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-   -   Dometic refrigerator 12vDC operation (http://www.airforums.com/forums/f425/dometic-refrigerator-12vdc-operation-13409.html)

walter1 08-20-2004 02:14 PM

Dometic refrigerator 12vDC operation
 
I have a 2003 Dometic RV refrigerator model RM2551 which is two way LP/120vAC. Is it possible to convert it to model RM2554 which is same basic unit except 3 way LP/120vAC and 12vDC so it can run while driving on vehicle 12vDC? It appears it requires the 12vDC heating element, wiring to circuit board and perhaps a switch. Anyone done this? Where can I obtain 12v heater element?

Thank you, Walter

Pahaska 08-20-2004 02:45 PM

Should be possible
 
I have been thinking of the same thing. The difference is that on the boiler, there are two metal tubes instead of one. One tube for the AV heater and one tube for the DC heater. I would think a second tube of appropriate size coule be clamped tight to the boiler, the DC heating element inserted, and a heavy wite run to a heavy duty switch which would be wired to the battery with appropriate size wire. The switch could be anywhere and completely independent of the refrigerator controls; the DC element will never overcool the refrigerator. Thermal grease could be used to get good heat transfer.

Just make sure to turn it off when the unit is in operation. Also, you wouldn't have the low-voltage battery protection of the standard refrigerator controls.

You should find the wattage and part number for the DC heater in the manual (there is usually a single manual for the 2-ways and 3-ways with electrical diagrams for each). The Dometic site also should have the info. With the part number or wattage in hand, order the heater from Camping World or any RV supply.

nickcrowhurst 08-21-2004 10:39 AM

Walter, I have the 3-way Dometic, but I don't find the 12 volt system much use. If I remember correctly, the current draw is about 22 amps. It takes a high-grade wiring system to get that much current from a tow vehicle alternator and pass it through 30 feet of wiring and the 12 volt heater element in the refrigerator. My Dodge Ram 3/4 ton will not keep up with the demand. When travelling, some are happy to use the LP gas system (turn it off before entering a gas station), and others find that the contents stay frozen all day without any cooling. You can always pack a load of ice in the refrigerator, or turn it to its coldest for a few hours before travelling. In short, for my purposes the 12 volt system does not justify its complexity or expense. Nick.

JohnG 08-21-2004 11:01 AM

I found out by replaceing an altenator onmy tow vehicle a few years back that the 12 volt system is really not worth it.

I understand your concern of driving with the LP on, but that isn't as bad as you might think.

If you insist on traveling with cold stuff and don't want to use the LP then you might consider using an ice chest. Or you could just buy the stuff you need at a nearby store after you get your camp set up.

overlander64 08-21-2004 11:20 AM

Dometic refrigerator 12vDC operation
 
I have always had the Dometic 3-Way refrigerators in my Brand X coaches and have never had a problem operating on 12-volt - - and this is since my first coach that was equipped in this manner in 1980. I have never traveled with the refrigerator set to LP, and turning off the LP valves is on my checklist of pre-travel tasks. The dealer who wires my tow vehicle has always known in advance of the refrigerator system and has wired accordingly. On my older tow vehicles, I utilized heavy duty alternators with adjustable regulators - - but have made no particular modifications to either my '99 Suburban nor its '95 Chevrolet predecessor. In fact, since having the new Dometic 3-way refrigerator in my '64 Overlander (installed in 1999), the LP mode has only been used long enough to be sure that it functioned properly. A key hint in having the system function properly is to pre-cool the unit using the 120-volt element (or LP if you prefer), then switch to the 12-volt. There is no question in my mind that when the original Dometic 2-way refirgerator in my Minuet fails that it will be replaced with a new 3way Dometic.

Good luck with your investigation!

Kevin

walter1 08-21-2004 06:30 PM

Thanks for the input. It still sounds like a good idea if it works well but I don't want to be buying alternators. I plan to do a lot of boondocking away from city power source. I’m just very unsure about towing on dirt forest roads and long highway stretches with LP flame going. That could be worse than no refer, no more trailer. I can use LP while camping and cool it down good before travel. I found the schematic for wiring but no part numbers. Wiring and switch are easy, I need heater element number and install info. Dometic offers only “You can’t legally do that”.

