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Old 09-16-2015, 10:31 AM   #1
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Using inverter for Fridge at high Altitude

Not exactly sure where to post this topic. We usually dry camp and from sea level to 10,000 feet. Had little problems with our Norcold N611 in our Winnebago. Wondering what surprises our new Forester with the Dometic will hold. In reading other topics, some have encountered issues with pilot not lighting at higher altitudes because of lack of oxygen. Has anyone every tried using an inverter rigged between the battery bank to the 110v wire for the fridge? If so, how many amps does the fridge draw and what size inverter would be needed? My batteries are 2 group 27s and I can easily recharge it with the generator during genny hours or use my Renogy 130 watt solar. This setup would only be used for 2-3 days at most.
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Old 09-16-2015, 11:07 AM   #2
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Mine uses about 5-6 amps on electric. An inverter of 1000watt output constant would be a good choice to run the frig and TV on 120v. If you figure using about 130-150 amps in 24 hours for all sources, you will only last 1-1.5 days with two batteries before needing to recharge. Best not to let batteries go below 50% charge before recharging.
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Old 09-16-2015, 11:22 AM   #3
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Big Vic, the fridge will already be cold and running for days, so it won't be running continuously, but cycling. I figure about 100 amps per day then and running the generator for a few hours plus the solar should give me about 3 days then.
I am going to unplug the fridge and use my Kilawatt to see what the 110v amps are. I have a 400 watt inverter and perhaps if that works I can get the amp draw with my meter to see exactly what the 12v amp draw is. May need to buy a bigger inverter then. Wonder if that Harbor Freight one would do the trick. Nothing else would be on the circuit.
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Old 09-16-2015, 01:05 PM   #4
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Checked 110v amps and watts, 2.7 amps and 324 watts. So an 800 or 1000 watt inverter should do the job. Can always buy 2more batteries also.
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Old 09-17-2015, 02:54 PM   #5
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Not exactly sure where to post this topic. We usually dry camp and from sea level to 10,000 feet. Had little problems with our Norcold N611 in our Winnebago. Wondering what surprises our new Forester with the Dometic will hold. In reading other topics, some have encountered issues with pilot not lighting at higher altitudes because of lack of oxygen. Has anyone every tried using an inverter rigged between the battery bank to the 110v wire for the fridge? If so, how many amps does the fridge draw and what size inverter would be needed? My batteries are 2 group 27s and I can easily recharge it with the generator during genny hours or use my Renogy 130 watt solar. This setup would only be used for 2-3 days at most.
That might be a backup plan, but when I accidentally ran my refrigerator on the inverter I suddenly realized it was pulling about 400 watts and with our big 2000 watt pure sine wave inverter, I think that translates to about 40 amps 12 volt. My solar charging system is good for about six and a half apps or so per hour on an average day so I'm thinking that might not be so good by the end of the day. Unlike a residential refrigerator that only draws with the motors running, the heating element in an ammonia base refrigerator seems to run continuously. Seems like maybe you would need more batteries and more solar to run continuously on 120 volt.
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Old 09-17-2015, 02:57 PM   #6
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Mine uses about 5-6 amps on electric. An inverter of 1000watt output constant would be a good choice to run the frig and TV on 120v. If you figure using about 130-150 amps in 24 hours for all sources, you will only last 1-1.5 days with two batteries before needing to recharge. Best not to let batteries go below 50% charge before recharging.
That sounds about right, but I think overlooks the fact that a four amp draw @ 120 volt is more like a 40 amp draw at 12 volts, where in there may be a problem. The modified sine wave inverters are little more efficient than the pure sine wave and should be okay for a heating element where as not so good for sensitive electronics or electric motors. But still I think calculating the draw will suggest the need for more batteries. And maybe more solar.
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Old 09-17-2015, 03:09 PM   #7
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[QUOTE=Sagecoachdriver;985424]Checked 110v amps and watts, 2.7 amps and 324 watts. So an 800 or 1000 watt inverter should do the job. Can always buy 2more batteries also.[/QUOT

So here it is on these numbers. 324 watts will pull about 32 amps 12v so times 24 hours divided by 105 reserve amps or about 7 group 27 batteries dead in 24 hours.

May be I am wrong and the refrigerator does not draw continuously when on 120v. I caught mine after an hour of running steadily at almost 400 watts and never repeated it for testing purposes. Anyway, I understand they don't build too many refrigerators to run volt, maybe for that reason, it would only be feasible of the automotive alternator or the generator is running. Good luck

I bet you could run it through the kilowatt meter for 24 hours and register the cumulative usage, just as a test while you are still at home
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Old 09-18-2015, 11:32 AM   #8
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I installed an 1K modified sine wave inverter in my 2011 Georgetown 327DS when I purchased it. The inverter was wired to provide power only to the Dometic fridge and the original AC power line for the fridge was rerouted to the inverter as its shore power feed. The inverter has its own internal transfer switch so it self disconnects whenever AC power is available from the generator or a campground's power outlet. The inverter's control panel is mounted remote from the inverter, just below the sink where it's easy to see and use.

