I put in a household frig in my fifth wheel, but of course when I unplug to move down the road it's off line. I noticed the newer fivers have household refrigerators and an inverter on board for when offline. Question is what size of inverter is needed for just this outlet and how do you wire it for part time use. Do you need a switch to allow the receptacle to go fro the inverter to shore power. Not an electrician and could use some help and ideas.

Here is link about this RV user changing over to a household type fridge to replace the RV type fridge...Residential Refrigerator for RVThis gives you a pretty good description in their eyes of what is needed to support just the Household type refrigerator. Please note the bottom line statement on what is required to just operate the Household type refrigerator."Best Power Setup for Off The Grid RV living with a Residential FridgeIf you don’t want to be forced to run a generator I’d say go for 800 amp hours of lithium, or 1200 amp hours of AGM and a solar array like our 960 watt All Electric kit from GoPower!. This should provide enough power to make it through 3 days of “normal” living (6 days if we are conservative) during cloudy weather without being forced to run the generator. Of course if there is full sun then we would be able to run almost anything as if we were plugged into the grid (we could even run our rooftop Air Conditioner for a couple of hours).Here’s the gear we recommend: 960 watt Solar Kit: http://amzn.to/1XWqmiD 800 AH of Lithium Battery (check out reputable brands such as Lithionics and Relion) 2000 watt (or larger) PureSine Wave Inverter: http://amzn.to/1Uvno74 Battery Monitoring Kit: http://amzn.to/1Uvp9Rt Automatic Generator Start (to ensure you don’t run your batteries down to low): http://amzn.to/21NAXgF Kill-A-Watt Meter: http://amzn.to/25r0Do1" This report is recommending a 2000WATT PURE SINE Inverter setup which will require a rather large battery system to operate it...Your question is going to be are you really ready for all of of this...After the shell shock of what is going to required then you will want to think about how to implement all of this into the RV just for the refrigerator.Two ways come to mind being to install a 120VAC receptacle coming from the 2000WATT Power Inverter just for the refrigerator or have a auto or manual way of switching the refrigerator 120VAC circuit between the OEM 120VAc system already in the RV and the now added 2000WATT Pure Sine Wave Power Inverter system. This will require a large current rated switching 120VAC type Power Contactor setup for automatic switching or a manual high current rotary switch setup. Both methods will require you to cut into the OEM wiring of the RV trailer to separate out the wiring required. To me the most simplest way would be to just install the 2000WATT Power Inverter and the required added batteries and high current required cables and just plug the refrigerator into the converter and leave it there. i.e. this will mean you will be always running off of the 2000Watt power Inverter just for the refrigerator. This of course will be a big waste of resources for the rest of the RV Trailer 120VAC appliances not working when not on Shore Power or Generator... I would rather run all of the other selected 120VAC appliances as well but that would require a larger Power Inverter setup... Bottom line is it all depends on what you want to do with it now that you have already changed out the refrigerator... Just saying and purely just my thoughts on the subject... I installed a 600WATT Pure Sine wave Inverter setup and supporting batteries and larger cables etc in my off-road trailer setup just to run a selected bunch of items to support camping off the grid like Home entertainment items, cell phone/computer chargers, lamps and fan etc and ran two 120VAc multi-tap drop cords to the areas for those items to plug into the Power Inverter when needed... being doing this since 2009 and it allows me to make it through the one day/night off the batteries but then I have to recharge my 50% charge state batteries to the 90% charge state to be able to do it all over again for the next day/night run off the batteries. My Ham radio hobby eats up alot of the batteries when being used hehe... Roy Ken

