out what the energy use of your devices is. Either it's given in the specs directly or you take the nominal current and multiply this by the average voltage of your planned 12V battery, say 12.4V or 12.5V if lead acid or 13V if LiFeP, and multiply that by the time the device is to be running. That will give you V * A * h = Wh. For a fridge you also have to multiply by the fraction of time it's running (like 1/2 time etc). And you really want to use the actual current draw, not just the maximum current possibly drawn, that's potentially tricky. Do this over the period you need to function without other power. Knowing the Wh, you can then figure out the Ah of the new battery by dividing the Wh by the average voltage of the system, and then add a safety factor for efficiency losses and future needs, say another 25%. That's the size of the battery you need to function over that period. (Actually you can do all that just with the current and not involving the voltage if the voltages are consistent, but the above makes more sense physically.) All the above is greatly oversimplified but should give you an idea of the size. Note, though, that in real life, if you pick a battery that ends up too small, it's trivial to add another one later on, so it's not a one way street. But if you get one that's too big it's $$ and space lost.

As to real life experience, with my hardware, I can last only about a couple of days running the fridge with a 100Ah battery.
 
Ordered up a Renogy 100ah.... gonna give it a go in the NL box.... MAYBE using my DC-DC charger instead of their isolator system.

THANK YOU ALL!
 
Report back in the fall with results. I think you’ll be fine based on my experience which has always included the fridge cover so get one of those. Without it I loose a day of power. Keep the sunroof and some windows cracked when ever possible. Park in the shade. High Interior ambient temps will reduce the time significantly. But you should not see the kind of temps I see out here in the desert without shade options.
 
I’ve never seen that Optimate charger before, it shows on the picture a “2A charge at 12v”. If you are planning to use that charger to charge your aux battery, you may want to check to see at what amperage and voltage it plans to charge the aux at. 2 amps is a super slow charge for a 60-100 ah AGM or LiFePo4.
 
Personally I'd recommend adding 100W of solar into your setup. If your vehicle is stationary for many days this can help dramatically, especially in a sunny environment. Even in rain and clouds you will still get a couple amps. When in the desert, even if it is over 90 and the fridge is running a lot, the panels generate more than the fridge consumes. I have a 55ah optima for my house battery (so really 27.5ah usable if I want the battery to last). My two cents. I like panels fixed to the vehicle, but some folks like the portable systems
 
I have been running a 63qt ARB fridge with a dedicated group 31 for. years. When I lived in Calif, I could get 2.5 days running the fridge continuously in 90 degree heat days. I found that if I power down my fridge at night when I sleep, I would only lose about 8-10 degrees in my fridge temp and I could get another day out of the battery.
 
^ From memory, I would guess that most group 31s are around 100Ah, maybe pushing to 120 or so. So your 2.5 days would be consistent with what I'm seeing given that your ARB is probably a bit more efficient than my 63L Edgestar and I'm thinking similar temps.
 
Something not really discussed here yet has been the efficiently of various fridges. I see longer than average run times off my single battery using an Engel as its one of the least power hungry fridges out there. It's start up draw is the lowest due to their proprietary swing motor. And constant running draw is lower than most. I've said it before and will again. While the Engel is lacking many of the fancy features it's still dead sexy in its simplicity. Kind of like an FJ40. Chart below from a recent Overland Journal review. My wife runs an EndelB in her outback. I need to run a dedicated power source for it as its start up draw has already burned out the OEM 12v cargo plug. Did the same in the Impreza before it.

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Something not really discussed here yet has been the efficiently of various fridges. I see longer than average run times off my single battery using an Engel as its one of the lest power hungry fridges out there. It's start up draw is the lowest due to their proprietary swing motor. And constant running draw is lower than most. I've said it before and will again. While the Engel is lacking many of the fancy features it's still dead sexy in its simplicity. Kind of like an FJ40. Chart below from a recent Overland Journal review. My wife runs an EndelB in her outback. I need to run a dedicated power source for it as its start up draw has already burned out the OEM 12v cargo plug. Did the same in the Impreza before it.

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I want to say they only had the fridges set to like 46 degrees during the tests. I wish they had done another test with them set a little lower because I never have my fridge set that high. I know they put the same about of mass in both of the fridges during the test but all but two of them have different interior volumes.
To me a full fridge has less air space and will probably hold temps better. So of course the smaller volume fridges should do better. I just see a lot of inconsistencies in their testing. The video also starts off with showing them at a business that sells National Luna.

To answer the original post... I recently added a Victron Energy Smart Shunt to my aux battery. Really liking how it shows battery voltage. current draw in amps and watts and also how many amp hours have been consumed.
I'm also waiting to have a weekend to test my new Renogy 100w suitcase solar panel and Victron Smart Solar controller. Based on what I've seen so far it should be more than enough to run the fridge and help recharge the battery from the previous nights use.
 
I completely agree there are flaws in the Overland Journal fridge test. (many other tests for that matter). This was their 3rd test. I will say the Engel has consistently been a top performer in the power draw category over the years. As has the National Luna. I've made my buying decisions mainly on that. I'm sure Overland Journal is sometimes at the mercy of what each manufacturer will send them. So it't hard to do apples to apples on size.
 
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^ From memory, I would guess that most group 31s are around 100Ah, maybe pushing to 120 or so.

About half of that usable on a lead acid.
 

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