Super-simple 12v power source for fridge?

Martinjmpr

Wiffleball Batter
As I posted here:


I have a new truck. The Suburban is currently being used by our daughter-in-law until they can replace her old Traverse that died a couple of weeks ago.

In the meantime, camping season isn't over for us. We have 3 camping trips planned. 2 of them we will have shore power so they aren't an issue but the next one coming up we will be boondocking. I'd like to bring the TruckFridge (though it's not 100% necessary now that we have a 3 way fridge in the trailer) but that raises a problem, how to get power to the 12v fridge:

First of all, contrary to my previous experience where Domestic branded vehicles have 12v accessory power on all the time, on my new-to-me F-150, the accessory power shuts off after you open the door. I understand this can be changed using the ForScan tool but as of right now, once I shut the ignition off I have no 12v power source.

Much as I'd like to just do a 2nd battery setup like I had on the 'Burb, I don't think that's feasible on the F-150. This new truck has so many sensors, computers, smart alternators, etc, that I'm afraid introducing a variable like that would wreak havoc with my complicated electrical system.

I'm sure it can be DONE - with enough time, effort and MONEY anything is possible. But as I thought about it last night, I wondered if maybe I was overthinking this.

A second battery is not the objective - the OBJECTIVE is a way to reliably power the fridge.

So I got to thinking, what is the most basic, stone-axe simple way of getting power to the fridge without having to mess with the wiring on the new truck?

And then I came up with an idea that I thought I'd bounce off the folks here, since you're all pretty knowledgeable with these things.

My idea is this: I'd get a decent 12v deep cycle Marine/RV battery, the kind with the wing-nut terminals on it. Maybe a Group 27 or even a Group 31. I'd try to get at least a 100ah battery. Then I'd get a simple plastic box for the battery, with a strap handle. Put a fused 12v power outlet onto the battery using ring terminals (probably fused at 15a - is that too high? Should I do 10a or even 7.5? I doubt the fridge ever draws more than 5a.) Make sure the battery is fully charged, plug in and - VOILA! Done!

Sure, there's no way in this setup to CHARGE the battery. But for a 3 day camping trip, I'm thinking a 100ah+ battery should work fine. When I get home, I'll put it on the home charger and charge it back up.

I can also put an SAE connector on the ring terminals and connect it to my solar panel if needed. On a nice sunny day I can get about 5.5a out of the solar charger - which should be enough to offset the power draw from the fridge.

EVENTUALLY I'll build a true "power box" that connects to the truck, most likely with a DC-DC charger.

But in the interim, is there any reason why this setup WOULDN'T work, at least in the short term? Best thing is I could put it together from easily available parts in my garage in a matter of an hour or so.

All input is welcome!

PS Since the battery box will likely sit in the cab of the truck I'm leaning towards an AGM vs a FLA, just so it will be sealed. More expensive, I know, but worth it I think.
 

dreadlocks

Well-known member
But for a 3 day camping trip, I'm thinking a 100ah+ battery should work fine.
Highly Unlikely... dunno what fridge you have or its specs, but they can easily consume 20AH+ a day, and if you discharge a 100ah battery more than 50% it'll be dead in short order.. so two days if your lucky enough to have a pretty efficient fridge.. maybe the solar will let you hit day 3, but maybe not unless you can guarantee it direct sunlight all day long w/no shade or forest canopy.. none of this can be known until you measure your fridge's average daily consumption out in the field.

Buy a cheap FLA, sounds like your going to be abusing the living hell out of this thing and it wont last long.. even less long if it was an AGM.. you dont need sealed, not with those loads its never going to gas out or cause any danger.. heck my vehicle has a FLA under my seat, put there by the manufacturer.. no issues at all.. put it in a battery box and forgetabout it.
 
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jadmt

ignore button user
my experience with my ARB 50 is yes that will work and power your fridge for at least 3 days if your truck fridge is like my arb 50. I ran mine in my garage for 4 days off a 100ah battery to see how it would do and it was still running fine when I unplugged it. you could also run a solar charger on the stand alone battery.
 

dreadlocks

Well-known member
I have an ARB 63, and had a 100AH AGM Solar Generator w/120W of solar.. without solar, no way it was making it to day 4 without ruining the battery.. and with solar and me never leaving camp so I could ensure the panel was always in the sun, I coulda got 4 days but the battery never got fully charged until I got it home so the battery was completely shot half way through its 2nd season.. On average it worked allright for weekend outings, but anything longer than 2 nights and I was in a losing battle, especially if I left camp for most of the day only to return and see the panel had ended up in the shade for the majority of its time.

