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Old 01-31-2012, 11:08 PM   #1
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Converter/Inverter Question

I would like to be able to run our frig while traveling without using the lp gas. I currently have only the converter. What do I need to make this happen?

My trailer is the 07 25' FB.
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Old 01-31-2012, 11:44 PM   #2
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Hello Gaylejoe...

Whats the reason for not running on LP gas? You could come up with an inverter arrangement but im not sure what the advantage is. The burner unit uses very little propane and will switch back to AC when shore power is supplied.

Curious..

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Old 02-01-2012, 12:11 AM   #3
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The 120 volt part of your refrigerator will take about 300 watts max to run the electric heater. To get that amount of 12 volt power from your charge line to the trailer batteries is very difficult as it is about 25 amps. The long run, voltage drop through all the wiring and connections increase the resistance to the point a charge current that high is improbable. I can sometimes get a 10 to 12 amp charge, but more commonly I have only measured 6 to 8 amps.

You could, I suppose, have the inverter in the tow vehicle, wired directly to the battery and then run 120 volts back to the trailer through a new connection system.

But why? The trailer refrigerator will run just fine on propane. I know some feel it is a safety issue and I am on the side of "not a problem". Overall thousands of rigs are on the road every day with propane refrigerators running, and they don't burn up, have explosions, or any real problems. Yes, it can happen, and has happened, but it is exceptionally rare.

I hope this does not start a propane while traveling on vs. off war. We all have our views, and a rehash will not change many minds.
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Old 02-01-2012, 06:25 AM   #4
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IIRC, the conversion from DC to AC,and the boosting of the voltage, means it will take ten times the amperage in DC to make the same amount of AC. If the heating element in the fridge uses 3 amps, it will take about 30 amps of DC to make it. It would be a real strain on your truck's electrical system to do this, along with some pretty heavy wiring to the inverter.
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Old 02-01-2012, 06:49 AM   #5
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Quote:
Originally Posted by gaylejoe View Post
I would like to be able to run our frig while traveling without using the lp gas. I currently have only the converter. What do I need to make this happen?

My trailer is the 07 25' FB.
A 600 watt solar array with a 45 amp solar charger tied into a 600 amp/hour battery bank (4-Lifeline GPL-6CT batteries) and a 2000 watt inverter will do the job. Is it worth about $10,000 installed just to avoid using your RV fridge on LP ?
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Old 02-01-2012, 10:15 AM   #6
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Why Defeat a Time-Proven Design?

Quote:
Originally Posted by gaylejoe View Post
I would like to be able to run our frig while traveling without using the lp gas. I currently have only the converter. What do I need to make this happen?

My trailer is the 07 25' FB.
Your beautiful Airstream is designed and equipped to run on propane. Why the focus on changing something that really doesn't need changing?
Is there more to the story?
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Old 02-01-2012, 11:22 AM   #7
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Quote:
Originally Posted by gaylejoe View Post
I would like to be able to run our frig while traveling without using the lp gas. I currently have only the converter. What do I need to make this happen?

My trailer is the 07 25' FB.
Hi Gayle & Joe.

This question comes up several times a year. There are three sides to the answer.

== Side One. ==

To proceed as you are planning you will need an inverter that can produce 300 watts, continuous, and one Group 27 or Group 31 battery for every two hours you plan to run the fridge off the battery. Since most inverters sold for the RV and consumer market will not deliver anything close to their advertised output continuously you should be looking at inverters rated at around 800 watts.

Your stock converter can be left in place but the batteries will require an overnight charge to come back up to something approaching full charge. If you want them to charge faster, perhaps because you're charging from a generator, you can either get a converter upgrade as well, or an inverter-charger instead of the two separate components. The inverter-charger way of doing things would probably be more expensive because you would end up getting a larger inverter than you would need.

Though the question is often asked, I'm not aware of anyone who has proceeded with such a conversion.

== Side two. ==

If you really want to run the fridge off batteries you're probably better off removing it and replacing it with a marine-style fridge that has one of the 12v Danfoss compressors instead of the absorption system. The current draw of these fridges is around 10-20% of that of the 2-way gas/electric fridges, and they're highly regarded as far as reliability and noise levels, and they keep the food cold, and so on.

