Dometic Fridge on 12 Volt while towing - Fiberglass RV


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Old 08-05-2020, 07:39 PM   #1
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Name: Eva and Kirk
Trailer: Casita 17 Spirit Deluxe
Virginia
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Dometic Fridge on 12 Volt while towing

I have looked at past posts regarding this issue in the forum. There is some disagreement regarding running the Dometic fridge on 12 volt while towing. The issue comes down to whether or not the tow vehicle alternator can keep up with the load of the fridge as well as the normal load of the tow vehicle electrical system. There are also remarks that indicate that it might work if only the towing harness is wired with #10 wire (nobody does that).
No doubt this will vary by tow vehicle. In our case we have a 2007 Dodge Dakota pulling a Casita 17 Spirit Deluxe. It seems to me that if I put the fridge on 12 volt, check the battery voltage, then start the fridge and again look at the battery voltage while the tow vehicle is hooked up and running I should be able to confirm if the battery is charging or draining by looking at the battery voltage using the monitor we bought that plugs into the 12 Volt receptacle. However, Iím not sure what voltage to look for.

It seems to me that any voltage above 12.65 volts for a fully charged lead acid battery should indicate Iím ahead of the game instead of falling behind. Has anyone else looked at this?

We are traveling to PA from VA in a week and a half and I donít want to be sitting beside the road with a dead tow vehicle battery because the fridge pulled it down. On the other hand, what good is 12V if you canít run the fridge while towing? Boondocking I can see how it would drag the house battery down in a matter of hours. Then it would be propane or nothing. But towing? Like I said, if I canít run it while towing, whatís it even good for?
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Old 08-05-2020, 07:53 PM   #2
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Your TV battery should be fine. It's close to the alternator and has adequate wiring. The problem will be draining the trailer battery. If it's at 13V with the fridge on and the TV running, you're not drawing it down and may be charging slightly. As far as draining the TV battery while camping, you should either unplug or have a relay installed. If boondocking, run the fridge on propane. Running on 12V will take all the trailer battery's useful power in 5 hours.
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Old 08-05-2020, 08:28 PM   #3
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Quote:
Originally Posted by Evirk View Post
I have looked at past posts regarding this issue in the forum. There is some disagreement regarding running the Dometic fridge on 12 volt while towing. The issue comes down to whether or not the tow vehicle alternator can keep up with the load of the fridge as well as the normal load of the tow vehicle electrical system. There are also remarks that indicate that it might work if only the towing harness is wired with #10 wire (nobody does that).
No doubt this will vary by tow vehicle. In our case we have a 2007 Dodge Dakota pulling a Casita 17 Spirit Deluxe. It seems to me that if I put the fridge on 12 volt, check the battery voltage, then start the fridge and again look at the battery voltage while the tow vehicle is hooked up and running I should be able to confirm if the battery is charging or draining by looking at the battery voltage using the monitor we bought that plugs into the 12 Volt receptacle. However, I’m not sure what voltage to look for.

It seems to me that any voltage above 12.65 volts for a fully charged lead acid battery should indicate I’m ahead of the game instead of falling behind. Has anyone else looked at this?

We are traveling to PA from VA in a week and a half and I don’t want to be sitting beside the road with a dead tow vehicle battery because the fridge pulled it down. On the other hand, what good is 12V if you can’t run the fridge while towing? Boondocking I can see how it would drag the house battery down in a matter of hours. Then it would be propane or nothing. But towing? Like I said, if I can’t run it while towing, what’s it even good for?
Voltage loss occurs along each part of a circuit. The only thing that matters is the total voltage loss through the entire circuit. It might be that you can provide a heavy gauge wire from the tow vehicle's battery to the 7-pin, and then operate with the trailer's original wiring from there. The total sum of the circuit's losses just have to provide no more than the critical sum of resistance which will lower the voltage below the required target minimum.

It does seem that the simple test is to check the trailer's battery beforehand, then apply the load (the refrigerator) and see if there's a drop or an increase in the voltage as measured at the trailer's battery.

However, I'll offer a caution. I always knew when I bumped the 12VDC switch on our refrigerator in the Casita because the fan in the load center would immediately switch on and run continuously. This was with the tow vehicle unconnected. But, I think it would even happen on shore power as best I recall; it's been a while, so I don't recall precisely.

