Super-simple 12v power source for fridge?

DaveInDenver

Expedition Leader
If I'm understanding you both then I think I'm good. My "long" connection would be from the starter battery under the hood to the DC-DC charger in the cab. The run from the DC-DC charger to the battery being charged would likely be less than 2 feet, maybe less than 1 foot.
That'll work A-OK. That's the beauty of using the DC-DC charger. Just need the feed to be large enough to be safe and the rule of thumb charts are fine for that.
 

Martinjmpr

Wiffleball Batter
That'll work A-OK. That's the beauty of using the DC-DC charger. Just need the feed to be large enough to be safe and the rule of thumb charts are fine for that.
Yeah, so really my only conundrum now is that since I plan on keeping this all in the cab, do I go for the spendy AGM or a "good enough for now" FLA? There's a lot to be said for the "buy once/cry once" way of doing things so I'm leaning towards getting an AGM to go in the box. That way I don't have to worry about outgassing or topping off water. But it's almost 3x the cost of an FLA!

On the flip side, for what we use the battery for (i.e. to run the fridge while we are on a camping trip) I would think an FLA would work fine. It's not like the battery will be in the truck 24/7. It will only be in the cab when we're on a trip.
 

DaveInDenver

Expedition Leader
Yeah, so really my only conundrum now is that since I plan on keeping this all in the cab, do I go for the spendy AGM or a "good enough for now" FLA? There's a lot to be said for the "buy once/cry once" way of doing things so I'm leaning towards getting an AGM to go in the box. That way I don't have to worry about outgassing or topping off water. But it's almost 3x the cost of an FLA!

On the flip side, for what we use the battery for (i.e. to run the fridge while we are on a camping trip) I would think an FLA would work fine. It's not like the battery will be in the truck 24/7. It will only be in the cab when we're on a trip.
The outgassing and spilling are worth mentioning inside a well sealed vehicle cabin.

The outgassing potential is during charging, so if you're only charging at home or in camp with the battery outside that's lowered risk. Putting the battery inside a box and kept upright helps reduce chance of spilling.

So for you it's a relatively low risk to go FLA probably. Just generally be aware of risks when mounting batteries inside occupied and sealed spaces, so boxes and venting.
 
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dreadlocks

Well-known member
What kinda loads you putting on it again? just a fridge right... yeah there's no way <5A of power gonna cause any grief w/a FLA.. now if you were daily draining it down with 200A+ loads and then recharging it with 50A+ charging then you might get some outgassing, but the thing is.. you need some serious engineering to contain hydrogen, our earth cannot even hold onto it.. unless your vehicle is the perfect container, there's no way your battery is going to generate enough concentrations to do anything... put it in a battery box so if any battery acid gets out it'll contain it, not that its likely with a low discharge/charge rate.

My SUV has a FLA battery installed in the passenger cabin, it was put there by the manufacturer.. its right under my seat inside a plastic box and thats it.. spending more money for a sealed battery is much ado about nothing IMO.. just dont bulk it up from nearly dead with a dumb 100A shop charger while its in your vehicle, and I doubt you'll ever have any concerns.. your DC charger will keep it from outgassing much if it at all w/a proper charge profile.
 
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dreadlocks

Well-known member
When I ran a small fridge load off a FLA, I checked the water regularly but the only time I ever added anything was at beginning and end of season right before and after I put it on a battery maintainer for the winter.. and even then it was a very small amount... When your running 0.05C or less on a battery, it should not going to be consuming much water at all.. 90 days is a bit excessive if your not a full timer.

Now if you start putting huge loads on the battery, like a winch, inverter, air compressor, whatever.. and you'll find you needa keep a closer eye on it.
 

Runt

Adventurer
Your idea will work.

For your exact scenario I priced out the battery, screwing around etc and opted to spend $ 200 more on a Goal Zero Yeti Lithium power pack for our 4Runner. Reasons were it can be plugged into an inverter when driving to charge and has an input and out put meter so you can monitor your use or locate your solar panels location to get max charge, its light weight therefore easy to strap down and sealed for inside cab use. The Goal Zero Yeti Lithium will power my 60 L ARB fridge in 25 degree Celsius weather for two days easy. This is even with chilling a case a beer from room temperature to - 3 C each day....I like beer. All battery life will vary depending on temperatures your fridge is subjected to as well as how many times you go in and out...I could likely get three days but two is for sure.
 
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DaveInDenver

Expedition Leader
What kinda loads you putting on it again? just a fridge right... yeah there's no way <5A of power gonna cause any grief w/a FLA.. now if you were daily draining it down with 200A+ loads and then recharging it with 50A+ charging then you might get some outgassing, but the thing is.. you need some serious engineering to contain hydrogen, our earth cannot even hold onto it.. unless your vehicle is the perfect container, there's no way your battery is going to generate enough concentrations to do anything... put it in a battery box so if any battery acid gets out it'll contain it, not that its likely with a low discharge/charge rate.

My SUV has a FLA battery installed in the passenger cabin, it was put there by the manufacturer.. its right under my seat inside a plastic box and thats it.. spending more money for a sealed battery is much ado about nothing IMO.. just dont bulk it up from nearly dead with a dumb 100A shop charger while its in your vehicle, and I doubt you'll ever have any concerns.. your DC charger will keep it from outgassing much if it at all w/a proper charge profile.
Gassing rates are given dependent on voltage. VRLA is generally said to produce 0.0185 cc/hr per A-hr per cell at 2.3 V. If you push them too hard, though, it goes up 20 fold at 2.5 V/cell. So charging has to be controlled in enclosed spaces. For the UPS batteries I've seen a typical 100 A-hr AGM battery will produce around 10 cc/hr at 2.3 V/cell float and around 20 cc/hr at 2.4 V/cell. So you can see that for AGM it's manageable.

