Inverter for running fridge while traveling

[Larry-NC]

Originally Posted by JLeising

With regard to refrigerator damage from running out-of-level, don't think it matters if the fridge is run on propane or on electric...

Actually it does matter. A dual-mode refrigerator contains two separate systems:

• A fluorocarbon (e.g., Freon) system when running on shore power
• An ammonia+water system when running off propane

The failure only occurs when the ammonia is circulating. This

video

shows schematically how the ammonia system works.

As I get it, the problem occurs at the evaporator (lower left) where the ammonia drips into the "fountain". In the real structure (not the cartoon video), if it drips off to the side instead of in the middle, damage occurs. Another individual said the refrigerator needs to be level within 3 degrees (one-half bubble). Since most refrigerators (including ours) are on the sidewall of the trailer, that means the trailer needs to be nearly level front-to-back. That in turn means don't run it if parked on a hill.

Larry

[Magsomal]

Originally Posted by bikendan

What's this have to do with running a fridge on the road?[emoji848]

Ha.. I don’t know what it has to do with the refer..BUT that is my backyard & my pop up and my very dear friend Matteo Giovanetti doing the install video on the Micro Air smart start[emoji3][emoji1376][emoji1376] IT WAS A FUN DAY[emoji3]

[IndianKen]

I carry my motorcycle in my toy hauler and prefer not to run the fridge on propane during travel which means we do not run the fridge at all. We pre-cool the fridge on shore power and fill the bottom tray with ice and another smaller tray filled with ice in the freezer. it has worked pretty well for several days at a time and get more ice along the way (if needed).

[JLeising]

Originally Posted by Larry-NC

Actually it does matter. A dual-mode refrigerator contains two separate systems:[LIST][*]A fluorocarbon (e.g., Freon) system when running on shore power[*]An ammonia+water system when running off propane

On mine (Dometic 2652 I think) only one cooling system- the ammonia system. On electric, mine uses a 120 volt heater to boil the ammonia mixture. On propane it uses a small propane flame.
I think most RV refrigerators are like mine. Some are three way - still only use one ammonia based cooling loop, but add the option of a 12 volt heater to boil the ammonia mixture.
I not aware of a dual system like you mentioned. It sounds interesting, though.
I have seen 12 volt compressor/freon refrigerators ("trucker's refrigerators"). They use a very efficient compressor and freon system - but don't run on propane. There is a tendency today to put standard home compressor and freon refrigerators in high end rv's, with very large battery packs and inverters - again, no propane option.

[rockfordroo]

Originally Posted by JLeising

On mine (Dometic 2652 I think) only one cooling system- the ammonia system. On electric, mine uses a 120 volt heater to boil the ammonia mixture. On propane it uses a small propane flame.
I think most RV refrigerators are like mine. Some are three way - still only use one ammonia based cooling loop, but add the option of a 12 volt heater to boil the ammonia mixture.
I not aware of a dual system like you mentioned. It sounds interesting, though.
I have seen 12 volt compressor/freon refrigerators ("trucker's refrigerators"). They use a very efficient compressor and freon system - but don't run on propane. There is a tendency today to put standard home compressor and freon refrigerators in high end rv's, with very large battery packs and inverters - again, no propane option.

X2

[Larry-NC]

Originally Posted by rockfordroo

X2

I stand corrected.

[Jim D]

I installed an inverter for that purpose and it works great. It's connected to my house batteries which are charged by the engine's alternator when we're on the road. That's the only time I use it so I'm not drawing the batteries down. A 2000W inverter will have no problem running your 'fridge.

[IndianKen]

How much current does the inverter draw?

[Jim D]

I think I'm drawing about 30 amps on the DC side, which is about what others are saying. The 'fridge is rated 2.7 amps @ 120v AC. I'm using a 700w (1400w peak surge) inverter. Keep in mind, I wouldn't do this if my engine alternator wasn't connected to the house batteries. I only use it when the engine is running (except for short stops), even though I have 2 deep-cycle batteries. The inverter is hard-wired to the batteries, and has a low-voltage warning and shut-off, just in case. I already had the inverter and I wasn't using it, and it was relatively easy to set up, so I thought why use propane when I'm on the road if I don't have to?

[rockfordroo]

Originally Posted by Jim D

I installed an inverter for that purpose and it works great. It's connected to my house batteries which are charged by the engine's alternator when we're on the road. That's the only time I use it so I'm not drawing the batteries down. A 2000W inverter will have no problem running your 'fridge.

Some comments for people who may not be up to speed on these issues:

1. Since Jim D used the term "house batteries" I am concluding that he has a motorhome (Class A or C). Motor home house batteries are much better set up for charging from the engine than trailer batteries (large wiring; short wiring runs). Trailer batteries are charged from the tow vehicle via the 7-pin umbilical cord. This is usually via a 12-14 gauge wire and it could be 20 ft long, creating a large voltage drop, so you don't get much current flow.

2. When figuring currents, 12VDC is 1/10th of 120VAC, so DC current into the inverter will be about 10 times greater than AC current out of the inverter. Since watts = volts x amps, then amps = watts/volts. So a 325 watt fridge heater will draw 325/120 = 2.7 amps AC. Therefore, the inverter will need to supply 2.7 amps at 120VAC to the fridge, and it will draw 2.7 x 10 = 27 amps DC from the battery. Given that nothing is 100% efficient, it will probably draw more like 28 or 29 amps from the battery.

3. Putting #1 and #2 above together, you can see that for trailers, you almost certainly won't be able to supply 27-29 amps from the tow vehicle, therefore you will be discharging your trailer battery going down the road. (Jim D's 2000 watts inverter, if supplying the full 2000 watts, will be drawing 160 amps from his motorhome; that requires LARGE battery cables and short wiring runs, not to mention a large alternator.)

4. If you have a 100 amp-hr battery (which you shouldn't deplete below 50%) you'll safely get 50 amp-hr from it, or a little less than 2 hours of powering the fridge. Get a 200 amp-hr battery and you can go maybe 4 hrs. If the fridge is already cold when you start and just needs to cycle on/off, you may get a few more hours out of it. So to start, as discussed above, you should definitely start by installing a 2nd battery. Two 200 amp-hr batteries would give you a total of 400 amp-hrs, or 200 useful amp-hrs. Then, the question of how long you can support powering the fridge will depend on a number of things: How big are the batteries you've installed, how hot is it outside (i.e., how often must the fridge cycle to keep it cold), exactly how much current is your specific tow vehicle supplying to the trailer batteries, exactly how efficient is the inverter you've chosen.

[dronning]

Originally Posted by JLeising

Driving the motorhome (with the vehicle alternator to maintain the house batteries) for, say, 10 hour days in the desert (high ambient temp) - if unwilling to drive with the propane on for safety reasons - might rationalize the mod.

FYI, Jim

The reason I wanted to pursue this is I usually drive straight through and 18-24 hour trips with just gas stops and short bio/food breaks are very common for me.

I have done the math I'm running a 300amp alternator with 2 tow vehicle deep cycle batteries plus the RV battery. The charging circuit to the camper is 30amps so I should be able to stay ahead of the fridge requirements.

BUT since many have suggested just running the propane and it seems fairly common that's the route I will take.

Thanks for the feedback, learning more every day.
- Dave