So it's pulling a significant load relative to the load center's capacities even when it's just operating off the trailer's battery. The 12-volt element appears to be 175 watts on the RM2454 Dometic Americana if that's what you have; nearly 15 amps.

https://www.yumpu.com/en/document/re...service-manual

The other issue to be aware of is in Section 5.1 that Dometic notes that operation on 12 volts provides a "holding mode, not a full cooling mode". So, in the end, the best you will do is to accomplish limited cooling.

I say give it a whirl to see what you learn and whether it might meet your needs.

As far as what they are good for, absorption refrigerators provide a great subject for endless navel-gazing on forums like this.

They also serve to cool your food under some but not all circumstances.
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Old 08-06-2020, 07:54 AM   #4
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Mikes got it right. These fridges do a much better job of taking up forum space for trouble shooting and philosophy than actual food preservation, but they do actually occasionally cool food.

And Lynn is right. Assuming your truck system is working anything like it should be, that’s not the battery you need to worry about. What would cause issues is if the trailer was still drawing from the truck battery after you turned the truck off, and kept the fridge in 12v mode. Unless things are somehow rigged electronically, this won’t happen.

I learned how much of a power hog these fridges are when I had a motorhome, and would leave it on 12v while I was traveling, not just driving. So it would stay on 12v while I stopped for lunch, went for a short hike etc. That’ll kill the coach battery fast.

So yeah, monitor the trailer battery while hooked up, not the truck battery.
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Old 08-06-2020, 08:14 AM   #5
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When we got our first trailer and I was naive and uneducated I tried running our refrigerator on 12 VDC . Arriving at my destination with my trailer battery badly discharged after driving all day said to me “ This just ain’t working”
Being stubborn , I read up on how to make 12VDC work .I soon figured out that rewiring my truck , rewiring my trailer , rewiring my refrigerator. buying another battery , buying a DC to DC converter . , buying a fancy battery monitor and buying God knows what else just wasn’t worth the time , effort or cost .
I run my refrigerator on propane when traveling , it’s easy to do and works well
You can make almost anything work if your willing to devote enough time ,energy and money but at some point common sense has to win out .
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Old 08-06-2020, 09:59 AM   #6
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I generally allow the refrigerator to run on shore power for a day or two prior to leaving. I'll put food in the fridge the morning of departure, then turn it off during travel. When I arrive at my destination, I get the fridge running again (on propane or shore power) and haven't had a problem. Granted, my travel times are generally in the 3-5 hour range.
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Old 08-06-2020, 10:05 AM   #7
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Originally Posted by steve dunham View Post
When we got our first trailer and I was naive and uneducated I tried running our refrigerator on 12 VDC . Arriving at my destination with my trailer battery badly discharged after driving all day said to me ď This just ainít workingĒ
Being stubborn , I read up on how to make 12VDC work .I soon figured out that rewiring my truck , rewiring my trailer , rewiring my refrigerator. buying another battery , buying a DC to DC converter . , buying a fancy battery monitor and buying God knows what else just wasnít worth the time , effort or cost .
I run my refrigerator on propane when traveling , itís easy to do and works well
You can make almost anything work if your willing to devote enough time ,energy and money but at some point common sense has to win out .
Lots of folks do run on LP while travelling. A large number of the newer absorption RV fridges don't even have a 12V option - just 120V and LP. For a short run (hour or two) just leaving it off - if it's well insulated, and it isn't overly hot out - you can still be in good shape, but anything longer than that and I found (especially in the summer heat) that you ended up tossing a lot of food by the time you reached your destination 5 or 6 hours later. I have no problem running it on LP while travelling.
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Old 08-06-2020, 10:06 AM   #8
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I own a '99 Nissan Frontier 4 cyl Manual shift pickup. For TEN years, I have pulled a 13' Scamp with the small 1.9 cu ft Dometic Fridge on 12v. NEVER, have I had an issue and have- like some others- stopped to eat, get gas etc and leave it on. I do have an onboard battery.
One thing I will note here, I did install my own 7-pin and ran the 10ga wire from the battery (with a breaker) to the 7-pin Hopkins on the rear. So, the bottom line is for me, I know I'm getting enough amps back there obviously to keep it running.