For a flooded the rate is much higher and is significant in small enough space without an exchange of air. A FLA can produce about 0.42 liters (e.g. 420 cc) of hydrogen at >2.35 V/cell with each amp-hour per cell. So a 100 A-hr 12V battery subjected to an overcharge might produce 50 liters of hydrogen and 25 liters of oxygen.

Hydrogen becomes explosive at 4% concentration, so you can do the calculations to know how much air needs to be exchanged. A room full of batteries is of course a much different issue than under the back seat of your Audi. Even with a couple of large house batteries it's not unsurmountable but it should be considered IMO.
 
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Martinjmpr

Wiffleball Batter
(y)

Good input from everybody. This puts my mind somewhat at ease about going with the less expensive FLA from Costco.

Looks like I may be able to put the DC-DC charger under the back seat in the "tray" at the very back. I'll probably secure it to the floor somehow (I'm loathe to screw things into sheet metal, especially given that my F-150 is mostly aluminum, so I may look at rigging up some kind of strap? Or maybe I can bolt to the seat frame somehow?)

After that it's just a matter of running an appropriately sized wire from the battery back into the cab. If I need to do AC charging from a 120v source (like before or after a long trip) I'll charge it in the garage. As I said, the battery box will only be in the cab of the truck when the fridge is in there. The fridge lives in our (insulated) garage in winter. I'll put the box on a battery tender/trickle charger over the winter.

As much fun as it was to do the dual battery setup in the Suburban, this is probably an easier, cheaper and more flexible way to go.

Especially the "cheaper" part. I spent almost $300 just for a 68ah AGM battery on the Suburban because it was the only one that would fit in the factory location!
 

Martinjmpr

Wiffleball Batter
Update: Decided to be frugal and go with the FLA from Costco. $111 out the door which includes the core charge (I'll find an old battery on a local "next door" message board or CL to get my $15 back!) When I got the battery home it measured 12.5v, or about 80 - 90% for an FLA. I threw it on a 10a "dumb charger" in the garage for an hour or so to get it up to 12.7.

This weekend will be the first test - camping for 2 nights with no hookups. Temps will be on the cool side so not a tough test of the system.

One thing I discovered right away (which I should have known): The "carrying handle" on the case top is useless once a battery is in there. Unless you have the arms of Popeye you're not likely to be carrying a 75+ lb battery one handed! Instead I use the two handles on the side of the box bottom to carry it.

I have a 12v USB port and volt meter that I'm going to put in once we get back from our trip.


Not only will this give me 2 dedicated USB ports, it will give me an actual voltage readout instead of the current "red/yellow/green" indicator that's built in to the box.

Overall I think this is going to work fine. My previous setup with the Suburban used a 68ah battery and only one time did the battery ever get low enough to trip the low-voltage cutoff on the fridge. For trips of less than 3 days I don't think I even need to worry about recharging the battery, with 1/3 again more power (92ah in the Group 27 FLA.)
 

DaveInDenver

Expedition Leader
Sounds promising Martin. This weekend depending where you're headed you may be more worried about heat than the power your fridge consumes, though. It's sounding like perfect conditions to use my battery-preservation technique of turning it off at night!
 

Martinjmpr

Wiffleball Batter
All right, so the "beta test" was this past weekend. Overall, it worked well. Fridge never lost power and I kept it at 30 - 32 degrees* .

It was a warm weekend (highs in the high 80's) with cool nights (mid to low 50's.) I hooked up the battery when we left the house around noon on Friday.

By late in the afternoon on Saturday, a little over 24 hours later, I was worried that the battery might be low, so to be on the safe side, I put an SAE harness on the box and attached my 100W solar panel output to it (the trailer uses 2 x 6v golf cart batteries with 230ah so it stays pretty well charged for an extended period of time.) The solar controller has a display that supposedly shows State of Charge (SOC) in a % form and it indicated about 48% (I didn't check voltage because it was still connected to the fridge, and I knew it wouldn't give me an accurate "standing" voltage while it had a load on it.)

Since it was so low, I left it connected to the panel. The good news was that it was a nice sunny late Summer day with good, clear sun and by the time the sun went down the SOC was showing over 80%.

At one point I had a 150w inverter attached to the other 12v power outlet to charge a camera battery. That 150w inverter seemed to pull a lot of power from the battery as it seemed to take forever to get the SOC back up.

I set the panel up attached to the battery so it would be facing East in the morning. When I first checked it (around 8:00 AM) it was showing about 62%. By the time we got done with breakfast and were breaking down our camp, it was up to 99% (again, it was a clear, sunny day.) BUT there was no 150w inverter on the battery either, so that may be why it charged up so quickly.

Anyway, the bottom line is that the system seems to work sufficiently. It's not as "elegant" as the dual battery in my Suburban but on the flip side it's "portable" (well, as portable as a 75lb battery can be!)

I still need to get a way to charge the thing up while I'm driving. Two more camping trips this season but I'll have shore power at both of them, so in-vehicle charging isn't as critical. I'll likely bring my plug-in charger to charge the battery up when we are at the campsite. That way I'll have until next Spring to figure out how to charge the box in the truck.

*not sure about other 12v/120v portable refrigerators but on the Indel-B, the temp sensor is at the BOTTOM of the fridge, i.e. the coldest part. So if I want my food to stay <40f for safety, I need to set the thermostat at 30 -32, otherwise the food at the top of the fridge will get too warm.
 
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