New Idea:
Can I run it on AC inverter power while driving and charge battery through tow vehicle?
Thank, Walter

gecko 08-25-2013 11:03 AM

Dometic 12v operation off battery bank/solar while towing?
 
Our experience with our Dometic RM 3762 in our 2009 International is that it does not keep cool enough on propane in 90plus temperatures that we often encounter in the West. It does a much better job on AC--it cools down more quickly, and holds temperatures during the hot days better.

While traveling, running on propane on hot days is inadequate to keep contents at safe temperatures, and the reefer often turns off from wind blowing out the propane fueled flame, making the situation worse.

We have upgraded our Airstream provided solar system to 4 Lifeline AGM six volt batteries yielding a 440 amp battery bank for boon docking, and have 260 on the roof instead of the stock 112. We have the Airstream-installed 600 watt inverter, and there is already an outlet from the inverter in the reefer cabinet for access for another small-draw appliance.

(1) Will the 600 watt inverter safely handle the load from the Dometic RM 3762, both at startup and continuously if we plug the Dometic into the inverter outlet?
(2) Is there any way to isolate the load on our 2012 one-ton Sprinter's alternator so that the battery bank is still being charged by solar when towing?

Thanks!

Aage 08-25-2013 11:27 AM

gecko: fans can make a dramatic difference.

There are three possible places to put them, up to you to decide which one might give you what you need.
  • Under the top cooling unit fins (back of refer) will dramatically increase cooling effect at fins.
  • at the opening to the roof vent will dramatically improve air circulation behind the refer (remove hot air from cabinet)
  • on the fins inside the refer. there are kits sold that make this a neat-looking and effective solution to extra cooling, simply by moving the air around inside the refer. Great if your family likes to "window shop" in your refer. ;)

I would recommend installing switches so that any or all fans may be turned on or off. Those little "muffin" fans (commonly used in computers, can be bought cheaply at computer recyclers) do tend to be quiet, but it might be a Good Thing to be able to silence some or all at night...

The fans are low power consumers, BTW. All the ones I bought (four for $20) draw only 0.15A each.

Also, investigate the cavity behind your refer with an eye to increasing the flow over the top cooling unit fins. In some installations a big difference can be made by just using some home-made baffling.

I am about to try the "inside refer" fan plus the "in the roof vent" fans. If my family ever leaves me some time for doing this, I promise to report back. :D

Aage

graysailor 08-25-2013 11:43 AM

Can you provide any more info on the inside the refer kits for moving air around? I have used something similar on my boat but they were battery operated.

Aage 08-25-2013 03:28 PM

Quote:

Originally Posted by graysailor (Post 1345476)
Can you provide any more info on the inside the refer kits for moving air around? I have used something similar on my boat but they were battery operated.

Have a look here. He provides at least two different models, one marginally more expensive than the other, why I do not know.

The good part is that if your refer has an interior light, getting power is really simple (mine doesn't :( ) At the worst though, every fairly modern refer needs 12VDC for its "brains" (PC board), so power is rarely far away. The fan set itself merely pushes onto the fins of the cooler. Brilliant!

gecko 08-26-2013 11:31 AM

12 volt dc thru inverter
 
Thanks for the fan/baffle tips.

Since you indicate that you are thinking about trying these, this has been our experience in the past with these suggestions:

Interior fan: We tried an excellent battery operated model at our dealer's suggestion. But the limiting factor was placement of stuff inside the refrigerator to allow circulation more than an actual fan to force circulate air. Once we rearranged stuff, the refrigerator was better able to handle the load, and the fan seemed to make little difference other than taking up more room. But at the start of a long trip, we do have a lot of stuff to fit into the reefer! The fan attached to the fins sounds VERY cool, though :-)

Chimney fan: This was another suggestion from our Airstream dealer. Because we're in SoCal, a lot of folks are taking their Airstreams into the desert where temperatures over 100 are common. Beautifully mounted with a very tasteful shut off switch (not only for quiet, but also to further reduce amp draw when dry camping), this device did--absolutely nothing to help!

