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Old 01-21-2010, 10:31 PM   #1
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1974 31' Sovereign
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Anyone have a refer that goes three ways?

Since we have begun to travel now, we plan on replacing the AC-only fridge in our trailer this year, and I've seen the comments in several threads that say it isn't safe to tow with the LP running the refer.

Therefore, I am thinking that it might be A Good Thing to have a 3-way refer: LP/120VAC/12DC since in this way we could always have Cool Food on hand.

Looked at Dometic's site, and there do not appear to be a lot of models like that.

Am I missing some negative point to having a 3-way? It looks like all the new ones require a 12V supply nEwayz, to run the Fancy Stuff they offer, so what are the potential drawbacks?

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Old 01-21-2010, 11:48 PM   #2
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Well, I'm no expert, but I believe a refer running on 12v would drain the batteries very quickly! Likely to the point that the manufacturers don't see the need for the extra expense to make them when they wouldn't be much in demand. I had a camper (hardtop trailer) that had a 3 way, and if we ran it on 12v while teravelling and forgot to unplug while stopped for any length of time, it would drain the car battery! Consequently, we never ran it on 12v. The 12v connection in most 2 way refers that I have been exposed to is just to open the valve and fire the igniter while set to auto for gas operation if the 120v fails.

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Old 01-22-2010, 05:35 AM   #3
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I'm not sure why some people say it is not safe to have your propane running on your furnace while traveling. I have never seen anyone say exactly why or anyone who had a propane problem or fire as a result. The burner flame little bigger than a pilot light and is well shielded. The whole area is vented both through the floor and roof. I do it all the time.

But your fridge will stay cold or at least cool for some time when turned off.
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Old 01-22-2010, 06:22 AM   #4
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Most RV fires involve the propane system at some point. While it's difficult to catch your trailer on fire with the fridge, it is possible. The larger threat, however, is if you crash and rupture a line and allow 60-80 lbs of propane to vent into the crash site. The tanks and valves themselves are pretty tough though.

I have had both three-way and two-way fridges. The 12v option is only for running down the road when the alternator is feeding the 12v power. Honestly, if you just keep your fridge closed during your travels, your food will stay just fine. Few of us travel more than 12 hours at a stretch, and generally a cold fridge will stay cold that long... and certainly for any length of time less than that.

Fridges are expensive gizmos... if your two-way works, then just leave it and use it. Cool it down before you go, unplug or turn the gas off and go. Turn it back on when you get to your destination. You'll be fine. In the event you're traveling a LONG ways, just freeze some ice packs ahead of time, and leave them in the fridge with the food too.

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Old 01-22-2010, 07:10 AM   #5
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A lot of controversy on running things on LP when running down the road. I currently have a 3 way fridge, we cool it down at home before a trip then add ice packs from our deep freeze right before we leave. It stays shut off until we get where we are going. I have run the 12 volt on the smaller fridge in my popup because it was very small and hard to keep cold due to the smaller mass.

I am more prone to run my furnace while running down the road especially in very cold weather.

The OPD valves on the cylinders are supposed to stop a sudden flow of gas in the case of a line rupture. My biggest concern with open flame ie; pilot lights and furnace flames is when refueling. If I know I am going to have to refuel I will stop short of the pumps or even the entire gas station and turn the furnace OFF prior to pulling up to the pumps.

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Old 01-22-2010, 07:11 AM   #6
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Good question.

There are two trends to be aware of in the RV fridge world, that are leading to the decline of the traditional 3-way fridge:

1) There is a trend towards larger fridges. Because of the higher current requirement, these are set up as 2 way (120v/LP) rather than 3 way. The larger 2 way fridges have 325 watt elements which means they would draw around 25 amps at 12 volts if they were set up as 3 way, which is not thought to be practicable in most cases.

In theory the larger volume leads to an improved ratio of thermal mass to heat loss, so these fridges don't warm up much while under way even if the cooling unit is off.

2) With the introduction of the brushless 12 volt compressor from Danfoss a few years ago, there are smaller fridges available that are 12 volt only (no LP) with extremely low current draws compared to the old 3-way models, typically around 3 or 4 amps. They work the same way as home fridges, with a fluorocarbon refrigerant and a compressor, and are much more efficient than the ammonia absorption systems used in LP fridges. These also do not have the demanding venting requirements of LP fridges and are somewhat cheaper. Typically they are no larger than 3-4 cubic feet.

With these the idea is that they run off the converter when plugged in, and the power consumption is low enough that they can run off the battery overnight if necessary.

Sportsmobile, one of the more prominent van conversion companies, has pretty much switched over to these, though they still offer a 3-way as an extra-cost option for people who really want them.

