Dometic 3- Way Fridge

[engnrsrule]

I wanted to share some info about our Dometic, original equipment in our 2006 Roadtrek.

The fridge quit working on propane last year and it turned out to need a board. That event brought about some more detailed monitoring of battery consumption, as it just about killed our coach battery to run it on 12v while boondocking.

We got the board replaced and it all works fine. To improve its performance I added auxiliary cooling fans behind the fridge, which really helped - I have a pretty detailed thread covering these mods. That also led to upgrading the coach batteries to two 6v golf cart batteries for a total of 235 Ah and installing a Victron Battery Monitor. Another wise $20 investment is wireless thermometers for the fridge and freezer. These provide an audible alarm if temps get out of range, and let you know all is well without opening the door.

I know some people ride with the fridge running on propane, but I see a lot of states prohibit this, so I choose not to. I have prioritized my fridge operation as follows:

- Use 12v when Rolling under power, or brief travel stops (less than a few hours)

- Use Propane when stopped overnight or for more than a few hours and 110 is not available.

- Use 110v whenever it is available.

I was in a private discussion with another Roadtrekker and wanted to share some of that conversation. The discussion was about how much power is consumed in 12v mode, so I conducted the experiment below. This tends to support my protocol above.

Running only on the coach batteries I set the fridge to 12v. It started at ambient temp of 81 degrees. With that the only thing running it was pulling 11.3 amps. My Victron reported 10 hours remaining battery life.

Then I plugged in 110 and set the fridge on 110 to cool it down. After a couple of hours it was at 38 degrees.

I left the shore tie connected and shifted the fridge to 12v. After a couple of hours the Victron was still at 100%, demonstrating that the charger was keeping up with the draw from the fridge.

I unplugged the shore tie and left the fridge on 12v. A couple of hours later I checked it and it was drawing 11.2 amps. Battery life was showing 10 hours. (It typically shows 240 hours at 100% with nothing running).

Conclusion, 12v should be avoided except when rolling. It is probably OK to leave it on 12v for travel breaks, but if stopped overnight or more than a few hours it would be wise to switch to propane.

I also have not yet experienced any problems with being off level a bit. It seems like if it's level enough to sleep, it works.

[GallenH]

Thanks for the information. Having a 3-way, I agree completely. Just for clarification, when you were on shore power and ran the fridge on 12v, that was just part of the experiment. Normally, if on shore, you would run it in 110v mode, correct?

[k1hog]

Good information.

[engnrsrule]

Gallen,

Yes, that part of the test was only to determine net gain or loss on coach battery. I expected the outcome due to the stepped charging system, just wanted to confirm.

Another aspect of this would be looking down the road a bit. I think if I were to ever move to a compressor fridge (and lose propane) it would actually be a lower draw on 12v, and might be adequately offset by adding some solar. I think 10 hours is too close a margin to hope solar would put back what was used overnight. This is also impacted if we are in a national park or other place that has no shore tie and limits when generators may be run.

[Doneworking]

Your carefully reported results are exactly the same as my experiences over the years with two Roadtreks with three way refrigerators.

I do find that the most effective setting is on gas. I consider 12v to be a maintainer and not a cooling mode.

I would also comment that most RVs and I suspect all trailers do not have the 12 volt third alternative. Running them down the road on propane works fine except you have to remember to turn them off before pulling up to gas up at the service pump.

Finally, I can't imagine NOT having a wireless thermometer in an RV refrig.

[Bud]

"To improve its performance I added auxiliary cooling fans behind the fridge, which really helped ..."

You might consider running on ac, 110v power with the inverter, when it is hot and fridge is not cold enough.

Bud

[engnrsrule]

Originally Posted by Bud

"To improve its performance I added auxiliary cooling fans behind the fridge, which really helped ..."

You might consider running on ac, 110v power with the inverter, when it is hot and fridge is not cold enough.

Bud

Bud, I cannot imagine that being better than straight 12v. Plus it adds the inverter internal load to the drain unless the resistance heating elements associated with 110 are somehow more efficient than the 12v heating elements.

In boondocking mode I will most likely be running it on propane, which is its most effective mode.

[GallenH]

I'm not sure that 110v+inverter is less drain on the batteries. It's probably more. But let's suppose that you're going to use one of these only when driving. My question is whether or not the 110v+inverter cools better than the 12v, which for most is, at best, a "maintainer." I've often wondered this since I've at times seen my fridge gradually creep up when driving in the desert heat and on 12v.

[booster]

Originally Posted by GallenH

I'm not sure that 110v+inverter is less drain on the batteries. It's probably more. But let's suppose that you're going to use one of these only when driving. My question is whether or not the 110v+inverter cools better than the 12v, which for most is, at best, a "maintainer." I've often wondered this since I've at times seen my fridge gradually creep up when driving in the desert heat and on 12v.

In most of the 3 way frigs, the AC heater is larger than the DC heater, in watts. For that reason it would cool better on AC than DC, just as it does when on shore power, if the inverter is large enough and generates waveform that gives full power.