Coil fan/Baffles: Haven't tried this one. But ironically, if one where to put air baffles on the air vents for this compartment (to keep the propane light from blowing out while towing), it would actually reduce air flow over the coils, too. Theoretically possible to build a separate baffle box around the flame area, and then a separate fan to blow on the coils.

But with the lack of success of the first two perfectly logical solutions above, I'd kinda like to cut to the chase and get this thing solved. In every case, no matter how the inside of the reefer is packed, running the reefer on AC has always yielded much faster initial cooldown, much lower ambient temperatures, and shouldn't blow out while going down the road.

So back to the original question--(a) will the Airstream installed 600 watt inverter that's already in our coach handle the initial and sustained load of our Dometic running in AC mode and (b) to avoid any alternator overload while towing, is there any safe way to keep the trailer lights/electric brakes hooked to the truck but still isolate the trailer battery bank/inverter system from the truck's alternator, leaving the battery bank to depend on solar only?

This combo would inexpensively allow us to run the reefer on AC while towing without damaging the Sprinter's alternator, with all the benefits to the reefer system. We typicallly plug in to shore AC in the evening while traveling, so the batteries would top off at night if the solar didn't keep up during the day.

Thanks everybody!

daveswenson 08-26-2013 12:11 PM

I just ordered the Deluxe one that fits on the fins. I'll check back in when I've had a chance to install and test it.

Jammer 08-26-2013 04:06 PM

Quote:

Originally Posted by gecko (Post 1345448)
Our experience with our Dometic RM 3762 in our 2009 International is that it does not keep cool enough on propane in 90plus temperatures that we often encounter in the West. It does a much better job on AC--it cools down more quickly, and holds temperatures during the hot days better.

While traveling, running on propane on hot days is inadequate to keep contents at safe temperatures, and the reefer often turns off from wind blowing out the propane fueled flame, making the situation worse.

Why not fix the propane system? You probably have a clogged orifice, a defective or misadjusted gas valve, or perhaps the tank regulator isn't providing propane at the proper pressure.

Quote:

We have upgraded our Airstream provided solar system to 4 Lifeline AGM six volt batteries yielding a 440 amp battery bank for boon docking, and have 260 on the roof instead of the stock 112. We have the Airstream-installed 600 watt inverter, and there is already an outlet from the inverter in the reefer cabinet for access for another small-draw appliance.

(1) Will the 600 watt inverter safely handle the load from the Dometic RM 3762, both at startup and continuously if we plug the Dometic into the inverter outlet?
Yep.

Quote:

(2) Is there any way to isolate the load on our 2012 one-ton Sprinter's alternator so that the battery bank is still being charged by solar when towing?
Not sure what you're trying to accomplish. Usually the path is high-resistance enough that the alternator won't do much anyway. If you don't want it to charge the batteries at all, just disconnect the charge line somewhere.

Pahaska 08-26-2013 04:49 PM

Quote:

Originally Posted by gecko (Post 1345448)
Our experience with our Dometic RM 3762 in our 2009 International is that it does not keep cool enough on propane in 90plus temperatures that we often encounter in the West. It does a much better job on AC--it cools down more quickly, and holds temperatures during the hot days better.

Then you have a propane system problem. The propane puts more BTUs in the system than does the AC heating element. The box should cool more quickly and stay cool better on propane.

A post above mentions some things to check. In my case, it was the regulator set too low that caused poor cooling on propane. Once I had the proper propane pressure, the box cools great in even the hottest weather.

gecko 08-27-2013 05:55 PM

Thanks, guys. All very helpful thinking. Duh--hadn't thought to just check thoroughly the propane system, and I'll have the guys do that when we get back.

To answer Jammer's question, what we're trying to accomplish is:

(a) Better cooling by using AC (from inverter) instead of propane. Our experience has been that shore power has provided much better cooling than propane. If your instinct about the propane system being fouled or the regulator iffy is correct, then that may fix that single important issue. Again, thanks!

(b) Better and foolproof cooling while towing by using AC from inverter. Again, if propane system is the problem, then we can just deal with creating wind baffles, but if the AC/inverter is a good solution, we won't have to deal with that issue.