There are endless debates on the safety of operating propane appliances while under way. I have seen a lot of hand wringing and theorizing but no actual evidence of this sort of thing having contributed to injury or property damage in a real-life crash. Many people run propane fridges while under way without incident.
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Old 01-22-2010, 07:18 AM   #7
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Aage, the fridge in our '63 was a 3 way fridge, and I left the 12 volt cooling part disconnected when I installed it. I have seen many more circuit board failures from using 12 volts than I have when only 120v/LP was used. There are real issues with voltage fluctuation, even when plugged into the TV and towing. The voltage will drop when you stop at a traffic signal, and go up again when you take off.
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Old 01-22-2010, 08:15 AM   #8
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When we replaced our refrigeraor, we replaced with a Dometic RM 7401, which is a European model not often available in the US. It is three way, but the instructions were quite specific: The 12V lead was to come directly from the tow vehicle, not powered through the on-board 12V system.

Yes, I know. In the end, we decided just not to hook up the 12V part. We've never had a problem with defrost while underway, so no particular reason to have to use the 12V system for it.

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Old 01-22-2010, 10:38 AM   #9
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We have a newer but not brand new Dometic RM2607 3 way fridge in our TradeWind. I can tell you that it will fry a battery in about three hours if only powered with 12 volts. I had the trailer plugged in at my old house to shore power and when my daughter went out to swim, she unplugged the trailer to plug in her music. I found out that evening and the fridge had self-switched over to 12 volt after the 120 volt supply was stopped.

Approximately nine months ago, I also put in a new Dino circuit board and the fridge now works great, even below 12 volts. Easy switch out.

We don't travel with the fridge on but freeze a gallon of drinking water the night before departure and put it in the fridge before we leave. While we're out, the drinking water gets put to use so we're not wasting any precious fridge or freezer space with cooler packs.

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Old 01-22-2010, 12:53 PM   #10
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What everyone else said

Pack your freezer solid with frozen food or add a bag of ice if you don't want/need that much in your freezer. A Frozen gallon or half gallon bottle of water in the main compartment is a good add on too. I live in Virginia and travel this way all the time... even in summer I've never had a thaw out.

Another alternative - do you always have to pack your food before you travel? The world is full of grocery stores and most have big parking lots. If you want to carry a local specialty fine, but eggs, milk, hamburger, etc.? Get them at or near your destination.

I find it very difficult and fatiguing to tow 8-10 hours straight, and often stop for lunch and an half hour nap - I will turn on the propane during that interval.

If I were planning on a long drive followed by boondocking, I might get some dry ice and fall back on the old coleman cooler kept in the air conditioned tow vehicle for the expensive or easily spoiled stuff - especially mayonaisse or anything else that likes to breed botulism.

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Old 01-22-2010, 05:24 PM   #11
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We have a new 3-way Dometic. We bought it because we wanted to be able to use our solar power system on occasion, or if needed. We have ended up using almost exclusively LP Gas as it is the most efficient. We occasionally use 120V if we are hooked up. The 12V is purely a back up at this point and I think it is overkill unless you tend to run out of gas from time to time! As far as running while driving, we have put on 20,000 miles with the fridge running on LP while driving. Tanks are designed to shut of immediately in case of a line rupture of any sort. Not worried about it at all. I'd probably go with the 2-way.
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Old 01-22-2010, 05:29 PM   #12
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OK, thanks to you all for your input. It seems clear now why the models feauring 12VDC capability are few in number.

This makes for a wider choice and lower price, as well as a simpler installation to just go with a two-way refer.

And thanks too for all the tips on how to stretch out the chill in the refer. I've made notes of them and will try them all out.

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Old 01-22-2010, 07:26 PM   #13
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We have a large power boat that we have traveled extensively throughout the Great Lakes, Rivers and the Eastern part of the United States. It has a Dometic refridgerator that is the same size as the one in our A/S. It runs on 120V when available and automatically switches to 12V Direct current when no 120V AC is available. It is really a 120V refridgerator with a built in Inverter that converts 12V to 120V when needed. We have two breakers in the power panel for the refridge. One is in the AC panel and one is in the DC panel. I have thought about hooking a small inverter to our A/S fridge and accomplishing the same thing. The only problem is the battery bank on our boat is huge compared to the trailer. On the boat we can run the fridge for 24 hours without AC power. As long as the tow vehicle is hooked up and running you should have plenty of power but if you park without turning the fridge off or on to LP gasit would run the battery down pretty quickly.
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Old 01-22-2010, 08:33 PM   #14
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Originally Posted by Aage View Post
And thanks too for all the tips on how to stretch out the chill in the refer. I've made notes of them and will try them all out.

Tossing a bag of ice into the freezer compartment will do two things. One, it will help keep things cold, and two, you will have ice cubes for your drinks when you get where you're going.

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