When running on AC, the Dometic fridge draws around 300W. The fridge does cycle the AC power draw, using it only when needed to keep the fridge cold, the same way it does when running it on propane. The 300W draw pulls around 24A from the battery. Two deep cycle 100AH batteries will provide 100A of power (drawing them down to 50% of capacity) which is around 4 hours of cooling for the fridge. I figure that worst case, the fridge will be actively cooling 50% of the time which means that I can run the fridge for 8 hours on batteries before venturing into the "how low can you go without damaging the battery" zone. Don't forget that discharged batteries need to be recharged to prevent sulfation of the plates. If you're running the fridge on batteries, how will you recharge them?

Your batteries also power your interior lights, propane detector, furnace fan, water heater controls, and a host of other small things you didn't know were connected to the battery. Running the fridge on batteries sounds like a good idea but, in the long run, doesn't appear to be a good choice for dry camping unless you have at least 500W of solar power available or are planning on running the generator for at least 4-5 hours a day.

I use my inverter to power the fridge only when driving or making a short stop, usually less than one hour. With the motor running, I have a 175A alternator providing power to chassis and house batteries so the 24A draw for the inverter isn't an issue. This allows me to drive with the propane shut off, a good thing to do from a safety standpoint.

Phil
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Old 09-18-2015, 11:58 PM   #9
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Originally Posted by pmsherman View Post
I installed an 1K modified sine wave inverter in my 2011 Georgetown 327DS when I purchased it. The inverter was wired to provide power only to the Dometic fridge and the original AC power line for the fridge was rerouted to the inverter as its shore power feed. The inverter has its own internal transfer switch so it self disconnects whenever AC power is available from the generator or a campground's power outlet. The inverter's control panel is mounted remote from the inverter, just below the sink where it's easy to see and use.

When running on AC, the Dometic fridge draws around 300W. The fridge does cycle the AC power draw, using it only when needed to keep the fridge cold, the same way it does when running it on propane. The 300W draw pulls around 24A from the battery. Two deep cycle 100AH batteries will provide 100A of power (drawing them down to 50% of capacity) which is around 4 hours of cooling for the fridge. I figure that worst case, the fridge will be actively cooling 50% of the time which means that I can run the fridge for 8 hours on batteries before venturing into the "how low can you go without damaging the battery" zone. Don't forget that discharged batteries need to be recharged to prevent sulfation of the plates. If you're running the fridge on batteries, how will you recharge them?

Your batteries also power your interior lights, propane detector, furnace fan, water heater controls, and a host of other small things you didn't know were connected to the battery. Running the fridge on batteries sounds like a good idea but, in the long run, doesn't appear to be a good choice for dry camping unless you have at least 500W of solar power available or are planning on running the generator for at least 4-5 hours a day.

I use my inverter to power the fridge only when driving or making a short stop, usually less than one hour. With the motor running, I have a 175A alternator providing power to chassis and house batteries so the 24A draw for the inverter isn't an issue. This allows me to drive with the propane shut off, a good thing to do from a safety standpoint.

Phil
I really like your analysis and can find absolutely no fault with it. So, that leaves only -- can you tell me the model of the inverter and or auto switch you are using. Also, the modified sine wave is considerably more efficient than Pure Sine which is probably not needed in this application.

I absolutely loved you description. Unlike many of mine, I UNDERSTOOD YOURS.

Tom
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Old 10-16-2015, 03:50 PM   #10
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I really like your analysis and can find absolutely no fault with it. So, that leaves only -- can you tell me the model of the inverter and or auto switch you are using. Also, the modified sine wave is considerably more efficient than Pure Sine which is probably not needed in this application.

I absolutely loved you description. Unlike many of mine, I UNDERSTOOD YOURS.

Tom
I purchased a Xantrex XM1000. Less than $250 from Amazon.

A year after it was installed, I added, to the inverter, a GFCI protected outlet at the sink and another one below the sink in the plumbing compartment. The sink outlet is for a slow cooker (300W) when driving while the one in the plumbing compartment services the heating strip that keeps everything in there from freezing when we use the RV in the winter. I'm still under the 1kw rating of the inverter.

Don't forget that a device like this needs large cables from the battery. Mine is installed using 2/0 welding cable with a circuit breaker near the battery and a marine disconnect switch installed at the RV inside entrance steps. The remoted control panel uses standard telephone cable routed under the sink.

