How is everyone powering their portable fridges?

[4x4junkie]

Not to burst anyone's bubble but in the RV world 12.8 is the steady state after the battery rests for 2-3 hours for AGM and wet cell is 12.6 for 100% charge. You should never check the battery state immediately after charging.

It does depend on the battery.

I've measured over 13.0 OCV on my Deka Marine Master #DP27 batteries a full day after charging them (using my Fluke 87 DMM). After two weeks of sitting they might drift down to somewhere within the 12.9V range.
A mere 2-3 hours after charging they'll likely still be at 13.4 or more volts... this is not enough time for an accurate voltage (SoC) measurement after charging.

The Deka DP27 is a flooded type that uses lead-calcium a.k.a. "maintenance-free" grids (same type used in AGMs), which makes the wet-cell numbers on that chart that much more in error, since it doesn't specify what type of battery it's for.

 

[bearman512]

You are right 4x4junkie. You really should not test the battery for at least 4-12 hours of resting with nothing attached. I should of said that this is a good reference chart if all you have is a cheap digital gauge similar to what you see in RV's or the $5 Harbor Freight.
I am not trying to be argumentative but after contacting 3 seperate Solar companies they all stated 12.7 is 100% on any AGM they have installed and 12.65 is for any wet cell deep cycle.
I think the internet does have the most inclusive SoC charts available and none of them show a SoC over 12.65.https://www.google.com/search?q=agm+battery+state+of+charge+table&safe=active&espv=2&biw=1908&bih=924&tbm=isch&tbo=u&source=univ&sa=X&ved=0ahUKEwjam9m3otfMAhXH1IMKHb3RBIEQsAQIPQ&dpr=1
I have a Deka DC31DT in my camper and the only time it reads 13.1 is if there is no direct sunlight on the solar panels or the panel or the controller goes to float.

 

[luthj]

Open cell voltages will vary with battery age a bit. Additionally they vary with temperature. Unless we are all checking similarly aged batteries at the same temperature, there will be differences.

The best way to ensure a lead acid battery is fully charged is to monitor its return amps (Charging amps) at a specific voltage. Usually this is the absorb voltage, and return amps is specified by the manufacturer for 100% SOC. For my lifeline bank the return current at 100% SOC (with temperature adjusted absorb voltage) is 0.5A per 100AH of capacity.

Also, a load of even a few amps will make any voltage measurements inaccurate. The best option is a shunt type battery monitor. Properly setup, they will provide accurate measurements of SOC. For most systems, its worth the 180$.

Anyways. Solar is the best way to power a fridge for more than a day or two. Regardless if its portable or not. A DC-DC charger from the alternator works if you drive enough. Sterling and Ctek make some good units.

 

[4x4junkie]

You are right 4x4junkie. You really should not test the battery for at least 4-12 hours of resting with nothing attached. I should of said that this is a good reference chart if all you have is a cheap digital gauge similar to what you see in RV's or the $5 Harbor Freight.
I am not trying to be argumentative but after contacting 3 seperate Solar companies they all stated 12.7 is 100% on any AGM they have installed and 12.65 is for any wet cell deep cycle.
I think the internet does have the most inclusive SoC charts available and none of them show a SoC over 12.65.https://www.google.com/search?q=agm+battery+state+of+charge+table&safe=active&espv=2&biw=1908&bih=924&tbm=isch&tbo=u&source=univ&sa=X&ved=0ahUKEwjam9m3otfMAhXH1IMKHb3RBIEQsAQIPQ&dpr=1
I have a Deka DC31DT in my camper and the only time it reads 13.1 is if there is no direct sunlight on the solar panels or the panel or the controller goes to float.

Some charts must be running behind current state of battery technology then... because my DP27 Dekas will sit at 13 volts OCV for days after charging.

After a night of camping, which includes running a bunch of LED lights and the stereo for several hours, and of course the fridge cycling all night, I might see mid-high-12.7s in the morning before the sun is up. Obviously at this point the batteries wouldn't be at 100% SoC, but probably closer to around 80%. I've seen very similar on Optima AGMs too, which is supported by Duckys Dad's post.

