Ok so my new (ha) old 1966 Barth only had AC power at the moment. Heres my question... If I install a deep cycle batter with 100Amp Hours, connect it to a 2000 Watt inverter (or larger?) - couldn't I plug my trailer in, assuming I don't overload it, say just run my refrigerator when I am moving from place to place? What am I missing here?

Teach me Obi Wan(s)?

it would be easier to run it off propane. In any event, most deep-cycle batteries are around 200+AH, and you would need only a 500W inverter, as the electric element for most reefers is ~300W.

So the logic of this would work though right? Meaning do I need anything between my inverter and my plugin for the trailer and/or plug frig directly into inverter. I saw some articles about needing a fuse or electrical box between? Maybe I am over thinking this...

Thank you Rusty

You need a battery on the trailer, to power the inverter, even if charged by the connection to the tow vehicle. Most inverters have protection on both the 12VDC (fuses) and 120VAC (circuit breaker). You don't want the trailer connector to be throughputting 25A.

Why are you resisting the logical solution, which is propane?

Propane refrigerators are much more expensive to buy than the average 110V ones but are much more convenient. This is assuming you have propane already set up in the trailer. The frig will run for a long time on very little propane.

The difference in cost would be offset by the expense for batteries and inverter. OTOH you would have both 12VDC and 110AC available for other uses. However, even large batteries cannot run the frig for more than a day or two. Solar panels would help extend the battery life but again, more expense.

Propane refrigerators are one of the causes of RV fires and many RV dealers and insurance companies are trying to run them out of existence.

OTOH, Servel type gas refrigerators have been around for 100 years and I believe the risk is minimal if they are well maintained, inspected and cleaned regularly.

So, it depends on how long you need to run the frig off grid, and whether you need the 12v and 110v for anything else.

Having both coaches with fridges that don't have propane, Class C is a 12v/120 that was original. Class A has 120v household unit. I can run a few days off batteries and inverter depending on weather, but will wipe out 12v batteries.

My solution was to just make ice boxes out of them. I make sure every thing is pre chilled first. A small metal pan on top shelf with ice and a D cell powered fridge circulating fan works great.
I freeze 2-1/2 gal. milk jugs when 120v is available and then place them in the pan for ice box. Keeping food in the fridge.

For bottle water, beer and other drinks I use a cooler with ice that I store in the shower.

Most of our use is over weekends. I have made a 12 day trip using this method. IMHO the cost of a few bags of ice far out way the cost of batteries and inverters few times I boonedock.

A small Honda inverter would be my other choice for keeping fridge running while traveling.

We really need to know what type of reefer Jan has.

Use rock salt in your ice in your cooler - keeps your drinks colder
http://www.woodchuck.com/blog-...-the-perfect-cooler/

Ok yeah I don't have any propane on this trailer, I would have to start from scratch on that and I am not really needing to be "off grid" for any length of time. I have a 500 watt fridge now. It is not an RV fridge - its just a small regular fridge (Retro Daewoo in Turquoise, totally adorable if not practical).

So I am not resisting propane- I just think I can get by on this solution. I guess I would rather get a deep cycle battery for $300 and an inverter to have some power for say a 8 hour day out at the beach (redneck rivera maybe ha or for a 10 hour drive to my destination, wherever that might be.

What does this mean Rusty? "You don't want the trailer connector to be through putting 25A"?

Thanks guys!!

500W is ~4.2Amps @120VAC. An inverter putting out 500W @12VDC is 500/12=42 Amps. The typical converter is 80% efficient, so it will draw at 500W, 42/0.80=52.5A Figuring the compressor runs 1/2 the time, ~25A to keep the battery charged. This would require a 10 ga. wire if the tow vehicle is used to charge the battery..

Two 12V deep-cycle batteries in parallel would provide about 400AH, enough to run the reefer for several hours, using a conventional charger to recharge from shore power.

Ah OK Rusty got it - I did not know you had to use 12V to calculate conversion using the inverter to get the Amps used - I was using 4.2amps thinking I could get a 100AH batter and run it for 8 hours. With the conversion, it will only last maybe 2 hours.

I will probably add solar to keep the battery(yes) charged at some point. Meanwhile I may just use some of the "cooler" ideas for the time being. Until I become an experienced RVer, and can boondock for days -- thanks!

I am not sure about all these numbers for amp hours. I can tell you this. Going down the highway, I run my refrigerator on 12 Volts DC. Once I forgot to switch the refrigerator back to propane when I stopped. It was not far into the evening when the lights began to get pretty dim. The batteries I have for house batteries are two AGM (Advanced Glass Matt,) The batteries are the 8d. Each of which is about the size of 3 car batteries. If I do recall the batteries are 240 AH each. All the math aside, coolers and ice packs are your best bet. Doorman knows best, and Rusty and Steve present a excellent technical argument.

As so often the case a one off situation is not a good idea to draw a conclusion from what was observed.

Actual battery usage and capacity depends on many things.

1. Battery charge at the start of the time. Driving, even long distance driving does not fully charge batteries, 80-90% at best. Unless a 3 stage regulator for the alternator is added, this will always be the case.

2. Battery maintenance. Although AGM are "maintenance free" they do require to be maintained by a smart battery charger if sitting unused for a period of time. AGM batteries lose charge of about 1-3% per month.
All batteries should be maintained but it is especially needed for AGM types to prolong their useful life.

3. Age of the batteries. AGM batteries do not last as long as flooded batteries. They are getting better but this is still the case. If AGM batteries are ever discharged completely they may not come back. Even if they do they will not come back to rated capacity.

4. it is amazing how much other "stuff" runs in the background. Lights, even LED lights when there are lots of them add up. LED TVs even in standby mode will draw a few amps at 12 volts input to the inverter.

I have 6 golf cart batteries all tied together about 625 rated AH. After a full days driving, with a three stage alternator, I will have nearly 100% charge. By the time I go to bed, voltage will read 12.6 VDC, the only things running are 2 TVs in standby, video converter, router and inverter. By morning the battery voltage will be down to 12.3 VDC.

If I shut off all 120 volt breakers the voltage will be down to about 12.4VDC. If I switch off the inverter, house batteries switched off line, the voltage will be slightly down to 12.5-12.6VDC. All inverters still draw power from the batteries even with no load drawn from the inverter.

Ohm's law,(E=I*R) V*A=W, W*H=WH and more are all accurate but depends on input data being accurate, NOT assumed