Then you won't need an inverter, you probably won't need to upgrade your battery system as much, and if you're planning on a solar or generator setup that can be smaller as well. As a result the costs may prove to be comparable, or lower, than the inverter approach with the existing fridge.

The only disadvantage of the Danfoss fridges is that they won't run on LP.

There are a number of new RVs being sold that take this approach, most of them smaller RVs or ones that are designed without a propane system. I think over on one of the truck camper forums there's someone who has done this conversion to an existing rig, combined with solar panels.

== Side three. ==

Most experienced RVers drive with the propane on. In practice most RV fires are electrical in origin with arson, candles, and cooking fires also contributing to the statistics. I have not seen any reports of actual fires that occurred while moving where the propane system was the source of the fire or contributed significantly to it before the RV was fully engulfed. There are a fair number of reports of propane cylinders coming loose while driving and being dragged down the road, but the design of the tank valves is such that, as frightening as these episodes are, they don't result in fires.
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Old 02-01-2012, 08:27 PM   #8
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I was just wondering if there was another way to run the frig while towing. We do use it on propane but a recent safety class instructor stated anyone doing that is an accident waiting to happen. I was just looking for an alternative method. I appreciate all the comments.
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Old 02-01-2012, 08:54 PM   #9
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Your safety class instructor, though well meaning, should have done his research before making a statement like this. I'm sorry that he created this doubt and confusion.
We have a "safety instructor" here in Albuquerque who is a cornucopia of misinformation on a variety of topics including First Aid. My wife, an ER Nurse, Coronary Care Nurse, and EMT Instructor (all in her previous life) just shakes her head.
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Old 02-01-2012, 09:49 PM   #10
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you'll be fine on propane

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Originally Posted by gaylejoe View Post
I was just wondering if there was another way to run the frig while towing. We do use it on propane but a recent safety class instructor stated anyone doing that is an accident waiting to happen. I was just looking for an alternative method. I appreciate all the comments.
It's good to think about safety. If you want to be extra careful, you should focus on shutting off the refrigerator just before you pull up to a gas pump. As far as I know, that is the only place during normal transportation that the flame from the propane could be a safety risk. I've never heard of any refrigerator accident that involved anything other than a gas station mishap.

I personally no longer even shut off the unit when refueling. Instead, I always refuel at the first pump I get to, and don't pull to the far pump which might allow the open propane flame to be closer to the fuel pump behind me and more or less even with the refrigerator access vent door. By doing this, the propane flame is about 20 feet from possible fuel vapors, more than safe enough.
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Old 02-02-2012, 12:24 PM   #11
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I was just wondering if there was another way to run the frig while towing. We do use it on propane but a recent safety class instructor stated anyone doing that is an accident waiting to happen. I was just looking for an alternative method. I appreciate all the comments.
The RV industry is slow to change but I think that, over the next 10-20 years, we'll see a move away from propane fridges in favor of 12V Danfoss-type setups.

People who assert that there is a safety problem with driving with the propane on usually do so based primarily on the idea that it poses a fire risk in the event of a collision. While such fires are, in the abstract, possible, they are rare compared to fires resulting from the fuel system in the tow vehicle. Your trailer is new enough that it has a number of safety systems to prevent such fires, among them the excess flow check in each of the cylinder valves (which closes and locks in the event of a gas line rupture), and the design of the Acme threaded connection which causes the valve to close if the hose is forcibly removed from the tank. Since nearly all of the propane system is external to the trailer or in well ventilated compartments, the likelihood of gas accumulating in sufficient quantity to create a hazard is rare.

A few months ago I went through the petroleum industry's statistics on refueling fires. Such fires are remarkably rare and are nearly all caused by static electricity. In 10 years of accident reports there were no reports of refueling fires ignited by gas appliances or electric components in the vehicle or trailer.
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Old 02-02-2012, 12:49 PM   #12
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I agree with all comments above but if you continue to worry about this you could install a 3 way fridge. It will use 120/LP/12v DC. I currently have one and like the feature. We just switch to 12v before we hit the road and no worries. When we park or stop for any length of time I will switch back to 120 or LP but using the 12v does save LP and the charge line seems to keep the batteries topped off any way. I think the max current pulled in DC mode is 7 amps so the charge line should be able to keep up with this. Last I checked the cost was around $1800.

ymmv
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