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Old 11-12-2014, 08:39 PM   #1
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1000w inverter for Dometic Rm3762

My wife and I are new Airstreamers with a 2014 Eddie Bauer 25. Our TV is a 2014 Tundra 5.7L.

We are loving the AS!

We sometimes take long days on the road to get where we are headed and despite taking the advice I've read here about keeping food cold (load and chill the fridge before leaving, add ice packs in the morning, etc) at the end of a long day the fridge is typically above 50 degrees. Too warm to keep food fresh.

I'm considering two options and figure this is the place to get perspective on which I should use.

1. Run with LP on to keep the fridge running (understanding the requirement to pull over and shut down LP before gas stops) or...

2. Add an outlet on the inverter circuit to the access space for the fridge mechanicals where there is already an outlet for shore power. Before hitting the road I would replug the fridge from the existing outlet to the new inverter outlet and turn on the inverter.

As background, our trailer has a factory 1000w inverter, the fridge is a Dometic RM3762 and the Tundra has a 170 amp alternator. The inverter circuit runs through the space behind the fridge and above the panel in which the existing outlet is mounted and there is about 2' of extra wire. It's as if the factory said "place another inverter outlet here, using this extra wire".

The practical side of me says "try it in the driveway with an extension cord from en existing inverter outlet... what's the worst that can happen?" The cautious side of me says "if it was that easy, the factory would have spent the 10 minutes and one additional outlet to install one there".

I figure one of you might have already learned what I'm struggling to answer. Any thoughts will be appreciated.
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Old 11-12-2014, 09:10 PM   #2
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Doesn't your fridge run on 12 volts also?
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Old 11-12-2014, 09:10 PM   #3
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The heating element in the refer will require in the neighborhood of 300 watts. When you factor in the losses thru the inverter. Typically 15% loss. Then calculate the current draw on the battery bank. You are looking at 385 watts: divided by 12 volts: equals 32 amps, round numbers.
Even though you have a high capacity alternator. The wire size and length between the TV and coach will work against you.
It's not to say you can't do it. But it is much more efficient to leave the refer on propane. From both the battery power efficiency and the heating element.
The propane heat source has a greater capacity when compared to the heating element. IMHO
I am not aware of any requirement by law to shut of the refer when fueling. Except for some tunnels on the east coast.
You are much more likely to ignite the fumes when refueling with the static discharge of your body created when you slide off of the seat. Thus the placards at fuel stops warning about static charges.


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Old 11-12-2014, 09:18 PM   #4
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I would run with the propane on if I had a propane fridge but I don't.

I have a residential fridge that uses a compressor. I run this through my inverter when traveling. My truck keeps the battery up no problem.

This said, I think my 10 cuft fridge uses about 1/2 the electricity that your RV refrigerator uses.


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Old 11-12-2014, 11:46 PM   #5
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We have a 2013 Flying Cloud 25FB with the same fridge. We have an aftermarket inverter/charger and 435 watts of solar power. We also have a display that shows the current drain/charging usage of the batteries, and the output of the solar panels.

The fridge draws about 31-33 amps of current (from the 12 volt system) via the inverter. Your Tundra will not deliver that much current to your trailer.

We do run our fridge via the inverter when traveling, but it only works for us because of our large solar installation. Around midday during the summer, the panels put out about 25 Amps. My tow vehicle can contribute 8 amps, which means under ideal circumstances, running the fridge does not draw down the battery. Earlier or later in the day, the solar puts out less, and we do draw down the battery. When the fridge cycles off, the batteries get charged. At the end of a sunny summer travel day, we are down less than five amp-hours. In the fall, we are down more, perhaps 20-25 amp-hours.
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Old 11-13-2014, 12:08 AM   #6
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*IF* your tow vehicle switches off the 12v power on the 7-bin umbilical connector, I think your refrigerator will automagically interrupt the propane operation for a while when you turn off the ignition. I confess that this is total hearsay on my part, as I have an ancient 'fridge with no 12v components. I generally leave it running when I can find an "RV pump" where the trailer isn't near another gas pump while I'm fueling the truck (as it would be if I pull up to the 2nd pump in a regular big fuel stop by the highway. My fridge's air intake is on the opposite side from my truck's fuel filler, though, so there's a little distance there anyway.
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Old 11-13-2014, 05:25 AM   #7
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Thanks for all the answers! I feel like Santa came overnight while I was sleeping.

