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Old 06-01-2014, 09:04 AM   #1
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Making a 2-way Fridge into a 3-way Fridge?

In theory, one could add a 12v, 275 Watt heating element to a 2-way fridge to make it a 3-way fridge. Any thoughts? I haven't looked at the "boiler" where the element goes as mine was recently replaced by the previous owner. Could an element be added in there somewhere and be effective? Clearly, only one heat source would be used at a time.

The idea being that, while moving down the road, 12V from the TV would supply the energy for the fridge thus eliminating the concerns about keeping propane on and burning safely. 12V 275 Watt may not be as effective as propane, but in the right conditions, it should work to at least keep the boiler somewhat hot and the fridge somewhat cold.
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Old 06-01-2014, 09:30 AM   #2
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In theory, one could add a 12v, 275 Watt heating element to a 2-way fridge to make it a 3-way fridge. Any thoughts? I haven't looked at the "boiler" where the element goes as mine was recently replaced by the previous owner. Could an element be added in there somewhere and be effective? Clearly, only one heat source would be used at a time.

The idea being that, while moving down the road, 12V from the TV would supply the energy for the fridge thus eliminating the concerns about keeping propane on and burning safely. 12V 275 Watt may not be as effective as propane, but in the right conditions, it should work to at least keep the boiler somewhat hot and the fridge somewhat cold.
You should be aware of the 12 volt current drain.

W = E x I

I = W over E

That spells out you current drain, which will be 23 amps.

It's not worth it to make that conversion.

Andy
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Old 06-01-2014, 10:34 AM   #3
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Andy's right - 23 amps is a heck of a lot of power, especially considering that you're trying to get that current from the tow vehicle alternator, though the vehicle wiring harness, through the tow connector, then through the trailer fuse box and wiring and over to the fridge. In my ever-so-humble opinion, you'd want to use 4 AWG wire, or take a chance on something getting way too hot.
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Old 06-01-2014, 12:37 PM   #4
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12VDC conversions are possible as most cooling units already have a second steel sleeve to hold the DC heating element. You would have to install larger DC wiring for this element and a new control board. Still, the 12VDC option is only for maintaining the fridge temp and will not cool down a warm fridge.

A better option might be a marine fridge that uses a Danfoss compressor. AC or DC use and very efficient with Los amp draw.
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Old 06-01-2014, 12:51 PM   #5
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The idea being that, while moving down the road, 12V from the TV would supply the energy for the fridge thus eliminating the concerns about keeping propane on and burning safely.
Just run the propane. Propane fires/explosions are vanishingly rare in RVs. Most fires are electrical in origin. By the numbers you'd be better off for safety by turning off the 12v at the battery disconnect and leaving the propane on.
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Old 06-01-2014, 01:01 PM   #6
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Eight or ten gauge would suffice for 25 amps @ 25 feet.

A simple switch rated at 25 amps would do in a pinch. What the computer don't know.....

http://www.offroaders.com/tech/12-vo...gauge-amps.htm
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Old 06-01-2014, 01:29 PM   #7
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The real watts from the Dometic web site is 150 on the 12VDC and 12.5 amps. That's on the RM2353 and the 120VAC watts is 175 for 1.5amps.
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Old 06-01-2014, 01:38 PM   #8
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Fwiw, I agree with using the propane.
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Old 06-01-2014, 04:04 PM   #9
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There is a reason for 3-way fridges otherwise they wouldn't make or sell them. That being stated, I was hoping to get to the practicality of adding 12V for whatever reason one had to do so. The risk of running propane was just one example. Perhaps the 12V element could be smaller in wattage? I believe there are also combination elements out there.
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Old 06-01-2014, 04:07 PM   #10
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I think the idea will work so long as the fridge has a spot to install the element.
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Old 06-01-2014, 05:44 PM   #11
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Originally Posted by Bunkroom View Post
There is a reason for 3-way fridges otherwise they wouldn't make or sell them. That being stated, I was hoping to get to the practicality of adding 12V for whatever reason one had to do so. The risk of running propane was just one example. Perhaps the 12V element could be smaller in wattage? I believe there are also combination elements out there.
The 3 way is much more practical in a motorhome as you are much closer to the batteries and alternator.
Even at that it is a big load and only maintains the temp.

Just run with the propane on
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Old 06-03-2014, 09:01 AM   #12
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There is a reason for 3-way fridges otherwise they wouldn't make or sell them.
For a time from the 1970s to the 1990s, small 3-way fridges were popular in motorhomes and, to a lesser extent, truck campers and pop-ups. That is because, during that era, RV fridges did not have electric ignition. It was common for the propane flame to blow out while running down the highway, so 12v operation was more reliable.

A secondary reason they were used was that small motorhomes tended to have limited propane capacity, and their owners found it more difficult logistically to fill propane than do trailer owners since it motorhome tanks are typically not removable (there are exceptions).

3-way fridges have never been widely used in travel trailers (except pop-ups) because it is rare for the charge line from the vehicle to provide sufficient power for them to work well.

Quote:
That being stated, I was hoping to get to the practicality of adding 12V for whatever reason one had to do so. The risk of running propane was just one example. Perhaps the 12V element could be smaller in wattage? I believe there are also combination elements out there.
It's a hassle and I'll bet you'll never actually build it and use it. You have to add the element and then figure out a way to control it. If you have the 2-way model of a fridge that is also sold as a 3-way then maybe you can add the element and the relay and replace the control board. The larger fridges aren't made in 3-way models so you'll have to make up some of that from whole cloth.

A few months ago someone wanted to run the 120v side of their 2-way fridge off an inverter citing the same "I don't like gas, gas explodes" line of reasoning. They never built it either.
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Old 06-03-2014, 09:59 AM   #13
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Damn, must most every thread be a war of wills?

I would run propane going down the road, but that isn't what the op asked.

He asked whether it is possible. I say that if the fridge has provisions for a 12 volt element it should be possible.

And since it is pretty much consensus that a 12 volt element is marginally sized, meant for maintenance, I don't see why its "control " couldn't simply be a toggle switch.

The refrigerator control would never even need to know that the 12 volt element is even present.
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Old 06-03-2014, 10:03 AM   #14
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Making a 2-way Fridge into a 3-way Fridge?

By the way, there is a 7.1 cuft Norcold on eBay, so apparently three ways are not exclusive to tiny trailers with tiny refrigerators.

Most tow vehicles have alternators that produce well over 100 amps. On GM vehicles the trailer hot line is fused at 30 or 40 amps.

In my Sovereign I run a 10cu ft residential fridge on an inverter, my tow vehicle keeps up with and gains on the draw going down the road.

There is more than one way to approach an issue.
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