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DM2852 inverter size needed


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So i've just run out of propane I guess. I thought dometics ran on 12v. To my surprise its a 2 way 110v OR propane not a 3 way 110v,12vdc, or propane. 

I rigged up an inverter, 400 watt constant 800 w peak. In the picture I have the fridge's  original 12v wire going to the inverter and routed two 18 awg wires from the inverter posts to the 12 v input on fridge.

Peak power from the fridge seems to be too much for the inverter, once the ac compressor kicks on instant overload warning. Will this set up work once the fridge is at temperature?

Anything look or sound unsafe? Perhaps inverter being so close to the propane tube?

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Edited by Burgboy
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Short aswer is No.   The dometic 120V heating element is 1500W.  It does not have a compressor. Even with a bigger inverter you'll need a hell of a battery bank for any reasonable amount of time off the grid.  Propane heat is much more efficient.  If you need to run a fridge on the inverter, get a 120V fridge.

Edited by toastmn
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There is no compressor.  That is an absorption fridge.  It must boil the chemical media either with a propane flame or a 110 volt heating element.  That 400 watt inverter is much too small.  It would take at least 3 times that much and would kill your batteries in a short period of time.  Absorption fridges requires either shore power or propane for heat source.  They are just not practical on battery power.

Richard

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5 minutes ago, hex_nut said:

There is no compressor.  That is an absorption fridge.  It must boil the chemical media either with a propane flame or a 110 volt heating element.  That 400 watt inverter is much too small.  It would take at least 3 times that much and would kill your batteries in a short period of time.  Absorption fridges requires either shore power or propane for heat source.  They are just not practical on battery power.

Richard

Thanks I didnt know what an absorption fridge was. Im on shore power at the moment. Any idea where to check to see if its working? I think my readings here is just residual temperature from before i ran out of propane

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The heating element is directly above your inverter in your picture.  2 two heavy gauge wires. Its insulated and protected from the elements.  It takes a while, make sure the coach is level, and has good airflow.

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If you are on shore power and your fridge is set for electric power source it should energize the 110 volt heating element.  The overload you were receiving on the little inverter was likely when the heater energized.  If you have a volt meter, you can check the power wires to the heating element to insure your are getting 110 to 130 volts alternating current (110 is minimum, 130 is maximum).  The heating element is installed inside that rectangular tower just above your inverter in your picture.  Even if it is working correctly, it will take a number of hours o get that fridge cool again.  That is just the way absorption fridges are, that is why many people (me included) remove them and install compressor fridges.  (As well as to remove the fire potential.)

Richard 

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Just now, Old Dog said:

I must be missing something. Way don't you just refill your propane tank?

I bought a 5 gallon from the gas station... cant figure out how to put it in my coach tank

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You call a propane service company. They come to you with a propane truck and fill your tank as you stand and watch. They charge by the pound. A full tank should last at least 3-4 weeks of constant propane mode use.

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Just now, Old Dog said:

You call a propane service company. They come to you with a propane truck and fill your tank as you stand and watch. They charge by the pound. A full tank should last at least 3-4 weeks of constant propane mode use.

Sounds expensive. I'm fulltiming in a 1999 making $15 an hour in LA

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That is a dangerous combination. The 18 ga wiring(12v) is wY too small for the current requirements to run your 2 way fridge on electric. Also the inverter is way undersized. You would need one rated at 1500w continuous to support the fridge but you will need 2 ga or larger wire between the batteries and the fridge. Go get propane if you are not on shore power.

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26 minutes ago, 1nolaguy said:

That is a dangerous combination. The 18 ga wiring(12v) is wY too small for the current requirements to run your 2 way fridge on electric. Also the inverter is way undersized. You would need one rated at 1500w continuous to support the fridge but you will need 2 ga or larger wire between the batteries and the fridge. Go get propane if you are not on shore power.

Listen to Loel, what you are trying to do can over load your wires & may start a fire.   Turn your frig to elect and you should feel the box above your inverter start to warm  up

If it's getting warm or hot back there, fridg should start cooling.  As already stated thr fridg needs to be pretty level or it may destroy itself,  and they are slow.

Are you sure you are out of propane?  Does your cook top work?

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2 hours ago, toastmn said:

The dometic 120V heating element is 1500W. 

Not hardly.  I have the larger RM1350 where the heating element is 420W.  On shore power my entire coach only draws 4A with the fridge in elec mode. 

The DM2652 element draws 325W, which is over 27A from a 12V source.  It's not the inverter that's undersized but the wiring feeding it.  You'll need 12 ga wiring all the way to the battery for 30A service.  Don't forget to fuse it.  This much current will drain your 12V batteries in a short time (ok, hours). 