In order to answer your question, you will need to know the electrical specifications for the frig you plan to install. Unfortunately manufacturers don't typically publish the amp draw of their products. They do tell you average "KWhr" consumption for energy efficieny but that is useless when trying to answer your question.I recently converted my RV to a residential frig. When I finished the install, I checked the amp draw on the frig and it was 9 amps when the compressor was running. That is the number you will need to know.Inverters are rated in "watts". Watts is a product (i.e. multiplication) of Volts times amps. You know the voltage you have, 120v. If you can determine the amps, either by looking at the frig specs, or measuring it, or just guessing, you can calculate the watts. Mine was 9X120=1080 watts. If the inverter is serving the outlet for the frig exclusively, then a 1200 watt one would probably work. (Note that there will be a current "inrush" each time the frig starts, but that should work.) Most decent inverters have an automatic switch included that switches from the DC input to the 120 volt input automatically. You don't have to do anything to make it switch. Just connect the inverter to your batteries, and also connect the inverter 120V INPUT to your RV 120V system per the instructions provided with the inverter. When you plug into shore power, you will run the frig from that, and when you unplug, the inverter will automatically switch over to battery power. It is a seamless system. The next question will be how big your battery bank needs to be and that will be determined by how long of a trip you intend to make before you plug in. The frig is not going to run continuously so maybe go by the energy efficiency label. I just looked an an LG that estimates 432KWhr per year. There are 365 days in a year X 24 hrs=8760 hrs in a year so the frig will run about 432/8760=5% of the time. If you are going to drive 6 hours, that means it will run 30 minutes (.5 hours) during the trip. (your numbers will vary) In 30 minutes, the inverter will use 9X120X.5=.54KWhr during the trip. Your batteries will have an "amp/hour" rating. This rating tells you how many amps you can draw from the battery (typicaly for 20 hours) at a useable voltage. It is not good to totally discharge a battery. How long can you run a 9 amp frig on a 150 amp/hr rated battery before it goes to 50% is the real question. Divide 150/9=16 hours. Since our example says you will operate .5 hours, you should be ok. Notice I did not include any inefficiency in the overall system. 2 batteries in parallel will give you twice the capacity also.I have no doubt my comments will solicit further comments. Good luck with your project.

Why do people make it so complicated ???It's very simple,....All ya need is a PSW inverter capable of handling the power draw of the fridge, probably 800 to 1200 watts. Let the inverter power the fridge all the time. The vehicle's alternator will provide battery charging while not plugged into shore power. The RV's converter will provide the battery charging when plugged into shore power.If you ever dry camp, only one thing to say, Good Luck !

I run a small dorm fridge using an inverter. Solar charging keeps the batteries charged to provide the power.The easiest way to calculate inverter size and how much power the fridge uses over a period of time will be to use a Kill-A-Watt meter. The KAW will give you a readout in total watts used over a period of time. It will also show the typical draw of the fridge when running. Once you have the power measured, you'll need to get an inverter of sufficient size to not only operate the fridge but to overcome the Locked Rotor Draw of the compressor. The Tripp Lite inverters are known to endure a large initial draw and keep on chugging. Mr Wizard uses one with his 5'er. I use a Xantrex Prowatt 1000. My operating draw from the fridge is about 80W. Duty cycle is 1/3 -> 1/4. This all depends on ambient and how many door openings are involved. I initially tried a Samlex 600w inverter and it could not overcome the LRD. I have 300 AH of battery capacity and 235W of solar panel. Good luck with the inverter install.

A lot of bad info above... the 9 amps is times 12V not 120 so it's only 108W, not more than 1000W. You only need a 500W inverter to run a home refer. If Samsung refer it does not need to be a PSW as they use a DC compressor... otherwise you need a PSW inverter to run a motor efficiently. My 21 cuft refer draws 8 amps into the inverter when running... 96W and a duty cycle of less than 50 percent.If you are FHU to FHU camper you do not need to do anything other than keeping the doors on the refer closed if traveling 5-6 hours. If you go 8 hours then I'd freeze a gallon of water and put it in the refer section on those day.If you only boondock occasionally but put in a inverter I would run the inverter 120V to a compartment near the refer and a extension cord from the outlet that the refer is currently plugged into... to the same compartment so you can manually switch from shore to inverter power. Yes, you have to run the refer's power cord to the same compartment.If you boondock often then I would add 200+ AH of batteries (no you do not need 800 AH of additional batteries.) so you can go 24 hours before needing to run the generator to recharge the batteries. I would probably just run the refer off of a 500W PSW inverter all of the time.