(c) While doing (b), making sure that we don't damage the alternator with a heavy load of supplying the reefer through the battery bank/inverter. I've read on other strings that there have been alternator problems when towing due to running off batteries and the associated tasking of the alternator.

(d) Saving battery life (four xpensive Lifeline AGM six volt 220 amps units wired to provide 12v 440 amp system) by keeping them off the Airstream- provided single level charge converter. A reputable tech just informed us that although we correctly replaced our converter in our factory solar system from the Airstream supplied single level charger to a three level charger, the primary converter for our coaches are also only single level. If we can run the reefer on inverter supplied AC, we can avoid using shore power, at least during the day, and therefore avoid 24 hour flood charging of the battery bank. We'd simply turn off the shore power in the morning and let the reefer run off the battery bank/solar/inverter all day, and then re-engage the shore power if we want to run the HVAC at night. This instead of replacing another lesser quality Airstream factory part with expensive after-market labor (the primary charge converter.)

We're hoping that a very simple solution for ALL of the above will be to unplug the reefer from its shore power supplied AC socket and plug it in to the inverter supplied AC socket that we installed to power another very small draw appliance that's installed above the reefer, so there's already an inverter supplied AC socket installed in the reefer cabinet with easy access.

Since you guys are confident that the rather weak 600 watt inverter supplied by Airstream with the factory package is adequate to the task, the only remaining problem seems to be possible overload on the alternator when towing.

Any more thoughts?

Jammer 08-28-2013 10:51 AM

Quote:

Originally Posted by gecko (Post 1346560)
Thanks, guys. All very helpful thinking. Duh--hadn't thought to just check thoroughly the propane system, and I'll have the guys do that when we get back.

To answer Jammer's question, what we're trying to accomplish is:

(a) Better cooling by using AC (from inverter) instead of propane. Our experience has been that shore power has provided much better cooling than propane. If your instinct about the propane system being fouled or the regulator iffy is correct, then that may fix that single important issue. Again, thanks!

(b) Better and foolproof cooling while towing by using AC from inverter. Again, if propane system is the problem, then we can just deal with creating wind baffles, but if the AC/inverter is a good solution, we won't have to deal with that issue.

Right, we've covered this.

Quote:

(c) While doing (b), making sure that we don't damage the alternator with a heavy load of supplying the reefer through the battery bank/inverter. I've read on other strings that there have been alternator problems when towing due to running off batteries and the associated tasking of the alternator.
You're not going to damage the alternator in the tow vehicle by virtue of the presence of a heavy load in the trailer, unless the alternator is marginal due to dirt, age, or small size. If any of that applies, you should replace it anyway. The charge circuit from the tow vehicle to the trailer just won't deliver the kind of current that would pose a problem for the alternator, and on most vehicles, it's fused at 30a or less.


Quote:

(d) Saving battery life (four xpensive Lifeline AGM six volt 220 amps units wired to provide 12v 440 amp system) by keeping them off the Airstream- provided single level charge converter. A reputable tech just informed us that although we correctly replaced our converter in our factory solar system from the Airstream supplied single level charger to a three level charger, the primary converter for our coaches are also only single level. If we can run the reefer on inverter supplied AC, we can avoid using shore power, at least during the day, and therefore avoid 24 hour flood charging of the battery bank. We'd simply turn off the shore power in the morning and let the reefer run off the battery bank/solar/inverter all day, and then re-engage the shore power if we want to run the HVAC at night. This instead of replacing another lesser quality Airstream factory part with expensive after-market labor (the primary charge converter.)
Sorry, but this is inside-out thinking. Batteries deteriorate with use. If you're constantly charging and discharging the batteries, they'll deteriorate faster. Also, the stock converter will probably not fully charge your batteries overnight, at least not in cool weather. If you are going to run AGMs you need a new converter.

New converters are way cheaper than 4 new lifeline AGMs, which is what you'll need to buy in a couple years if you don't replace the converter.

