how long should a fridge stay cold without recharging - Fiberglass RV


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Old 10-01-2010, 10:04 AM   #1
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how long should a fridge stay cold without recharging

I asked about this in an earlier post but I need clarification and assistance....

I have a fairly new Dometic (Waeco) refrigerator. As soon as I unplug it from AC current and switch to DC on Rv battery power, the fridge will not work very long, maybe four hours. If I hook it back up to the house, the fridge works fine. Shouldn't the refrigerator work for at least 24 hrs. before it needs recharging? The battery isn't old and I just had it tested and recharged. My volt meter reads almost 13 volts when the fridge peters out. Could it be a problem with the refrigerator?

Thanks for advice, Lloyd
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Old 10-01-2010, 12:15 PM   #2
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Floyd, I don't understand electricity well enough to do the calculations but if you have this fridge:
WAECO mobile solutions - Compressor refrigerators
It says it has a 45W power consumption.
Other models can be seen here:
WAECO mobile solutions - Compressor refrigerators

I think that makes it about a 3.75 amp draw which is a fairly heavy load for a battery to maintain. Especially if you have completely drained your battery a few times.
This might help explain batteries:
Frequently Asked Questions (FAQ) - DC Battery Specialists
Here is a tool to calculate run time:
Calculate Battery Amp Hours

From that if you have an 80 amp hour battery you should be able to run 17 hours.
But
You may have partially killed your battery by running it down. Assuming you now have a battery with a 40 amp hour rating, you will only get 8 hours potential run time. If I recall, your fridge might cut out when the voltage drops too low to prevent you from really killing the battery, so the 4 hours does not really seem all that far off.

OTOH, if the fridge is petering out at 13 volts on battery power alone, it might be the protection circuitry in the fridge or other controllers.

Maybe Peterh or someone more knowledgable might pipe in.
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Old 10-01-2010, 12:25 PM   #3
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Batteries to lose amp hour cpapacity over time, yet will still read 12-13 volts. voltage is simply the energy potential betwen the lead and zinc plates and the acid between.

Even though a battery will out put 12V nominal, the actual draw supported by it can be reduced if a cel or two go bad. to eb sure take the battery to a reputable dealer who can do a proper load test on it and tell you the condition.

Age vibration and temperature extreams all can shorten and batteris life quite quickly.
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Old 10-01-2010, 12:58 PM   #4
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thank you so much....The battery I have is 18 months old and has been run down a few times, although it takes a full charge. I probably weakened it since then. I think I will start from scratch with a new battery and leave it on a battery tender (trickle charger) while I'm not using it. I will read about batteries on this website for more knowledge. Thanks again.
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Old 10-01-2010, 02:05 PM   #5
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Edited to add: Your thread title asks how long a refrigerator should stay cold without re-charging, but I'm thinking you mean "how long should the batteries keep it running for," right? Staying cold without running would have more to do with insulation.

***************

For the "house bank" in boating, we try to not run batteries down past the 50% point. That's because they have a much longer (overall) life this way. So, as Roy was speaking of above, what you can do is calculate your load(s) in amp hours, and compare that to what you have in battery capacity.

I think you would have to have either a pretty hefty battery bank OR a pretty strong re-charging source(s) to run your refrigerator on it for 24 hours (especially continuously). For example, on a boat it might not be uncommon to have a multiple battery bank of, say, 300 amp hours capacity, AND a solar panel or wind generator to keep them charged. Refrigeration is one of the biggest loads, and people with smaller battery banks and/or fewer ways to keep them charged oftentimes choose (or need) to have an icebox instead of a refrigerator. Refrigerators are getting more efficient, but they are still a good-sized power draw.

(By the way, in case you are wondering, I'll add that few people on boats have propane refrigerators, because it is not safe to have a pilot light running on a boat - I won't bore you with the details, but I thought my comments might not make sense unless you knew that boaters didn't commonly use 3-way refrigerators.)

All this to say that I'm not surprised that you would have a problem running your refrigerator on only your battery bank, without any recharging going on, for 24 hours.

If you know you want to be able to do that, I would start with calculating the load/draw of your refrigerator, and then "work backwards" to figure out what you need in the way of battery capacity and/or recharging capability.

Raya

PS: And, as was mentioned, by the time your battery(ies) get down to 12v, they are pretty low --- although that seems weird when you hear them described as "12 volt batteries."
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Old 10-01-2010, 03:51 PM   #6
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[QUOTE=lloyd cicetti;225371] I think I will start from scratch with a new battery ... I will read about batteries on this website for more knowledge. [QUOTE]

Lloyd,
Do the research before you buy a new battery. Based on what it seems you want or need, you might want consider a dual 6V deep cell set up.
Then add the solar to match. Ramsond on ebay has some pretty good deals. The panels can be had for $3 / watt. PM me for info.
Roy