Its one thing to test at home, its another thing in the field.. Are you opening the fridge regularly? adding in more beer to cool down? pre-chilling everything on mains power or battery? putting it in less than ideal thermal conditions (ie direct sun or locked in a hot vehicle)? all these things can make your test runs completely useless in the field.
 
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jadmt

ignore button user
I have an ARB 63, and had a 100AH AGM Solar Generator w/120W of solar.. without solar, no way it was making it to day 4 without ruining the battery.. and with solar and me never leaving camp so I could ensure the panel was always in the sun, I coulda got 4 days but the battery never got fully charged until I got it home so the battery was completely shot half way through its 2nd season.. On average it worked allright for weekend outings, but anything longer than 2 nights and I was in a losing battle, especially if I left camp for most of the day only to return and see the panel had ended up in the shade for the majority of its time.

Its one thing to test at home, its another thing in the field.. Are you opening the fridge regularly? adding in more beer to cool down? pre-chilling everything on mains power or battery? putting it in less than ideal thermal conditions (ie direct sun or locked in a hot vehicle)? all these things can make your test runs completely useless in the field.
I use it all the time camping which I do all the time as I am retired. camped in Moab in 105* for a week no way to get out of the sun and beer stayed frosty :). I have done several 4 day boondockers. Maybe I got a faulty battery from the factory :)
 

Martinjmpr

Wiffleball Batter
Good input, thanks. I may try with a cheaper battery before I invest $$ into an AGM.

For a point of reference, my Suburban has a 68ah AGM as the "house" battery. Last year we did a 4 day camping trip without ever starting the truck, so I know that from at least 4:00pm on Thursday until roughly 10:00am on Sunday, the truck was never started (and thus the battery was never charged) and it seemed to work fine. So that's 66 hours right there.

In the upcoming trip, we will likely arrive at the campsite around 2:00 PM on Friday and leave around 10:00 AM Sunday, so that is 44 hours on the battery. I would think a 100ah battery would be well up to it if the 68ah battery lasted for 66 hours, especially if I plug the 100w solar panel into the battery for a few hours on Saturday to charge it up.
 

ducktapeguy

Adventurer
That's basically the setup I have, with a few extra gizmos for convenience. I'm running off a group 35 starter battery (because I happened to have a spare one laying around) and although it works, I've killed the battery capacity in about a year from all the deep discharging. Still runs the fridge overnight, but capacity has diminished about 40-50%. Next battery will be a deep cycle.

Power draw on the fridge is highly dependent on use and environmental factors, it's possible it might last 4 days if the contents are pre-chilled and outside temps are cool, or it might last 1 day in the hot desert sun without pre-chilling. If you start with some frozen water bottles and use the fridge like and ice chest you can get 2 days with almost no energy usage.

A solar panel can offset a lot of the energy used and extend that time almost indefinitely if you have enough sunlight and temperature are mild. I just recently installed 100W solar panel and can probably get 4-5 days even with a bad battery and a bit of driving to keep the battery charged. You can charge from the stock wiring if you don't let the battery run down too much and have the fridge running at the same time.
 
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chmura

Adventurer
In my previous 4runner I had a single Group 31 AGM Northstar battery that I installed myself and ran thicker gauge wire to the back of my 4runner to reduce the voltage drop (never use the factory 12v source in the back). That being said I ran my ARB 50 qt fridge for 3 days straight without starting the vehicle numerous times without issues. I typically move camping locations every 1 or 2 days, but one time my vehicle sat for 3 days wtih fridge running. Vehicle started up fine the that morning.

I sold the 4runner and now I have a Tacoma. I am thinking of having a dedicated isolated battery for running my fridge and accessories. Redarc makes a really good dc-dc charger that when starting your vehicle it can charge your AGM battery to 100% quickly, has solar input also. Your cars alternator does not provide the correct voltage to properly charge an AGM battery. So in my previous 4runner I always hooked up a in the garage to top it off. For long term this is not ideal better to have a dedicated dc-dc charger IMO.

 

DaveInDenver

Middle Income Semi-Redneck
I have a battery like you're describing. Put a set of military terminals and Powerpole & fuse pigtail on the cheapest Walmart 1-year POS I could find locally. It was I think about $85 including the $30 core charge since I didn't have one to trade.