Inverter install help | Good Sam Community

allbrandauto
Explorer
Mar 14, 2017
I just installed a res. ref. in my motorhome I used a zantrexs freedom xi 1000 watt pure sine inverter a little pricey at 495 dollars but had automatic transfer switch and a remote easy install and only needed inverter and batterys
road-runner
Explorer III
Mar 13, 2017
1 hp=745 watts. 1/2 hp = 372w. 372w/120v= 3 amps
That would be true with a 100% efficient motor with a unity power factor. In reality a 1/2 HP motor might be 70% efficient at optimum load, and have a PF of 0.75 (which varies with load). The math would be:

372 watts / 0.7 efficiency / 0.75 pf = 708 VA / 115 volts = 6.1 amps

The nameplate of a 1 HP motor I have says 13.6 A. A 1 HP motor is generally more efficient than a 1/2 HP motor. Motors of this size range generally do not have any PFC.
2oldman
Explorer II
Mar 13, 2017
larry cad wrote:
I still stand by my numbers.
You don't think something may be wrong with your measurements? It's hard to imagine the math being wrong by a factor of 3.
larry cad wrote:
A 1/2 hp, 1ph motor is rated to draw 9.8 amps at 115 vac.
Where do you find this rating?
larry_cad
Explorer II
Mar 13, 2017
2oldman wrote:
larry cad wrote:
My compressor is a 1/2 hp and draws 9 amps while running.
1 hp=745 watts. 1/2 hp = 372w. 372w/120v= 3 amps

You are talking math numbers, I am referring to National Electrical Code published ratings which are actual numbers obtained from real motors, including slip, and energy efficiency.

I still stand by my numbers.
2oldman
Explorer II
Mar 13, 2017
larry cad wrote:
My compressor is a 1/2 hp and draws 9 amps while running.
1 hp=745 watts. 1/2 hp = 372w. 372w/120v= 3 amps
larry_cad
Explorer II
Mar 13, 2017
MrWizard wrote:
larry the only time you could measure that much power is compressor startup
not even the defrost heating element in the door draws that much power
it would melt the plastic in the fridge

I stand by my numbers. A 1/2 hp, 1ph motor is rated to draw 9.8 amps at 115 vac. My compressor is a 1/2 hp and draws 9 amps while running. I don't see a conflict there. Perhaps you can clarify for me? The current I read with my ampprobe was just the motor, not the defrost heater which draws significantly less current.

Thanks
tbax46
Explorer
Mar 13, 2017
Mr Wizard
I'm only looking for enough power to keep it running while driving from one spot to another. The closest I get to dry camp is electric only sites.
MrWizard
Moderator
Mar 13, 2017
larry the only time you could measure that much power is compressor startup
not even the defrost heating element in the door draws that much power
it would melt the plastic in the fridge
Searching_Ut
Explorer
Mar 13, 2017
When Heartland was putting the residential refrigerators in firth 2015 models there was a known problem with the inverters overloading and tripping off. They were using 1000 watt inverters for refrigerators drawing 8.5 amps AC. Interestingly during our last RV shopping we were asking about the main reason for going residential. Every dealer we talked to said cost. Evidently many folks don't dry camp much anymore and when you get to the 18cf refrigerators they were saying it's almost $3,000 dollars wholesale for the norcold units, plus baffles vents, fans etc. and much cheaper for the residential unit and cheap inverter. Of course they don't give you a big enough battery bank to do this for off grid camping, so the actual cost difference will be different once you take care of that issue.
larry_cad
Explorer II
Mar 12, 2017
Ivylog wrote:
A lot of bad info above... the 9 amps is times 12V not 120 so it's only 108W, not more than 1000W.

Ivylog, I'm sorry, but you are totally incorrect. I measured the 9 amps with my AC amp meter, while clamped around the AC power cord of the refer. The AC power cord is fed with AC power produced by the inverter. That is what an inverter does, it creates AC power. My calculation is:

Amps X Volts = 9 X 120 = 1080 watts.

If you were to check the DC amps from the DC battery at the input of the inverter, it would be 90 amps (plus losses)

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