No, I did not install an oversized alternator on my Nissan. I'm stilling running the "stock" alternator that came on the truck in '99.

It IS doable but now I also know the larger refrigerators with a freezer will most likely pull more amperage and my Nissan MAY not could handle it. I'm simply stating my scenario and how it's worked for me over the years.

The "burning propane" argument is a long-time Ford/Chevy debate that's been on this forum for YEARS. Personally, I still prefer my propane tank to be OFF when I'm traveling. And, unless I boon dock- which is once about every 2 yrs- and unless I want to furnish my lil red campfire or a grill, I dont even CARRY my propane tank!
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Old 08-06-2020, 10:11 AM   #9
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It depends on your trailer and tow vehicle. I have an Escape 19 with 150 watts of solar on the roof. My tow vehicle is a Jeep Grand Cherokee with towing package. I always run the refrigerator on 12 v when traveling. I always arrive with the trailer batteries, 2 6 volts, at least as well charged as they were when I started traveling, and the refrigerator cool, usually about 36 degrees. And this often includes a stop for lunch when I leave the trailer and tow vehicle connected.
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Old 08-06-2020, 10:12 AM   #10
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I tow with the Dometic fridge on the 12VDC setting. My Toyota Tacoma, with the towing package, has an appropriate alternator that seems to be more than capable to provide power to the trailer via the 7 pin connector. Also, it has a solenoid cutoff to prevent battery drains while parked. After hooking up to 120 VAC, I change to the AC setting (or LP if needed) I hope I don't jinx it, but The whole system seems to perform well (so far).
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Old 08-06-2020, 10:24 AM   #11
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We've been doing it for years. TV is a Hyundai Sante Fe Sport Turbo. Freeze a few plastic bottles with drinking water to help keep the fridge cool while traveling. The heat of the open road is hard on a fridge! For best results, cool your fridge on shore power a day or two prior to leaving home.

Don't leave the TV attached for more than a 30 minute lunch break or you'll start to draw down the TV battery. When your frozen water bottles thaw, you have fresh water for drinking or making coffee.

We always find the fridge temps in good range when arriving at the campground.
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Old 08-06-2020, 10:27 AM   #12
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Charging the RV battery with your TV is little more than a trickle charge and will not handle the frig. I tried for the first time running the frig on 12V while charging with a 100W solar panel. While it was able to keep up with the demand, the frig did not cool well. I couldn't get it to cool much more than about 15C where 4C is recommended.
I find these frigs run best on 120V, second best on propane and that neither is very good.
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Old 08-06-2020, 01:34 PM   #13
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Ditto. Me too! Sometimes I'll pre freeze a 'freezer pack' at home and stuff it in the Dometic while I'm travelling. Running propane while underway never seemed like a good idea to me!
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Old 08-06-2020, 01:40 PM   #14
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Re: running refrigerator on road - Transport Canada response
Hi Glenn:

Your question was forwarded to the Inspector Education and Public Awareness Division of the Transportation of Dangerous Goods (TDG) Directorate within Transport Canada for response.

The answer is yes, under the Federal Transportation of Dangerous Goods (TDG) Regulations the refrigeration system may be used while the RV trailer is in transit. However, we suggest that you contact the province in which you intend to operate your vehicle to verify if they have any additional requirements. For instance, you may not be able to operate your system in a tunnel or you may be limited to two cylinders. Also, you may face other limitations when you’re on a ferry. Finally, we suggest that you verify with your trailer manufacturer to verify their position on this subject.
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Old 08-06-2020, 03:10 PM   #15
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This same discussion comes up every time someone new buys a trailer. Absorption fridges are not as efficient as compressor types but they do work well if properly installed. Since they use a heat source to operate, they must dissipate the operational heat as well as the heat from inside.

Some will operate on propane while driving but some won't. Propane operation is unsafe while refueling and not permitted in some locations.

12V operation while traveling uses more power than most wiring provides. If your trailer battery falls below 12.5V with the fridge on and the tow vehicle running, you will drain your trailer battery while driving.

Work arounds have been suggested on this thread and many others. My solution is to run 110 to the fridge from an inverter in the car. Many other solutions are just as good.
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Old 08-06-2020, 05:42 PM   #16
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Originally Posted by Lynn Eberhardt View Post
My solution is to run 110 to the fridge from an inverter in the car. Many other solutions are just as good.
That's a very clever approach. By raising the voltage, you have overcome the whole voltage-loss issue very nicely.