PS, Raya has given you some good info. I was trying to find a link to battery info posted here via a link about the usable or magical "1 volt" in battery systems but have not found it yet. I was dumbfounded about batteries until I read it. Sorry I can't explain it, but finally understand it so it makes sense to me.
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Old 10-01-2010, 04:18 PM   #7
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About a year ago I decided I was going to buy a new 13' trailer. I really liked the Trillium but could not get it with a 3 way refrigerator.
Unless you stay in a campground with electrical hookups you're very limited when you rely on electricity for refrigeration in your TT unless you go the the added expense and weight of multiple batteries and a high wattage solar array.
My problem was resolved when I found a well cared for, fairly late model 16'
Scamp.
John
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Old 10-01-2010, 04:36 PM   #8
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A good source of technical information for RVs & trailers is Mark Nemeth's RV Technical Articles. There are two pages of information on the care & feeding of 12V batteries: The 12 Volt Side of Life, Part 1 and The 12 Volt Side of Life, Part 2.
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Old 10-04-2010, 07:45 PM   #9
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Dometic Refrigerator

Quote:
Originally Posted by lloyd cicetti View Post
I asked about this in an earlier post but I need clarification and assistance....

I have a fairly new Dometic (Waeco) refrigerator. As soon as I unplug it from AC current and switch to DC on Rv battery power, the fridge will not work very long, maybe four hours. If I hook it back up to the house, the fridge works fine. Shouldn't the refrigerator work for at least 24 hrs. before it needs recharging? The battery isn't old and I just had it tested and recharged. My volt meter reads almost 13 volts when the fridge peters out. Could it be a problem with the refrigerator?

Thanks for advice, Lloyd
Hi, Lloyd

I would like you to clarify a couple of things, please. You say "the fridge will not work very long, maybe four hours." Do you mean that it stops cooling and starts to warm up? If this is the problem then the switch to DC may be a problem. Are you sure the fridge is getting DC to the cooling unit?
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Old 10-05-2010, 07:31 AM   #10
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Lloyd, I think you are asking too much of your house battery. The 12v function is supposed to be powered by a running tow vehicle's alternator.

To add to Raya's comment, most boats I have sailed have had 12v fridges, but they are ONLY powered when one of the engines is running. These are sail boats, so you have to remember to start one of the engines for a few hours a day to keep the fridge cool. These are $600,000 boats, and they don't even attempt to run the fridge on the house batteries. There are different setups, and some people who are spending a lot of time on their boats may opt for a battery operated system with a larger battery bank and/or solar or wind generator.

I don't think you are going to be happy with your fridge's performance when running on the house battery. You are going to seriously reduce the lifespan of your battery, and won't get the run-time that you are hoping for without adding batteries to the bank. Another thing to consider is that the "12v" fridge is really designed to run on alternator voltage, which is more like 14.5 volts. A battery which is not in a state of charge will be putting out closer to 12v. Your fridge may have a low voltage monitor that cuts out the power under these conditions in order to save the tow vehicle battery (not in your case, but this is what they assume you are doing).
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Old 10-05-2010, 03:11 PM   #11
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Originally Posted by mcbrew View Post
Lloyd, I think you are asking too much of your house battery. The 12v function is supposed to be powered by a running tow vehicle's alternator.

To add to Raya's comment, most boats I have sailed have had 12v fridges, but they are ONLY powered when one of the engines is running. These are sail boats, so you have to remember to start one of the engines for a few hours a day to keep the fridge cool. These are $600,000 boats, and they don't even attempt to run the fridge on the house batteries. There are different setups, and some people who are spending a lot of time on their boats may opt for a battery operated system with a larger battery bank and/or solar or wind generator.

I don't think you are going to be happy with your fridge's performance when running on the house battery. You are going to seriously reduce the lifespan of your battery, and won't get the run-time that you are hoping for without adding batteries to the bank. Another thing to consider is that the "12v" fridge is really designed to run on alternator voltage, which is more like 14.5 volts. A battery which is not in a state of charge will be putting out closer to 12v. Your fridge may have a low voltage monitor that cuts out the power under these conditions in order to save the tow vehicle battery (not in your case, but this is what they assume you are doing).
Oops... I didn't see that you have a compressor-type fridge. Does the manufacturer recommend using it on batteries that are not actively being charged? The boat fridges I am used to, as mentioned, are not supposed to be run off of the battery bank, but rather the alternator. Have you talked to Dometic about this issue?
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Old 10-06-2010, 12:47 AM   #12
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There are a number of 12-volt boat refrigeration systems now that are not engine driven and/or do not require the alternator to run. I have friends with 12-volt systems who run them off a couple of solar panels and a battery bank and do not need to charge with engine/generator. They've gotten quite a bit more efficient recently.

That said, they are still a substantial, relentless draw, and no-one is running them off one or two group 24 or 31 batteries, like you'd have in a camper, and with no solar or wind generation capabilities. They still draw too much for that.

Also, sailors (and, I'm sure, campers who are boondocking) are actively managing their energy budget, and are often using relatively sophisticated battery monitors. They are constantly aware of what's going in and out of the batteries. That's not to say it's super difficult, or they are so special, but just that it is an overall mindset.

Raya
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