On AC through inverter would take more power as it is a bigger heater and you need to add the inverter losses.

[Bud]

Originally Posted by booster

In most of the 3 way frigs, the AC heater is larger than the DC heater, in watts. For that reason it would cool better on AC than DC, just as it does when on shore power, if the inverter is large enough and generates waveform that gives full power.


On AC through inverter would take more power as it is a bigger heater and you need to add the inverter losses.

Running on ac is no big deal with an 05/04 Roadtrek 190, plenty of alternator amps to power and Charge. Rarely run with propane. If someone can find the Watts ac vs dc with their refer, it will be obvious why dc.............

Bud

[GallenH]

So here's a question. I've got an old PW. Single 27group AGM battery. No inverter. What kind of setup would it take to run 110v on an inverter while driving (only). [Is it even worth it?]

Perhaps better in a new thread? But:

If I add battery capacity (say another 27 AGM) is my alternator sufficient to charge the two?

If I were to add an inverter, how do I calculate the size?

So many questions...........

[Bud]

Originally Posted by GallenH

So here's a question. I've got an old PW. Single 27group AGM battery. No inverter. What kind of setup would it take to run 110v on an inverter while driving (only). [Is it even worth it?]

Perhaps better in a new thread? But:

If I add battery capacity (say another 27 AGM) is my alternator sufficient to charge the two?

If I were to add an inverter, how do I calculate the size?

So many questions...........

I have 2 group 27 marine deep cycle batteries. My 05/04 Roadtrek Van chassis powers the refer and charges the batteries with no problem. I don't recall the watts ac vs dc, but it is More with ac. For years folks like Roadtrek dealers and others would say that dc was only to maintain the cold temperature. Why? It simply did not provide the heat that propane and ac would. So buying groceries at noon and driving off is not going to work out very well, thus ac or propane - noticeable difference vs dc with my dometic. I don't doubt that there may be absorption refers with equal performance ac or dc.

I do recall that the watts on dc was less than 200, so maybe a 300 watt inverter. My original inverter was NOT what Roadtrek claimed, 600 watts. That was the surge, continuous was about 380.

Thanks to avanti, I can simply switch between ac and propane. The ac will be shore power, then generator, then inverter automatically, IF I remember to turn on the inverter.

[SteveJ]

Originally Posted by GallenH

So here's a question. I've got an old PW. Single 27group AGM battery. No inverter. What kind of setup would it take to run 110v on an inverter while driving (only). [Is it even worth it?]

Perhaps better in a new thread? But:

If I add battery capacity (say another 27 AGM) is my alternator sufficient to charge the two?

If I were to add an inverter, how do I calculate the size?

So many questions...........

I use this for an inverter. I've not put a scope on it but it does charge my cordless drill which a MSW inverter did not.

https://smile.amazon.com/gp/product/...?ie=UTF8&psc=1

I do not have it configured to run the fridge, just charging the laptop toothbrushes, razor, and powering a stick vacuum. It's only 300 watts so I just wired it into the converter/charger box.

You would want to verify your fridge specs but my 4 cf Dometic draws 175 on the 110 heater so this inverter would work fine for that.

You will either have to rig up an extension cord to run to the fridge cord or put in some sort of transfer switch for supplying power to current outlet. Do NOT wire the inverter outlet directly to any 110 volt wiring in the coach without a transfer switch of some sort. I'm thinking the transfer switch could be as simple as a 3-way manually operated light switch or a more convenient automatic switch. Edit to add: a pass through style inverter would work and simplify things as it will have a built in transfer function.

[hbn7hj]

It has been several years so I can’t remember the specifics but I replaced the DC heater in the RM2354 3-way fridge with a later higher wattage unit. It helps.

If you look at the latest parts list you can find it. Sorry I can’t be more specific.

I have run an RM2663 unit on AC through an inverter while driving with no problems. The AC heater has a higher wattage rating than the DC heater.

To end the problem I have a replacement compressor cooling unit for the RM2663 that I haven’t installed yet. Such a unit is not available for the class B RM2354. I don’t have the power for it anyhow.

[peteco]

Originally Posted by hbn7hj

It has been several years so I can’t remember the specifics but I replaced the DC heater in the RM2354 3-way fridge with a later higher wattage unit. It helps.

If you look at the latest parts list you can find it. Sorry I can’t be more specific.

I have run an RM2663 unit on AC through an inverter while driving with no problems. The AC heater has a higher wattage rating than the DC heater.

To end the problem I have a replacement compressor cooling unit for the RM2663 that I haven’t installed yet. Such a unit is not available for the class B RM2354. I don’t have the power for it anyhow.

Didn’t realize a higher wattage 12v heater was available for the RM2354. I have a 2554, I wonder if it would work. What is the part number?

I usually use the 12v while driving and it usually holds the temp ok.

[Doneworking]

I sense on this thread and others on the B forum a reluctance on the part of many to use the gas setting on the refrig. I am curious as to why??? It obviously is more efficient than 12v or 120v and is very stingy on lp useage. Is it a concern about the flame itself and having to extinguish it before filling up with fuel or is it just a personal preference?

