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Old 04-24-2004, 03:06 PM   #1
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DC to AC inverter for fridge while driving

What would be required to provide 110v ac to the refrigerator while underway?

What size inverter, from where could it be powered?

Is this a practical idea?
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Old 04-24-2004, 05:49 PM   #2
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Probably not practical. It takes 10 amps dc for every amp of ac power plus whatever loss from the inverter. You would need welding cable and an inverter that cost more than the frig. The batteries wouldn't last long if you used them, the alternator would be maxed out to keep up.

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Old 04-24-2004, 05:50 PM   #3
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The refrigerator element draws about 360W of 120VAC, so you'd need a 400-500W inverter, and be able to feed it with 36 amps from the tow vehicle alternator and battery. This is well beyond the ampacity of the charging line in most trailer plugs.

If you wanted to mount the inverter in the trailer, you'd need some mighty heavy battery cables coming from the tow vehicle battery to the inverter in the trailer, not only for the ampacity, but to keep the voltage drop ahead of the inverter down. You'd also need some way to disconnect them at the tow vehicle/trailer connection.

To minimize wiring thickness, it would be better to mount the inverter under the hood of the tow vehicle and run 120VAC cabling to a twist-lock socket mounted on the hitch, and then run a 120V line with a twist-lock plug at the trailer coupler, back under the trailer and up into the refrigerator compartment. I'd definitely run the 120VAC wire in conduit, both beneath the tow vehicle and beneath the trailer.

It's a lot more practical to run the frig on propane, but if all you have is a 120VAC compressor-type frig, the inverter is the only choice.
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Old 04-24-2004, 08:52 PM   #4
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as moe pointed out you would want to make the long run 120 volt.

if you were going to go that route you may as well just mount a belt driven generator under the hood! and not even have a inverter!

again, the cost would be higher than an lp fridge!

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Old 04-24-2004, 09:19 PM   #5
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welding cables and a generator...oh, and don't forget the conduit. Sounds like a nice two beer Saturday afternoon project.

At one time I had a pair of jumper cables made from welding cable; too heavy to carry in the trunk. Sounds like after adding the gererator and heavy cable, and refiguring the weight and balance, that I would have to leave the second and third case of guiness at home, along with the ten year old. I'd be better off getting a third aluminium LP tank.

As always, thanks for the education.

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Old 04-24-2004, 10:16 PM   #6
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well if you really want to do it....

ponz

take a look at auragen.

they even make one big enough to run your roof ac to boot!

http://www.aurasystems.com/

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Old 04-25-2004, 07:24 AM   #7
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I have seen two small (2kw) Honda generators hooked in series to power a travel trailer A/C. I believe they were getting 20a from each unit.

With these Honda units costing $800-1000 a piece, how does that compare cost wise to installing the generator directly on the tow vehicle engine?

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Old 04-25-2004, 08:12 AM   #8
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Why not simplify the whole project? If you have a pickup truck for a tow vehicle, and a Honda EU series generator, simply run the generator in the back of the pickup as you are underway. Then all you would have to do is run a small 120 vac extension cord to the trailer. Finding a way to run it directly to the fridge would be a good idea.
Compressor on my apartment style 120 vac only fridge in my A/S only draws 1.9 amps according to the sticker.
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Old 04-25-2004, 09:08 AM   #9
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My Honda EU2000 Parallel Setup provides 2 X 13.3A continuous, and 2 X 16.7A where Honda says you shouldn't go more than 1/2 hour. This will provide more than the trailer can use. For just the refrigerator, plus a crock pot simmering in the sink, an EU1000 would more than do the job. With an EU2000, you could temporarily turn of the frig and crock pot and use the microwave oven at rest stops.

I guess I could run them out of my truck bed but my 25' trailer cord comes out toward the rear of the 34' trailer, so I'd have to have an extension, plus I'd have to figure out some way of hanging the cord on the side of the trailer around toward the truck. You wouldn't be much better off with a 31' Sovereign.
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Old 04-25-2004, 09:08 PM   #10
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Moe, with your 2 EU2000 set-up, it produces more than 30 amps. Will this pop the 30 amp breaker & if not why? For instance, if you're running the AC & it cycles off, then the gens will be producing more than needed. Will they cycle down to less than the 30 amps? I have one 2000 unit & I hesitate investing in another, till I'm sure of what I'm doing.
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Old 04-25-2004, 09:43 PM   #11
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My setup has the potential of providing more than 30A if more than 30 is drawn from it. So does a campground outlet, be it 30A or 50A.

At some point, the further beyond 30A combined with the greater beyond 30A, the main input breaker to the trailer will trip, just as it would on campground power.

The generator doesn't push current into the trailer whether it needs it or not. The trailer draws as much current as it needs from the generators, or campground power, to a point. On Eco-Throttle, the generators speed up or slow down in response to the demand for current, however, they can also both be run full speed, and provide only that current that is demanded.