I run flooded batteries in my rig. They're cheaper and they're less prone to damage from overcharging. AGMs have their advantages but if you're going to play the AGM game you've got to have a converter that can handle them. I would suggest the Xantrex TrueCharge with the temperature compensation probe, but there are other good ones out there.

Quote:

We're hoping that a very simple solution for ALL of the above will be to unplug the reefer from its shore power supplied AC socket and plug it in to the inverter supplied AC socket that we installed to power another very small draw appliance that's installed above the reefer, so there's already an inverter supplied AC socket installed in the reefer cabinet with easy access.

Since you guys are confident that the rather weak 600 watt inverter supplied by Airstream with the factory package is adequate to the task, the only remaining problem seems to be possible overload on the alternator when towing.

Any more thoughts?
Sure, one more piece of math. Your refrigerator draws maybe 200 watts. The inverter will draw around 18 amps when the fridge is on. So after less than 24 hours of fridge on-time you'll have a dead battery bank. Maybe less since your converter doesn't charge them fully.

DKB_SATX 08-28-2013 11:34 AM

An excellent 3-stage converter (Iota or Progressive Dynamics 80-amp, e.g.) costs about half of what *ONE* of those big Lifeline AGMs cost. Thinking of a quality converter as "too expensive" when you're managing $1600 worth of batteries is a good definition of false economy.

WALLY 54 08-28-2013 02:52 PM

If it works on either electric or gas, it WILL work on the other. Really, what everybody is saying - to check the propane system - should be your first step. You should check the pressure leaving the regulator to be about 11" of water column pressure and you should have about 7" at the burner. You should check and possibly clean your burner nozzle because it can become gummed up. Soaking it in some alcohol for a day then blowing it out should clear out any obstructions or gook. NEVER stick anything into the nozzle and that is sure to enlarge the hole and will cause excessive heat input to result which could destroy your cooling unit.

The burner itself should be blown out also. If a spider builds a little web inside, that is enough to impact gas flow to the boiler (happened to my water heater). Just a puff or two of compressed air is all you need.

You should also vacuum out/blow out the boiler tube - where the flame goes. If it becomes obstructed with anything like rust particles it could alter how heat flows through the tube.

All of these steps are simple things you should do every year anyway (except cleaning the burner nozzle) to ensure that all the heat gets to the place where it belongs.

graysailor 08-28-2013 11:22 PM

I upgraded my rig with 4 AGM's and getting a quality 3 stage charger is a must. Not that expensive to upgrade your existing Airstream charger. I also added a solar panel for a total of 300W of solar. You will need at least that much with 4 AGM's. Not a good idea to use solar only for charging when shore power is available. Batteries only have so many cycles in them. Use the solars when boon docking.

gecko 08-28-2013 11:47 PM

Thanks everybody for your input. to answer the three inputs:

We have 260 watts of solar. At that time, we were stuck with our limited roof real estate already having the low output 56 watt Airstream supplied panels, and the large output panels that we could find 4 years ago (tons more available now) were 80's. Coupled with a BlueSky converter, however, this system has proved to be quite good for our dry camping uses, which are typically not longer than two weeks--even with some cloudy days and fog limiting input. If we have trouble with the existing panels, we'll definitely swap all four out for 100's or 120's, and have an even more powerful system.

As far as a good converter, it's definitely on our list. But because I'm not comfortable with doing electric myself, it's not only the cost of the converter but the high cost of local labor ($100/hr plus) to install, combined with making it a bigger job than just swapping out because the local tech feels that the Airstream provided wires are too light, too. I will get a second quote once we return to home base, and it is on the list. It just never would have occurred to me that Airstream would have "cheaped out" on something so important.

The advice about the batteries having only so many cycles so do not rely on solar/batteries when shore power is available is excellent. So the replacement of the Airstream converter has moved up the list.

And Wally 54's amplification of the advice (with much appreciated added detail) to check out the propane system is good, too. This is definitely something we will do soon. Of course, the system does currently operate in both modes--it's just that it's much less powerful in propane mode than in electric. All of the advice and experience from you guys has been very helpful in letting us know that this is not normal, and we will focus on this in five weeks once we reach home port (until then, we're on shore power except for the 1500 mile trip home).

Thanks again!


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