I grabbed it as a place holder while I was dealing with an Odyssey warranty, which is why I got the seemingly too small size. I run a dual 25/35 pair in the stock location and it sat in the redundant slot for a couple of weeks (my ham radios run off the aux so I had to have something installed). Once I got my replacement this one became a beater, so to speak.

Since it was so cheap and will just be a core eventually I don't bother treating it nice. Run it flat a few times camping or operating radio on Field Day and then throw on a charger back home. It's been a trooper now for nearly 7 months. Still holds up at 12.7V after conditioning and rest. Just used it a couple of weeks ago on White Rim. Ran my Engel MT45 for couple days. I don't care if it runs well below 12V, which should (and likely will) kill it.

I wouldn't necessarily spend bucks on a good battery you want to last or trust long term. Doing this isn't good for them. But it can get you the last couple of trips.

IMG_2497_mid.jpg
 
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Martinjmpr

Wiffleball Batter
^^^^ That's a starter battery though, right? I would use a deep cycle if I was getting a new battery but I can understand the idea of "run what ya brung."

WRT core charge, if you're a cheap SOB like I am you put an ad in your local CL or Facebook and ask if anybody's got an old battery in their garage or back yard that they want hauled away for free. I've never NOT been able to find one in the space of a few hours.

Might seem silly to waste the time to avoid a ~$12 core charge, but money's money.... ;)
 

DaveInDenver

Middle Income Semi-Redneck
It's the lowest end battery, yup it's a starter (and judging by the weight this particular group 35 must be intended to turn over lawn mowers normally). It's not really possible to find a true deep cycle in group 35. There's really no market for something like that with just 50 to 65 A-hr. I run a pair of Odysseys for redundancy and being AGMs they are really better called "deep cycle tolerant". You'll be better served with a real flooded deep cycle.

CL is a good idea. Heck, I should have just driven up and down a few alleys and found one. Wasn't thinking it through being in a haste.
 

Martinjmpr

Wiffleball Batter
MATH/SCIENCE QUESTION:

Many battery advertisements only give the "cold cranking amps" and "reserve capacity" rather than Amp Hours.

So I came across this:


The reserve capacity of a battery is the number of minutes for which it can run at 25 amps of current without its voltage dropping below 10.5 volts. It roughly describes the amount of energy the battery effectively stores and technically specifies the battery's charge capacity. Voltage relates charge and energy by describing the amount of energy in each coulomb of charge. Ampere-hours is a different unit for describing the same quantity.

Multiply the reserve capacity by 60 to convert it to seconds. For example, if a battery offers a 100-minute capacity: 100 x 60 = 6,000 seconds.

Multiply this length of time by 25, which is the battery's amperage. Example: 6,000 x 25 = 150,000. This is the number of coulombs of charge in the battery.

Divide this answer by 3,600, which is the number of coulombs in an amp-hour. Example: 150,000 / 3,600 = 41.67. This is the number of amp-hours in the battery.

To convert in a single step, divide the reserve capacity by 2.4.

I seem to be having a problem with this equation.

For example, when I research an Interstated 27DC battery, the Interstate web site shows an amp hour rating of 88 amp hours. It also shows a "reserve capacity" of 160 minutes.

So if I go 160 minutes x 60 seconds = 9600 seconds. 9600 seconds x 25 amps = 240,000 coulombs of charge. 240,000 Coulombs / 3600 = 66.67. So how does Interstate show this as being an 88 ah battery?


What am I doing wrong here? Or is the equation above not taking something into consideration?
 

Martinjmpr

Wiffleball Batter
CL is a good idea. Heck, I should have just driven up and down a few alleys and found one. Wasn't thinking it through being in a haste.

If anything it kind of gives you an incentive to stockpile old batteries in your garage in case you need one to avoid the core charge which I'm pretty sure is the exact OPPOSITE of what the practice is supposed to encourage. Unintended consequences!
 

dreadlocks

Well-known member
"Deep Cycle" is mostly marketing snake oil, it has very little meaning anymore.. and even then, for the good expensive deep cycles, you still needa treat them well, especially with the added money.. they will tolerate going lower than 50% a few times, but if you make a habit out of it.. the'll die just as fast as a cheap starter battery.

The best bang for the least bucks is a pair of cheap 6v Golf Cart batteries from Costco/Sams Club, now those suckers will take some abuse and neglect and keep on going without breaking the budget.. you can get over 200AH of capacity for well under $200
 

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