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Inverter Question


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My trailer has two group 27 (I believe) Marine Deep Cycle batteries.  I do not have a generator on truck or trailer.  I would like to run my fridge on an inverter as we travel between campgrounds.   That time period before we would be back on shore power would almost always be less than 12 hours.  I do not want to run on propane while traveling.  My question could I do this on two batteries and what size inverter just for fridge, no other loads.

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From the propane statement, I am assuming you have a typical RV refrigerator?  If so, the electric heating element is going to draw a lot of power.  The first thing you need to do is put a Kilowatt (or other measuring device) on it for a few hours during the heat of the day and see how much power it draws per hour.  With that information, we can give you a much better answer.

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If you were to go to a residential refrigerator, easier to answer in my opinion. I think Chad has a simple 1000w Magnum inverter that runs his refrigerator. I have the same inverter and can go 8-10 hours on the two interstate batteries. If I hooked up my power to the trailer plug, I assume I could go indefinitely if it was charging the batts off the truck alternator while going down the road. 

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Carl, Our recent purchase came with a Xantrex Freedom HF 1000 watt inverter running on 2 6v batteries.  It should theoretically be fine for 12-14 hours with a whirlpool fridge without the truck supplying any charge to the RV batteries.  I say theoretically because our "New" batteries are cooked.    

When we had our Carrilite, I ran a cheap Harbor Freight inverter and a 5cuft freezer in the basement with no issue.  The truck does supply a 14v charge but at a low amp.  (14gauge wire)

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RV fridges on electrical power can pull a good electrical load. Residential fridges are much better on electric. If you don't ever plan to boondock, you may be better just upgrading to a residential fridge to have all the benefits of it if you don't plan to ever run your current one on propane and that will allow you to size the inverter and batteries just for the fridge. 

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My last few rvs that had just a single wide 2 door refers by Dometic and Norcold took about 22ah to run on 12v with losses through the inverter. We now have a double wide 4 door Norcold and is a pig! 43ah to run it....must have 2 heating elements? I ran the smaller refers on the inverter all the time enroute, but the larger unit just draws too much current to get charged from the truck without punishing the batteries.

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7 hours ago, CrazyCooter said:

My last few rvs that had just a single wide 2 door refers by Dometic and Norcold took about 22ah to run on 12v with losses through the inverter. We now have a double wide 4 door Norcold and is a pig! 43ah to run it....must have 2 heating elements? I ran the smaller refers on the inverter all the time enroute, but the larger unit just draws too much current to get charged from the truck without punishing the batteries.

That’s what we have, a single wide Dometic.  It is fairly new and works great so don’t really want to pull it out and replace at this time.  So what is the math to determine inverter size, battery size, and time I could run on inverter alone at 22ah?

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A pair of 27s is about 180ah or 90ah usable without punishing the batteries. That leaves about 4 hours of run time assuming you get no charge from solar or the truck to help.......not much time there. That might just cover it assuming the refer is cold before you leave and you don't open the door in transit.

What about mounting the inverter on the truck and running the 120v line back to the trailer? Much less loss that way.

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