When I was in school, we calculated the diameter of an imaginary 240-volt copper transmission line to serve a small town and it was some ridiculous number like two-meters in diameter.

On the other hand, now we will probably have posts about the risks of running 120 volts through an extension cord from the vehicle to the trailer, stuff like that.

And Glenn will have to write a whole new letter to the authorities to get additional clarity on the issue.
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Old 08-06-2020, 06:12 PM   #17
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Originally Posted by Evirk View Post
I have looked at past posts regarding this issue in the forum. There is some disagreement regarding running the Dometic fridge on 12 volt while towing. The issue comes down to whether or not the tow vehicle alternator can keep up with the load of the fridge as well as the normal load of the tow vehicle electrical system. There are also remarks that indicate that it might work if only the towing harness is wired with #10 wire (nobody does that).
No doubt this will vary by tow vehicle. In our case we have a 2007 Dodge Dakota pulling a Casita 17 Spirit Deluxe. It seems to me that if I put the fridge on 12 volt, check the battery voltage, then start the fridge and again look at the battery voltage while the tow vehicle is hooked up and running I should be able to confirm if the battery is charging or draining by looking at the battery voltage using the monitor we bought that plugs into the 12 Volt receptacle. However, Iím not sure what voltage to look for.

It seems to me that any voltage above 12.65 volts for a fully charged lead acid battery should indicate Iím ahead of the game instead of falling behind. Has anyone else looked at this?

We are traveling to PA from VA in a week and a half and I donít want to be sitting beside the road with a dead tow vehicle battery because the fridge pulled it down. On the other hand, what good is 12V if you canít run the fridge while towing? Boondocking I can see how it would drag the house battery down in a matter of hours. Then it would be propane or nothing. But towing? Like I said, if I canít run it while towing, whatís it even good for?
We towed our 17' Casita with our GMC Yukon XL and once accidentally bumped the button for 12V. By noon our Casita battery was almost dead eventhough the output on the Yukon was real good at almost 14V. The fridge was getting warm also. I would not tow with the fridge on 12V. Been there done that and never again. Fortunately we found it before we lost our food. Fridge keeps food cold but once off or not enough power it doesn't stay cold. We keep a thermometer in it and read it remotely so we don't have to guess if it is cold enough. The 12V really isn't worth much on these fridges. We only use it from the campground to the gas station if getting it close by so we don't have to stop and shut down the fridge before pulling up to the pump. Then we pull away and put it on propane. Don't pull up to the pump with the fridge on propane as the flame could ignite any fumes from the gasoline from any bodies pump not just yours. Also never put it on propane while you are by the pumps.
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Old 08-06-2020, 06:12 PM   #18
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Solar to charge battery to run refrigerator

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Originally Posted by hwdornbush View Post
...I have an Escape 19 with 150 watts of solar on the roof......I always run the refrigerator on 12 v when traveling. I always arrive with the trailer batteries, 2 6 volts, at least as well charged as they were when I started traveling, and the refrigerator cool, usually about 36 degrees.....
Yes, consider getting solar to keep the trailer battery charged to run the refrigerator.
We have 100 watt solar panel that keeps the battery charged that keeps the refrigerator running while traveling and Boondocking.
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Old 08-06-2020, 11:13 PM   #19
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Or, you could just run the fridge on Propane while going down the road like 99.99% of campers do. There is almost no reason to try to run the fridge on 12 volts. Even with dual alternators and dual batteries on our truck and 320 watts of solar on the roof, I don't even bother with it.
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Old 08-07-2020, 07:50 AM   #20
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"It seems to me that any voltage above 12.65 volts for a fully charged lead acid battery should indicate I’m ahead of the game instead of falling behind. Has anyone else looked at this?"
Yes. I always use our fridge on 12VDC while towing with no battery or cooling issues. I do switch to 120VAC at the campground. Our Parkliner does have two 12V batteries and I monitor them the same way as you. Our Grand Cherokee has factory installed tow package and automatically cuts off TV battery/charging power to the camper if the engine is off. This was one reason I wanted factory installed towing.
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