To GeocamperAS: This Dometic model is 2way, LP and 120v.

To all: I'll stick with LP underway for now. It seems to be the proven solution.

We're hitching up this morning to head to Mt. Dora, FL for the weekend. No gas stop needed for that trip and no risk of tunnels since the early attempts to put tunnels in this part of Florida were rapidly reclassified as canals, so I am looking forward to arriving with fresh food still fresh.

Thanks!
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Old 11-13-2014, 06:05 AM   #8
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Quote:
Originally Posted by DKB_SATX View Post
*IF* your tow vehicle switches off the 12v power on the 7-bin umbilical connector, I think your refrigerator will automagically interrupt the propane operation for a while when you turn off the ignition.
If we're talking about a trailer: Err, no; otherwise it wouldn't work while you were camping and unhooked from the truck. Well, I guess if the trailer didn't have a battery it would do this, but that's not something we should be doing anyway.
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Old 11-13-2014, 09:56 AM   #9
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If we're talking about a trailer: Err, no; otherwise it wouldn't work while you were camping and unhooked from the truck. Well, I guess if the trailer didn't have a battery it would do this, but that's not something we should be doing anyway.
As I said it's hearsay for me... from reading these forums, though. It may well have been someone with a motorhome writing about it, or it may be a feature Dometic no longer provides. It would require an extra wire to to fridge from the +12v pin wired such that it could detect interruption of 12V there. It would probably offer one more way for the fridge to break, though.
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Old 11-13-2014, 10:22 AM   #10
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You can run the fridge on LP while traveling. It automatically shuts off for 15 minutes or so for fuel stops. I don't know how it knows- maybe when the truck's ignition is shut off the converter knows?
We've been running the fridge on LP while traveling 4 years - food keeps at 36 degrees-
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Old 11-13-2014, 10:46 AM   #11
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Quote:
Originally Posted by DKB_SATX View Post
As I said it's hearsay for me... from reading these forums, though. It may well have been someone with a motorhome writing about it, or it may be a feature Dometic no longer provides. It would require an extra wire to to fridge from the +12v pin wired such that it could detect interruption of 12V there. It would probably offer one more way for the fridge to break, though.
Yes, on my B190 motorhome, I had a 12 volt mode that would work only when the engine was running. It was mostly useless; since I was often using the generator anyway to run the rooftop air conditioner, I'd just put the fridge on AC power as well.

I think there may have been something similar years ago for trailers - the trailer would have a 12 volt mode on the fridge, which was powered off the umbilical, probably using the wire that is now just general +12 volts for the trailer. However, that hasn't been used in several decades, and this was a new trailer.
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Old 11-13-2014, 12:17 PM   #12
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We have always left the propane frige on while traveling, when caught in very cold weather the furnace is turned on and again never a problem ...
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Old 11-13-2014, 12:25 PM   #13
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Quote:
Originally Posted by m.hony View Post
You can run the fridge on LP while traveling. It automatically shuts off for 15 minutes or so for fuel stops. I don't know how it knows- maybe when the truck's ignition is shut off the converter knows?
We've been running the fridge on LP while traveling 4 years - food keeps at 36 degrees-
There were some early Dometic 3 way refrigerators which used a sensor wire to the Tow Vehicle or Motorhome ignition switch which turned the refrigerator off for 15 minutes anytime the ignition was cut. They were not very successful and required extra wiring and are no longer made as far as I know.

The refrigerator does not shut off automatically for 15 minutes at fuel stops unless it has this rare feature and it is properly hooked up.
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Old 11-13-2014, 01:39 PM   #14
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In my business, folks always ask how to operate their refer while driving and being safety conscious, I always advise to have the LP turned off while underway... here's why... I have a customer who was in this practice and had a tire crater while he was at highway speed... the shrapnel cut through the floor, plumbing, electrical and yes, LP also... long story short, the unit caught fire and they got pulled over with enough time to get out of the truck. The entire unit burnt to the ground in under five minutes. That said, the unit was on poor quality Asian tires that self destruct a lot anyways. If quality tires are used, this episode probably wouldn't happen... that said, the RV refers of today are, in themselves, completely safe for travel. Would I do it? Absolutely but for all those on cheap tires, take the advise and go with a quality tire and keep them properly inflated. Also, try to use a TPMS if possible.
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