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Old 10-25-2015, 06:16 PM   #11
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Angry Fridge on inverter

I just got a new Wildcat with large tanks and a 9 cu/ft Dometic 3962 Fridge for dry camping only to read the operating manual for the fridge and found out that you need to use electric above 5500 feet. I panicked because I spend 2 to three weeks at 9,300 ft in Colorado. Dometic tells me that my fridge pulls 3 amps on 120 volt. My battery monitor tells me that with the fridge on my inverter i am pulling 27 to 28 amps on 12 volt. I run two group 27 batteries. I guess I will run my generator and solar both to keep my batteries up. Does anyone know if they make an oxygen mask for a Dometic RM3962? Never had a problem at altitude with my 6 cu/ft fridges at altitude before!!
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Old 10-26-2015, 11:38 PM   #12
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120V*3A = 360W. 12V*28A=336W.

It looks like they rounded the AC current draw up to the nearest amp when rating the fridge. My 6 cu/ft Dometic draws 25-26A at 12V. Don't forget that the fridge doesn't draw this current all the time, only when it's cooling.

The reason the fridge doesn't work on propane at high altitudes is the design of the mixing chamber of burner assembly. If they designed this the same way that's used for gas grills (which burn much more gas than a fridge burner), it would work at high altitudes.

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Old 11-12-2015, 05:55 PM   #13
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I installed an 1K modified sine wave inverter in my 2011 Georgetown 327DS when I purchased it. The inverter was wired to provide power only to the Dometic fridge and the original AC power line for the fridge was rerouted to the inverter as its shore power feed. The inverter has its own internal transfer switch so it self disconnects whenever AC power is available from the generator or a campground's power outlet. The inverter's control panel is mounted remote from the inverter, just below the sink where it's easy to see and use.

When running on AC, the Dometic fridge draws around 300W. The fridge does cycle the AC power draw, using it only when needed to keep the fridge cold, the same way it does when running it on propane. The 300W draw pulls around 24A from the battery. Two deep cycle 100AH batteries will provide 100A of power (drawing them down to 50% of capacity) which is around 4 hours of cooling for the fridge. I figure that worst case, the fridge will be actively cooling 50% of the time which means that I can run the fridge for 8 hours on batteries before venturing into the "how low can you go without damaging the battery" zone. Don't forget that discharged batteries need to be recharged to prevent sulfation of the plates. If you're running the fridge on batteries, how will you recharge them?

Your batteries also power your interior lights, propane detector, furnace fan, water heater controls, and a host of other small things you didn't know were connected to the battery. Running the fridge on batteries sounds like a good idea but, in the long run, doesn't appear to be a good choice for dry camping unless you have at least 500W of solar power available or are planning on running the generator for at least 4-5 hours a day.

I use my inverter to power the fridge only when driving or making a short stop, usually less than one hour. With the motor running, I have a 175A alternator providing power to chassis and house batteries so the 24A draw for the inverter isn't an issue. This allows me to drive with the propane shut off, a good thing to do from a safety standpoint.

Phil
Phil are you running a special wire from your vehicle alternator or do the 5th wheel 7 pin plug have #10 wire to handle nearly 30 amps?
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Old 11-12-2015, 06:19 PM   #14
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A low-tech, old school solution to the OP's situation (using for only 2 or 3 days) is to use ice. Fill containers like 1 gallon milk bottles, 5 quart oil bottles, tupperware, etc. and pre-freeze them at home. If you are using half or less of the room in the fridge, just put them in there. If you need more space, the standard ice chests. Buy more on the road as needed.

Sometimes less is more.
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Old 11-12-2015, 10:57 PM   #15
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Using inverter for Fridge at high Altitude

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A low-tech, old school solution to the OP's situation (using for only 2 or 3 days) is to use ice. Fill containers like 1 gallon milk bottles, 5 quart oil bottles, tupperware, etc. and pre-freeze them at home. If you are using half or less of the room in the fridge, just put them in there. If you need more space, the standard ice chests. Buy more on the road as needed.

Sometimes less is more.

Thank you for that! A good old five pound block of ice in a Coleman ice chest is a lean, mean cooling machine.
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Old 11-13-2015, 09:51 AM   #16
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Phil are you running a special wire from your vehicle alternator or do the 5th wheel 7 pin plug have #10 wire to handle nearly 30 amps?
The Georgetown is a class A and doesn't have a TV. The engine alternator is wired almost directly to the house batteries to keep them charged. The inverter has a voltmeter function on its display panel and, when the inverter is providing power to the fridge and the alternator is running, it shows over 14V being fed to the inverter. This indicates that there's little, if any, voltage drop in the charging line from the alternator.

A 20' length of #10 wire has a resistance of 0.02 ohms. At 30A, this will result in a 0.6V drop in voltage. If your TV's regulator has the alternator outputting 13.6V, you'll have 13V at the far end of the charge wire, enough to be drawing power from the alternator instead of the battery. Don't forget that when the fridge isn't cooling, the very light parasitic load on the trailer's battery will let almost all of the power from the TV recharge the battery.