Your Deka DC31DT does not have lead-calcium grids (it is a "low-maintenance" unit with lead-antimony grids), so that would be why you aren't seeing as high of voltage on yours.

This page has decent charts that show differences between voltages of the two common grid types (and does state in the text OCVs may be as high as 13.1V on calcium-grid (Ca/Ca) batteries):
http://jgdarden.com/batteryfaq/carfaq4.htm

 

[QPDO]

So I've purchased the 50qt ARB fridge with travel bag and the largest and highest capacity deep cycle battery that would fit into the stock tray of my 2013 Jeep JKU. The odyssey 34R-PC1500. Which boasts 850CCA, 68Ah and a reserve capacity of 135min. I don't imagine the Jeep will sit idle for much longer than 12hrs, but in case it is... would anyone be able to shed some light on how long I could run the fridge without impacting the starting ability? Average temperatures will be about 75 degrees Fahrenheit or 23 degrees Celsius. I've been trying to find calculators... but it all seems rather vague. So some real life experience would be appreciated!

 

[4x4junkie]

There really is no good way to pin down how long a fridge will run under typical outdoor conditions before depleting a battery because there are just too many variables involved (and is likely why you haven't found much info on it).

I've gone 5 days straight w/o issue with my Edgestar fridge and dual batteries, temps were about 75°F by day, and maybe 40°F at night. Other times when temps were 100°F day and 75°F night I would start to see my batteries dip below 12V after only two days. So you can see the variability of it.

If you won't be sitting for more than 12 hours at a time, then you'll probably be OK in the vast majority of conditions (plus the fridge has a low-voltage cutoff that should kick in before the battery gets to a point it cannot start the engine). Maybe adding a 2nd (parallel) battery to increase your Ah capacity can help too if you can find a place to mount it.

 

[Vanaroo]

I am not trying to be argumentative but after contacting 3 seperate Solar companies they all stated 12.7 is 100% on any AGM they have installed

I don't know what AGM's those three companies have installed, but one brand that is generally well thought of is Lifeline and their specifications say the following for charge state (SOC) of their 12-volt battery at open circuit voltage (resting for a minimum of four hours with no charging or load) (this is on page 30 of their 38-page battery manual which has quite a bit of good information):

12.8 or greater = 100% SOC (I have a Lifeline battery bank and will sometimes see 12.9 or greater resting at full charge)
12.5 = 75%
12.2 = 50%
11.9 = 25%
11.6 or less = 0%

I like to buy batteries from a company that publishes these sorts of specs (along with specific charging info/storage info/etc.) just because then I can look them up directly vs. relying on varying people at solar companies, etc. Good to have for future reference as well when caring for the battery bank. Here's a link to the Lifeline manual (last updated April 2014):

http://lifelineb.wpengine.com/wp-content/uploads/2015/12/manual.pdf

 

[Vanaroo]

So I've purchased the 50qt ARB fridge ... would anyone be able to shed some light on how long I could run the fridge without impacting the starting ability?

Maybe it's because my background is boats, but I'm used to the starting battery being "sacred," and reserved for starting only. I suppose I might fudge a bit with a land vehicle, especially if it had a clutch (pop start) and/or I had a couple of jump packs (and wasn't going to be anyplace too remote). But likely not. Even if the start battery was not dragged down to a no-start condition, it would still be hard on it to be discharged deeply on a regular basis (it's hard on a deep cycle battery and they are meant for it). Plus you'd have no way of knowing (since no battery monitor).