Sounds like your best bet is to refill that propane tank and keep your 12V battery charged (fridge draws about 2A in propane mode).  Is that possible? 

Once you get it going it will take a half day to chill down to temp.  If outside temps are hot (90F+) the inside of the fridge may never get down to temp. 

Absorption fridges like the Dometic will last a long time *IF* they are kept level.  Out of level and the interior tubing will corrode, a little here, a little there, until pinholes allow the refrigerant to escape (ammonia smell).  However, if that fridge is really 23 years old and not cooling once you get the power / propane sorted out it may be time for burial.  Sorry. 

Good luck and keep us posted.

- bob

 

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5 hours ago, cbr046 said:

Not hardly.  I have the larger RM1350 where the heating element is 420W. 

- bob

 

I stand corrected, the heating element in question is 325W.  Either way,  your wire is undersized.   You'd be better off using a regular extension cord and relocate your inverter (with bigger wires).  Still not going to be good enough for running a fridge off the grid..

You can buy a kit to use an external propane tank.

https://www.amazon.com/Camco-59125-Propane-Brass-Hose/dp/B007HG7N3C/ref=asc_df_B007HG7N3C/?tag=hyprod-20&linkCode=df0&hvadid=312142484282&hvpos=&hvnetw=g&hvrand=8539811518724470973&hvpone=&hvptwo=&hvqmt=&hvdev=m&hvdvcmdl=&hvlocint=&hvlocphy=9019630&hvtargid=pla-570321219104&psc=1

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Coming in late.  From a Moderator's perspective....we need some facts before answers are given....

BURGBOY...

What is the MODEL of the Dometic. There is a "Plate" or data placard inside the Refrigerator. That will give you the MODEL number. It will ALSO list the Amps or the Watts. That is needed before you try to figure out how to run it off an inverter.

Next UP. You are Full Timing.  If your Electricity is provided in your lease or rental, then WHY are you running on Propane? Typically, based on a LOT of history and posts here and on the original site, Propane is the MOST expensive way to run the Absorption units....  Something to consider. Will address that later.

I blew up your picture trying to get a Dometic model number and could not. If you would provide the Model number....at least we could look up the manual and specs and determine the EXACT Size of the Heaters....otherwise, the guesses are about as good at the information provided....

Electricity and DANGER...  If, ASSUMING, your Dometic is 325 Watts. That would be less than a 3 amp draw on a 120 VAC AC line. BUT....if you feed it through the inverter, that would be 27 Amps.  That means you should have #10 Wire. OPPS....you have a 400 Watt Inverter. It has a PEAK Load of 800....as in a "startup". Common sense and CODE requires that you run a service to it that will protect the wiring.  800 Watts - Peak divided by 12 equals 67 Amps....  (Watts = Volts X Amps). That is a #6 Wire. Obviously, you have a fire hazard. At the minimum, if you sleep with a smoke alarm and a fire extinguisher, by your bed....you need #10 service. I am sorry for being direct....but you need to understand how to select wiring and make modifications to keep you and your family or whomever, as well as your neighbors SAFE.  

Propane 101.  For you education. Propane is Liquified Petroleum.  As in it is pumped under high pressure and that high pressure keeps it in the LIQUID STATE.  What you burn is the vapor from the TOP of the tank.  The internal tank pressure, on a hot day will approach 200 PSI. Thus, tanks have thick walls. 

You purchased 5 gallon tank. That tank is filled or pumped as a  "Liquid" (think COLD water) The LP (Propane) in the tank is under pressure to compress it so you store it as a liquid. It begins to Vaporized (turn into a burnable gas) at MINUS 44 Deg F. That is why the sides of a tank, with heavy use, will frost up.  The pumps take the liquid out of the big storage tank and pump the liquid into a tank.  Your 5 gallons is actually a 20 Pound Tank....and it was only filled to 80% of the capacity or about 16 pounds to allow for expansion. 

Bottom LINE....there is NO WAY to "pour" the propane from your small tank into your big tank. You will spend WAY MORE on filling a small tank and toting it back and forth than having a Propane Service periodically fill your larger tank.  

You also need to understand that the Tank Pressure, at up to 200 PSI can NOT be burned. You have a large Regulator on your big tank and it is plumbed directly to your refrigerator. It is NOT recommended, unless you are a qualified plumber and understand pressures and gas connections that you make modifications. 