[hbn7hj]

I prefer LP but I do not use it while moving.
Never 12 volts with the engine off.

The RM2554 already has the 175 watt heater. Mine had 150 watt.
You could use the one from the RM 2663 It draws 18 amps. Probably not recommended ‘cause the AC heater is 175 watts.

Quoted from the service manual:
You should obtain the following readings ± 10%:

Model Watts Volts Ohms
RM2354 150 12 .96
RM2454 175 12 .80
RM2554 175 12 .80
RM2663 215 12 .67

NOTE: The DC mode is a holding mode not a full cooling

[jrobe]

The other option is to just upgrade at some point to a modern, efficient compressor refrigerator and forget about propane, 110v and generators and never have to think about refrigeration anymore. With a decent alternator, we can make a trip to the local store and replace the battery power that the refrigerator uses in a day. I don't even have a solar panel but it wouldn't take a very big one to virtually do the same. My biggest concern is monitoring the controller adjustment so the beer doesn't freeze on 12V power.

[SteveJ]

I'd like to raise a few counterpoints here.

Originally Posted by jrobe

The other option is to just upgrade at some point to a modern, efficient compressor refrigerator and forget about propane, 110v and generators and never have to think about refrigeration anymore.

I agree, as long as we are talking a fridge with a Danfoss style compressor. I haven't seen a dorm fridge with low enough power usage for me to use. I do not want to listen to the genny drone on and on.

With a decent alternator, we can make a trip to the local store and replace the battery power that the refrigerator uses in a day.

One would need lithium batteries and likely a second alternator for this to work. This is a substantial investment if not currently equipped

I don't even have a solar panel but it wouldn't take a very big one to virtually do the same.

The marine fridges with the Danfoss compressor use about 30 to 50 amp hours per day from what I have read. Booster and others have good info on this. I do not as I still have an absorption fridge. A general consensus seems to be adding 100 watts of solar and one more battery(using LA)would handle the marine fridge. A 110 volt dorm fridge would require several hundred more watts of solar and matching battery capacity, depending on it's power consumption.


My biggest concern is monitoring the controller adjustment so the beer doesn't freeze on 12V power.

Agreed.

Background. I use very little power when boondocking. My electrical average use is 12-25 AH/day. A single 100 watt portable solar panel would fully charge my single group 29 battery on a mostly sunny day. I'm now running 150 watts so a partly sunny day now works. My assumptions if I have to replace my fridge(I would go marine) are that I will have to get another battery, increase the solar to 200 watts and I will be able to only go two cloudy days on the batteries versus my current ability of going three days without solar.

[booster]

Originally Posted by SteveJ

I'd like to raise a few counterpoints here.

Quote:
Originally Posted by jrobe
The other option is to just upgrade at some point to a modern, efficient compressor refrigerator and forget about propane, 110v and generators and never have to think about refrigeration anymore.

I agree, as long as we are talking a fridge with a Danfoss style compressor. I haven't seen a dorm fridge with low enough power usage for me to use. I do not want to listen to the genny drone on and on.

With a decent alternator, we can make a trip to the local store and replace the battery power that the refrigerator uses in a day.

One would need lithium batteries and likely a second alternator for this to work. This is a substantial investment if not currently equipped

I don't even have a solar panel but it wouldn't take a very big one to virtually do the same.

The marine fridges with the Danfoss compressor use about 30 to 50 amp hours per day from what I have read. Booster and others have good info on this. I do not as I still have an absorption fridge. A general consensus seems to be adding 100 watts of solar and one more battery(using LA)would handle the marine fridge. A 110 volt dorm fridge would require several hundred more watts of solar and matching battery capacity, depending on it's power consumption.


My biggest concern is monitoring the controller adjustment so the beer doesn't freeze on 12V power.

Agreed.





Background. I use very little power when boondocking. My electrical average use is 12-25 AH/day. A single 100 watt portable solar panel would fully charge my single group 29 battery on a mostly sunny day. I'm now running 150 watts so a partly sunny day now works. My assumptions if I have to replace my fridge(I would go marine) are that I will have to get another battery, increase the solar to 200 watts and I will be able to only go two cloudy days on the batteries versus my current ability of going three days without solar.

I would agree with almost all of the above, and would have been with all of it until the recent threads about the 110v dorm frigs. The new energy star rated units look to be very efficient and in the same range as many of the marine units. What we don't know is what conditions they are designed to function in, both from and bouncing and vibration standpoint and from ambient conditions standpoint. Many/most 110v house frigs are designed to specs that include a quite narrow range of ambient conditions like you would see in occupied areas and we see much wider ranges in our vans, especially if you are externally vented. Our compressor frig condenser section has seen 20*F to 105*F conditions and handled it fine, just using more energy when hotter. We don't yet know if the new dorm frigs would do as well yet, as we haven't seen any real testing yet. Increasing cooling efficiencies usually come at a cost, and operating range may be one of them in this case.