I rigged up a setup for a friend's car a few months ago that consisted of a 100-watt solar panel on the roof rack (overkill, but he had a spare panel), and then a small box with a Lifeline U-1 battery and MRBF (possibly underkill on battery size but he thought a Group 24 would be too physically large although it turned out it would have been fine), a Victron 75/15 solar controller, and two 12-volt "cigarette" outlets (also fused). One of those was for a Dometic 40 liter refrigerator and the other just for whatever. This has worked great and was pretty simple to set up. If there is ever a situation where there is a lack of sun for many days, the fridge would be turned off (due to smallish battery bank) but it's fine for an overnight or maybe two in cool weather (he hangs in sunny climates). There is also the option to plug it into the car's cigarette outlets when underway. He made a conscious choice not to connect the two banks with a switch or automatic relay (because he had the solar panel and controller already, so just needed to buy a battery and voila!), but that would have been an option. As it is the refrigerator/"house" system is simple and stand-alone -- and can't touch the car's start/native electrical system (yet allows him to take advantage of alternator power by simply plugging the refrigerator into the car's native cigarette lighter if desired when traveling [say if traveling on a string of rainy days]).

We did some tests (plus I run a Dometic 50 liter 24/7 and so already had some idea of power use) and the Dometic 40 is using something like 12-15 amp hours overnight in warm but not ridiculously hot conditions. Of course this is only when the sun is down, so the car is not "greenhouse hot." And when it IS greenhouse hot, the solar panel is active. IIRC the U-1 has 35 amp hours, so it's close but still okay (as mentioned, he would go with Group 24 if doing again most likely).

The box is quite small and fits in the rear passenger seat footwell up against the center hump (still room for feet on an ocassional basis). I realize you may not want to go that way specifically, but I would be uncomfortable using the start battery for anything but very occasional use (say when running errands you buy ice cream and then leave the fridge on while you do some other tasks that same afternoon, then drive more).

 

[subdewd]

So I've purchased the 50qt ARB fridge with travel bag and the largest and highest capacity deep cycle battery that would fit into the stock tray of my 2013 Jeep JKU. The odyssey 34R-PC1500. Which boasts 850CCA, 68Ah and a reserve capacity of 135min. I don't imagine the Jeep will sit idle for much longer than 12hrs, but in case it is... would anyone be able to shed some light on how long I could run the fridge without impacting the starting ability? Average temperatures will be about 75 degrees Fahrenheit or 23 degrees Celsius. I've been trying to find calculators... but it all seems rather vague. So some real life experience would be appreciated!

The ARB has the low-voltage shut off that you can set at low-med-hi in order to protect yourself from draining your 12V power source too low. If you have a cover/bag (like the picture shows) that reportedly helps a bit with insulation and will help minimize run time for the fridge. Another thing to remember is that if you park your Jeep and keep it closed up in the sun, inside may be higher/hotter than out...again impacting run times for the fridge.
I have the same fridge for almost 3 years and love it! I've since gone to a dual battery setup with a Grape Solar 100 watt flexible panel on top to keep it going worry free!

 

[plh]

The ARB highest voltage setting for cut-off is 11.8 VDC IIRC. Makes it pretty rough on your battery to continuously rely on this feature to manage your SOC. High 11.8. Med 11.4. Low 10.1 (good golly - WHY?).

 

[luthj]

The issue you are going to run into using only the alternator for charging is that it is not designed to charge a deeply discharged battery. The result is chronically undercharged battery which will not last long.

The other issue is accidental over discharge resulting in a no start situation. If you have other means to jump start the car this is less of an issue.

The best setup is a second battery with isolaton relay. Follow up with an occasional full charge from a good quality 120v charger or small solar panel for improved battery life. Just buying cheap deep cycle battery and replacing it every year may be a viable option as well.

 

[Vanaroo]

The ARB highest voltage setting for cut-off is 11.8 VDC IIRC. Makes it pretty rough on your battery to continuously rely on this feature to manage your SOC. High 11.8. Med 11.4. Low 10.1 (good golly - WHY?).

I've wondered the same thing. I mean, even 11.8 is basically saying "you've just ruined your battery - figured you might want to know." For my house battery 11.8 is is around 75% discharged. Ouch. 11.6 is 100% discharged (buh-bye), and 10.1? Can you be 115% discharged? Maybe the average starting battery is tougher (I don't deep cycle those, so not as familiar with their deep cycling behavior), but it bugs me that having that cut-off sort of implies it's going to protect your battery(s). I know it would not protect my particular house batteries.