The Camco KIT suggested is $65 or so. You have to TURN OFF THE PROPANE TANK VALVE.  Then remove the POL or the fitting. It is a LEFT HANDED THREAD. Then you put in the "T". You then attach the MH's Regulator (that has the POL) to the adapter or T. Then you can use the 5 gallon tank.  BUT, most folks only do that in an emergency when they need to cook or heat water.   As you have figured out...the tank method is very expensive....and costly to operate.

https://www.camco.net/brass-tee-w-4-ports-w-5-hose-clamshell-59125  Look at the pictures....

Bottom Line...Your wiring is undersized....BIG TIME. Using Propane to run the Dometic is more expensive....and in today's inflated fuel and oil prices....maybe OUTTASITE.  You are dealing with an Engineer that did power projects and analyzed utility bills for several plants and they were spending over a Million per month...and that was electricity but I also looked at fuel oil, natural gas and propane and rans scenarios on converting.....so I can do a quick calculation for you...

MOST RV Refrigerators (size unknown) are SUPPOSED to be able to run for 12 Days on a 20 Pound cylinder. That cylinder is only filled to 16 Pounds of Propane. That amount of propane is equivalent to using 100 KWH of electricity. The national KWH Rate, per our Government, is $0.1447 or call it $0.15. So, the equivalent Electricity costs for that 100 KWH of electricity is $15.00. How much does it cost to get your 5 pound tank filled?  I'm betting it is a bit more than $15.

AND, you have to spend $65 just for the privilege of paying more to keep your food cold.

Hope this makes sense....Look at the options and then decided what you want to do. BUT, if you go the Battery Route....you need some big wire to be safe.

 

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  • 2 weeks later...

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Got the Camco installed thank you very much... I've only had nonperishables in for some time now. So I actually have 2 sets of 18g wire going from inverter to 12v. AFAIK  the 12v is only used for ignition

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Close up of the two sets of wires, just something field expedient until I get a real job.

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53 minutes ago, Burgboy said:

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Got the Camco installed thank you very much... I've only had nonperishables in for some time now. So I actually have 2 sets of 18g wire going from inverter to 12v. AFAIK  the 12v is only used for ignition

20220712_151812.jpg

Close up of the two sets of wires, just something field expedient until I get a real job.

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20220712_152403.jpg

 

53 minutes ago, Burgboy said:

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Got the Camco installed thank you very much... I've only had nonperishables in for some time now. So I actually have 2 sets of 18g wire going from inverter to 12v. AFAIK  the 12v is only used for ignition

20220712_151812.jpg

Close up of the two sets of wires, just something field expedient until I get a real job.

20220712_152257.jpg

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20220712_152205.jpg

20220712_152403.jpg

Looks like the Camco is installed correctly.  Do a soap and water test on the two high pressure fittings.

Yes, the refrigerator only uses 12 VDC for ignition.

To keep this on topic and prevent needless comments and regurgitation, your original post was that the inverter you installed would NOT provide the power to allow you to plug in the Dometic’s AC line to it.  That does NOT CHANGE.  The 18 gage wire is only rated for 10 amps.  If you double or run two 18 gage wires, that is 20.  The refrigerator circuit MAY be fused at 20 or probably only 15 amps.  So the wire size with two will only give you 15 amps.  At 12 VDC, that is only 180 watts…AMPS times VOLTS.  Folks have guessed and also asked for WATTS.  Your data plate shows 440 watts or 15,000 BTU/Hr.  That is the GAS BURNER CAPACITY.  Gas refers always cool better on propane as the heaters are less.  Your heater(s) are rated at 325 watts, (2.77 x 120] so it doesn’t chill as well on AC.  In LA, you probably need to use Propane for optimum cooling.  Got all that?

FACTS.  Even with TWO pieces of 18 gage will only, without blowing the fuse or melting the wires, supply  55% of the needed current or watts for the AC a heaters If you use the aux inverter to try and run the Dometic on AC or the 120 VAC heaters, it AIN’T gonna work.  Pure and simple.  Do NOT plug in the Dometic 120 Line cord to the Aux Inverter and risk a fire.

You CAN use the INVERTER for AC to the Dometic, but ONLY if you run a #10 wire, fused, inline at 30 amps from the Battery.  Odds are, you can run a shorter lead and drill a hole and clean off the paint to the Chassis Frame….otherwise run a #10 ground to the battery.

Hope thus clarified it for you.  Use Propane from the tank, but be aware that is costly and try to get your big tank filled.  You will probably get 10 to 15 days from the 5 gal or 20 pound cylinder.  NEVER, EVER use the Duralast inverter for AC to the Dometic until you upgrade and replace the wiring.
 

That’s it.  Thanks for the update. Be aware of my and other posters concerns and that we are trying to help you get through this and stay safe.  As a Moderator, my job is to make sure you have facts and understand as well as to prevent folks from guessing.  Good Luck.

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