Fridge Use on Batteries Only

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jkhenderson

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Aug 10, 2019
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9
I’m interested in learning about how long I could expect to run my residential refrigerator on twin 12V batteries. Obviously, I could just experiment, but I’d like to have a good idea of what to expect before doing so. If I installed and connected the batteries the night before bringing the RV to my home to load up gear and food, can I expect the batteries to last through the night… say, 12 hours, or would they likely discharge before that length of time? I’m unable to park my RV at my home over-night due to local ordinances. But I’d love to have the refrigerator already cold in the morning to be able to load up and leave earlier in the day. In a perfect scenario, I could connect just one of the batteries to run the refrigerator, then have the second battery for keeping the refrigerator cold while traveling to my destination. I’m not yet familiar with how much charging of the batteries takes place while I’m driving (if any at all)?
 

Dreamsend

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Aug 16, 2016
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Depends on how many amp hours of juice your batteries have (to 50% state of charge) and how many amps the fridge will use in 12 hours or until you can supply a charge or hook up. I'd look at the fridge specs and find out the power draw, and assume it's gonna run most of the time when first loaded. (don't forget to convert 12V to 120 V) And add in the 10% inverter loss also. You could at least estimate and see if you even come close. Do this in your 1 battery scenario to check feasibility as well.

Folks here have suggested making sure anything you put in the RV fridge and freezer are already cold and/or frozen before loading up. Others will likely be along with some real numbers but it will still depend on your battery capacity and your fridge power draw.
 

RRR

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May 20, 2018
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Beaverton, Oregon
I may be comparing oranges to grapes but maybe give you an idea.

I have four 6v deep cycle Costco batteries. When the wife goes to do her Indian outreach mission at the local casino in mild weather I need to run the generator in the AM for a few hours. This is the front heat set to 60° minimum lights, some TV, Internet hotspot and laptop charging.

Most of the time we grab our few rags and essentials, food and go to the storage lot and load and go. The residential fridge cools fast enough I don't worry about it.

I think with two deep cycle batteries that you should get several hours of run time from the refer.
 

Ex-Calif

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May 15, 2020
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Your avatar looks like you have a 5W?

When you say residential fridge do you mean a house fridge or an RV fridge? I reckon on two batteries an RV fridge would last <10 hours and if a residential fridge probably <5-6 hours.

I would not advise hitting the road with dead batteries. Repeated deep discharging of the batteries will definitely shorten battery life as well.

Whether the truck alternator charges the batteries under way depends on the rig but I assume it will. I would load all my refrigerator items in a big cooler and transport them when I pick up the rig.
 

Larry N.

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May 26, 2010
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Westminster, Colorado
Don't forget that anything else in your rig that uses DC power will also be draining the batteries. My Ventana came with a residential fridge (as opposed to an RV fridge, Dan) and came with a bank of 8 6V batteries (large, golf cart type). I make it fine through the night, and could run a bit longer, though not ALL day long. After a night (roughly 10 PM to 7 AM) it takes 3-4 hours for my generator to bring them back to full charge.

Of course there the small LED aisle lighting in the bedroom, the dash radio, the furnace fans (generally this is 30-50º at night for this timing; my Oasis hydronic heating runs on diesel fuel), microwave in standby, alarm clock, and sometimes a small tabletop fan running also, plus whatever overhead the inverter uses in converter the 12V DC to 120 V AC. There are probably some things I'm not thinking of right now, also.

So, depending on the load your rig uses, you might want another pair of batteries, and more if the furnace runs very much. On a warm night with care in what actually runs you might make it, but I'd take Linda's advice and check the specs on the fridge, the batteries, and anything else that might run through the night and do the math.

Finally, as others have mentioned above, don't allow the batteries to run too low. The 50% charge is a good target for the max allowed, but it's not a magical one second it's OK the next it's dead, rather try not to let it get very much below that 50%, and especially not very often below that.
 

whiteva

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Feb 15, 2012
Posts
459
Location
North Florida
I have just completed changing from Norcold to a residential fridge with a inverter. I plan on running several tests this week to determine battery hours and draw down. (We have a trip planned in a couple of weeks so I will load the usual items in the fridge)
I will reply to the group with my findings. (don't ya just love an engineer with a screwdriver, pliers and a spreadsheet full of data)
 

John From Detroit

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Apr 12, 2005
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25,115
Location
Davison Michigan
How long can you run a resendtal fridge on twin 12 volt batteries. NOT ENOUGH INFORMATRION.. I will explain why.

Group 24 MARINE/deep cycle, abou 75 AH each 150 total of that you can use about 30 perhaps 40 tops. Residential fridge 100-400 watts will use 250. that's 25 amps at 12 volts by the time you factor in loss. and then there is the Peukert's Law which states you won't get nearly the full capacity at that rate so make it 30 minutes.

Group 27 and 28 are either side of 100 amp hours each so perhaps 45 minutes
Group 31 at 130 amp hours each. might go a bit over an hour

Size 4D or 8D at around 230 and if DEEP CYCLE... 8-10 hours. half that for MARINE/deep cycle

I do not recommend trying it.
 

Mark_K5LXP

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Nov 17, 2018
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Albuquerque, NM
Telling someone what to expect when we don't know any of his system particulars isn't helping him. Once he relays what equipment he has would be a start, if he were to make a few basic operating measurements the run time can be estimated with a pretty high degree of accuracy. Let the data drive the solution, not arm waving based on assumptions or arbitrary limitations.

Specifically- what's the draw of the refrigerator. If not measured, per the unit spec's. Knowing what the average power is once it reaches temp would be useful but it can be estimated;

Any other loads present;

The battery compliment. Rated Ah would be assumed but if there's a measured capacity that would be better.

One way to get empirical data fairly easily would be to run the expected loads for a short period of time, say a few hours. Note the Ah used and DOD and from there longer run times can be extrapolated.

Mark B.
Albuquerque, NM
 

Matt_C

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Mar 4, 2019
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479
Location
SE - Mich
We really do need more information. Both about the reefer and the house bank.

This can be done (I hope, as we have been doing it for about 12 years now. It is not a full size reefer, and we can keep the House Bank good for about a day and an half at a July music festival. That is on a pair of good GC2s, now T105s.
Matt
 

creativepart

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Jul 6, 2014
Posts
42
Location
Hill Country, TX
We can't answer your question - but I can tell you that my residential fridge will run 8 to 10 hours on 4-100ah AGM batteries IF the batteries are charged 95% or better and I will have about 65% state of charge the next morning.

Sounds like you have half of that battery storage so, perhaps you could get 5 to 6 hours?

I recommend that before you try this or any other battery test that you install a shunt-based battery monitor to know the actual state of charge of your battery bank. Voltage based meters are unreliable for this kind of test.

 

Oldgator73

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Dec 28, 2017
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Why does the fridge have to be on the night before you leave? Can’t you turn it on like 2 hours prior to departure and just before you take off load it?
 

Utclmjmpr

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Sep 14, 2009
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Cedar City, UT
Most refers take many more than two hours to get down to set level,, if you load non cooled food into it with out a prior cool down period it will take much much longer that if you had pre-cooled it..>>>Dan
 

Oldgator73

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Dec 28, 2017
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Most refers take many more than two hours to get down to set level,, if you load non cooled food into it with out a prior cool down period it will take much much longer that if you had pre-cooled it..>>>Dan
Why would you load room temp food in the fridge? I would freeze everything that is freezable except what you plan for dinner that evening. Freeze several gallon jugs of water and put them in the fridge when you turn it on. This ain’t rocket science. All you are doing is removing the heat (BTU’s) from the fridge to someplace else.
 

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