I can run the AC, the microwave, and the refrigerator on AC at the same time, if the batteries are charged and the converter isn't drawing a lot. If I get stupid and turn on the AC, microwave, and water heater electric element at the same time, I can overload the 30A main breaker, whether it's powered by campground or generators.
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Old 04-26-2004, 05:47 AM   #12
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two eu2000 gens plus wiring total cost $2000?
how much to mount the gen on the truck engine?
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on edit; found an EPA aritcle http://www.epa.gov/otaq/retrofit/idlingtech.htm

"No maintenance is necessary. 1-2 days to install. A 3-year warranty is standard and a 5 year expanded warranty is available. Cost: $7,000"

I'm not sure what model or if installation is inlcuded.
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Old 04-26-2004, 06:09 AM   #13
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You would only need ONE EU2000 to run your fridge. Those Auragens are much more expensive than a single EU2000i. On my A/S, I can snake a bare cord up through the bottom fridge vent on the belly pan and up to the truck fairly easy. That way you do not have run an extension cord all the way to the back of the coach.
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Old 05-10-2004, 05:46 PM   #14
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OK - up to 25 continuous amps (3000w); all for less than $630.

http://www.americanvan.com/catalog/s...m?FamilyID=105
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Old 02-28-2015, 03:54 PM   #15
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Reasonably practical.

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Originally Posted by the ponz View Post
What would be required to provide 110v ac to the refrigerator while underway?

What size inverter, from where could it be powered?

Is this a practical idea?
The Inverter is the easy part. A 500 or 600 watt unit would easily handle the load. The problem is that you need ten times the current to operate the fridge at 12 volts through the inverter. It will draw about 20 amps from the batteries. At this current level the Inverter will have to be wired directly to the batteries through a 30 amp breaker (separate circuit from your existing breaker box).

This level of current will quickly run down your batteries if the engine is not running. So it is only usable while driving and not an alternative choice for boondocking. The early 3-way fridges were only useable on 12 volts when the tow vehicle engine was running which kept the batteries charged.

You need to set up some protection circuit to disable the 12 volt inverter in case you forget to switch the fridge to propane or shore power after you park. With a 3-way fridge it just switched automatically.

Inverters are relative cheap so the cost is not a big factor. You could also include an outlet socket so you can run a TV or chargers when boondocking.

Forget about running a 110 VAC line from an inverter installed in your tow vehicle. Yes, it is a relative low current level, however it is not safe having that level of voltage on your tow cable. I am pretty sure it is illegal to run this voltage level on the RV to tow vehicle cable.
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Old 02-28-2015, 05:15 PM   #16
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Notes:
  • Honda EU2000i output = 13.3 amps (full load).

  • Two EU2000i's connected in parallel = 26.6 amps total (calculated)

  • Propane refrigerators do NOT use much fuel. In 78 days of camping full-time last spring (mild rainy weather in the Pacific northwest), one of our 30-pound propane tanks only needed refilling once; and this included using the refrigerator 24/7, heating hot water for showers, and occasional furnace usage for a couple of hours at night.

    In my opinion, the extra cost to power your refrigerator with electricity while underway would never be recovered, compared to using propane. However, if you already own (or plan to buy) a generator for other reasons (e.g., boondocking power), using 120 VAC for your refrigerator may work for you.
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Old 02-28-2015, 05:30 PM   #17
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Quote:
Originally Posted by WayWard Wind View Post
Moe, with your 2 EU2000 set-up, it produces more than 30 amps. Will this pop the 30 amp breaker & if not why? For instance, if you're running the AC & it cycles off, then the gens will be producing more than needed. Will they cycle down to less than the 30 amps? I have one 2000 unit & I hesitate investing in another, till I'm sure of what I'm doing.
Best,
Circuit breakers trip because of excess draw on the electrical supply, not because of the electrical input potential. You can use a 50 amp adapter to connect your 30 amp trailer to city power. I have been at places that only have 50 amp supply. Another time the 30 amp supply was not working so I connected to the 50 amp plug using a 50 amp to 30 amp adapter.

I would not try to exceed 30 amps of draw, as the breaker system of the trailer is set up for 30 amp max.

Look at it this way. You can plug a small, LED bulb into a 15 amp circuit in your home, and it will work just fine, but if you plug in and turn on three electric fry pans and a coffee maker into that same plug, you will blow the circuit breaker. Too much draw.
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Old 02-28-2015, 06:28 PM   #18
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Depends on your fridge, the old Dometic in our Argosy the heating element draws 120 watts and we are running it on an inexpensive 800/450 watt inverter so figuring inefficiency losses ect; it may be taking 13 to15 amps from the battery/alternator. Thats enough to run your battery down pretty quickly if the engine is not running in the tow vehicle.
Two years ago we had a little Toyota motor home with the same setup and did a trip from home (Florida) to Alaska and back a bit over 14000 miles,ran all over Alaska even north of the Arctic circle, fridge worked perfectly and still is as i sold it to neighbor and we are still friends! Would take alot of typing to explain how to do it pretty simply,so if you are interested send me a PM and i will go over it with you.
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Old 03-14-2015, 03:51 PM   #19
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360W @ 120V us is only 3 Amps. what am i missing here? the info i have says, start up of the frig draws 4.5 Amps at 120 V and from that point you have the fan running which is not much of a draw.

also keep in mind that a circuit rated for 30 Amps is only going to provide 24 Amps at full load, 80% of the rating is the standard.
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Old 03-14-2015, 05:28 PM   #20
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It's 3 amps at 120vac but to provide that 360 watts through a theoretically 100% efficient inverter will require 30 amps of 12vdc. Most standard battery banks won't be happy doing that more than a couple of hours.

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