 

[4x4junkie]

The ARB highest voltage setting for cut-off is 11.8 VDC IIRC. Makes it pretty rough on your battery to continuously rely on this feature to manage your SOC. High 11.8. Med 11.4. Low 10.1 (good golly - WHY?).

I've wondered the same thing. I mean, even 11.8 is basically saying "you've just ruined your battery - figured you might want to know." For my house battery 11.8 is is around 75% discharged. Ouch. 11.6 is 100% discharged (buh-bye), and 10.1? Can you be 115% discharged? Maybe the average starting battery is tougher (I don't deep cycle those, so not as familiar with their deep cycling behavior), but it bugs me that having that cut-off sort of implies it's going to protect your battery(s). I know it would not protect my particular house batteries.

Unless you have your fridge's power hardwired directly to your battery with 6-inch long pieces of #10 wire, 11.8V is a very acceptable cutoff voltage. I'm sure it was ARB just accommodating the 0.5-1.5V drop in the wiring of the average user installation.

(my Edgestar cuts out at 10.8V, yet when I found the LVC triggered one time I measured the battery, it was standing at 11.9V)

 

[Vanaroo]

Unless you have your fridge's power hardwired directly to your battery with 6-inch long pieces of #10 wire, 11.8V is a very acceptable cutoff voltage. I'm sure it was ARB just accommodating the 0.5-1.5V drop in the wiring of the average user installation.

(my Edgestar cuts out at 10.8V, yet when I found the LVC triggered one time I measured the battery, it was standing at 11.9V)

I'm not sure I understand your post here. I have my fridge wired for as little voltage drop as possible, because I've read that the Danfoss compressor electronics will live a lot longer if they don't have to suffer voltage drop. But are you saying that the refrigerator's low voltage cutoff, counts on voltage drop, thus if it cuts off at 10.8 volts, they "know" you will have wired it for a hefty voltage drop, so then really your batteries will be at 11.9 volts and all will be fine? It sounds like that works well for your setup, but it wouldn't work all that well for mine (I don't have that much voltage drop, plus my batteries would be too far discharged even at 11.9 volts). I don't rely on the refrigerator voltage cutoff for battery management, so I was just responding to poster "plh" as I share the same opinion.

There are lots of ways to do it and my feeling is that as long as a person understands what's going on, and can thus make choices that suit them, all is good. I just was thinking of the person who would assume the refrigerator's low voltage cutoff would keep their batteries safe, without realizing that something like 11 volts is really going to shorten their life. No-one likes expensive battery surprises.

 

[4x4junkie]

No, that is not what I said.

There are two things that need to be accounted for when determining the trigger voltage of a LVC:

1.
The voltage drop in the complete wiring circuit... Even in the best of fridge installations this will usually be 0.2-0.3V, and more typically is about 0.4-0.6V (with a cig-lighter connection, 1.0-1.5V is common).

2. The voltage of a battery while under load vs. that while resting (SoC readings are always taken after a battery has been at rest for a bit). The difference between these readings on a healthy 100Ah battery is about 0.2V while under the 4-5 amp load of a fridge (and increases as SoC decreases).

So in a case of having 0.3V drop in your wiring, plus the 0.2V drop of your battery while under load, a LVC set to 11.8V would cut out right at approx 50% SoC (12.3V battery resting voltage). That about matches dead-on the advice that is frequently given about how far you should discharge a lead-acid battery (it should also be noted that this is not a hard-fast rule, an occasional discharge below 50% does NOT ruin a battery, it is just something that you should try not to make a regular habit of is all... If your fridge LVC is cutting out on a regular basis, then you have other issues with your setup that need addressing).

Many (most?) installations have more than 0.3V drop in them, so that is why ARB also provided the 11.4V & 10.1V settings.