Phil
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Old 11-18-2015, 02:30 PM   #17
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I just got a new Wildcat with large tanks and a 9 cu/ft Dometic 3962 Fridge for dry camping only to read the operating manual for the fridge and found out that you need to use electric above 5500 feet. I panicked because I spend 2 to three weeks at 9,300 ft in Colorado....Does anyone know if they make an oxygen mask for a Dometic RM3962? Never had a problem at altitude with my 6 cu/ft fridges at altitude before!!
If you do enough checking, it's not only your fridge that claims it won't work at altitude. Your generator manual will have a similar statement (unless it's fuel injected), saying that different carburetor jets are needed for high altitudes.

Reality is that most continuous burners like stoves and fridges and hot water heaters do just fine at altitude. They may not run quite as efficiently (not as much heat output), but they run. Starting is usually the only issue with thin air. So if the burner starts, it will run. And temps are not as hot when high up so the fridge doesn't need to be as efficient at altitude anyway.

Carbureted gas engines are a little/lot more troublesome, depending on setup by manufacturer. My John Deere and Honda mowers run fine, but finding a gas weed eater or leaf blower that would run decently at 7500ft took several returns to the store. Even now, my propane soldering torch won't stay lit above 7000ft, but almost all camp stoves and home grills work just fine.

I had the same question when I read the same statement for my little 3.0 fridge in my a-frame, especially since we now live at 6,700ft (used to be at 7,600ft) and often go both lower and higher for camping. Dealer (Denver) said not to worry about it. As long as the spark generator is decently aligned, the fridge will light and run. Which has proved to be true (for heater and hot water heater, too).

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Old 11-22-2015, 12:26 PM   #18
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I guess the only way to find out is to try it. My old Winnebago Onan's altitude adjustment went to 0-10,000 feet. I think it's less on the new 4K Onan. I did have to adjust the air mixture on the Winnebago's Atwood water heater as it roared. The Suburban furnace was also noisy, but no way to adjust. Still worked fine, but that was a Winnebago. The new Forester may be different.
Just concerned about camping at Twin Lakes in Mammoth 8,600 feet, Tuolomne Meadows also 8,600 feet and Dorst Creek in Sequoia 6,800 feet and usually for 3 days.
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Old 11-22-2015, 01:51 PM   #19
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I have run both Dometic and Norcold propane fridges at high altitude and have NEVER had a problem with them or any of my other gas appliances. Normal camping for us is at 10,200 ft ASL and occasionally we'll camp at Heart Lake in Colorado which is at 11,300 feet.

Towing while running propane is a different story and has to do more with wind flow over the fridge compartment assembly and some campers don't have turbulent flow in that area and fridge runs fine while towing and some do have issues. Sheet metal barriers in front of the area may help get the fridge lit and stay lit while towing.

Here is what we do for our tow trips.

Run freezer/fridge overnight for it to get cool.

Freezer: All meats are frozen and put in the freezer tight. They will last an entire day's driving without RV fridge running though we do run ours on propane when towing.

Fridge: One gallon of milk and 1/2 gallon of orange juice frozen into a solid block will maintain decent fridge temps while towing if fridge jumps off line on propane. A couple of small frozen gel packs on top of cold cuts and other delicate items wouldn't hurt.

Don't forget to shut propane fridge off before entering as station and on certain tunnels/bridges per local rules and laws.

Having a backup plan with inverters and generators is a good idea is you have an issue. Most of time when an appliance won't fire up it it from rusty scaling on areas in direct contact with flame that may make it difficult for the initial spark jump needed to ignite the propane. Sometimes this scaling may fall off and partially obstruct air vent intake for the burner..you know the section where the air intake tube is adjustable to get the ideal amount of airflow into the burner section.
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Old 11-22-2015, 01:59 PM   #20
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Silverhawk,

If your fridge won't run at high altitude, there is nothing wrong with running your generator. Just put it far enough away so it won't bother you or others.

If you don't want to put such wear and tear on an expensive generator for small power draw, consider a cheap $89 harbor freight 800 watt 2 stroke generator. I carry it as a backup and almost always use it when I don't need a lot of power. It is perfect for running the heater all night if you don't have enough juice or running the fridge all day,e tc...etc... Best $80 bucks I have spent.

I used it yesterday to top off my camper batteries which I do each month. It was fun, I started teh generator, went inside, turned the heat on and got an awesome afternoon nap...the drone of the generator put me to sleep.

Have a backup plan but I'm sure your fridge will run just fine at altitude. If not, do some research on high altitude orifices for the fridge and ensure the burner orifice is clean on your fridge.
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