Running a Dometic fridge on 12V

[bwatters60]

I replaced the Dometic RM2554 3-way fridge in my '08 RT 210P with a Nova Kool R5810 (AC/DC model with Danfross compressor) last summer. We've never run short on battery, but we generally don't stay in one spot more than one night when boondocking. So while I had the RT parked for a few days (without staying in it), I decided to test my batteries. I charged the batteries then started and ran the fridge for 12 hours, rested the batteries for one hour, then restarted and ran the fridge for another 12 hours. In summary, I was pleasantly surprised at how well the batteries (2-6V Duracell 235AH) performed and more or less confirmed my calculations that we'll have ample power for our 12VDC electric blankets.

[ProseMan]

kivelaki,

One common problem with those Hymer and Roadtrek fridges: They are very sensitive to voltage at the 12v mark. I was having similar problems with mine in my Roadtrek when the company suggested that the dealer remove the fuse from the 12v line. Apparently the fuse is poorly wired and on my fridge was barely holding together. Once removed, my fridge has been completely reliable when switching from 110v to 12v. I also like the idea of turning off the 110 breaker so the fridge stays on 12v.

[peteco]

Originally Posted by bwatters60

I replaced the Dometic RM2554 3-way fridge in my '08 RT 210P with a Nova Kool R5810 (AC/DC model with Danfross compressor) last summer. We've never run short on battery, but we generally don't stay in one spot more than one night when boondocking. So while I had the RT parked for a few days (without staying in it), I decided to test my batteries. I charged the batteries then started and ran the fridge for 12 hours, rested the batteries for one hour, then restarted and ran the fridge for another 12 hours. In summary, I was pleasantly surprised at how well the batteries (2-6V Duracell 235AH) performed and more or less confirmed my calculations that we'll have ample power for our 12VDC electric blankets.

Do you find the freezer temp to be an issue as they are in the teens (13-17 deg)? Does your food, and ice cream in particular, stay sufficiently frozen hard solid?

My RM 2554 holds freezer temp to around 0 degrees, thus everything stays hard frozen. THe fridge is usually under 34-39 deg, though very hot weather can push it a little above 40-deg. But Saturday the fridge went up to 44 deg (in 99 degree weather), but the freezer held below about 7 degrees. I could have helped the fridge by moving some ice packs into the fridge.

[bwatters60]

Originally Posted by peteco

Do you find the freezer temp to be an issue as they are in the teens (13-17 deg)? Does your food, and ice cream in particular, stay sufficiently frozen hard solid?

My RM 2554 holds freezer temp to around 0 degrees, thus everything stays hard frozen. THe fridge is usually under 34-39 deg, though very hot weather can push it a little above 40-deg. But Saturday the fridge went up to 44 deg (in 99 degree weather), but the freezer held below about 7 degrees. I could have helped the fridge by moving some ice packs into the fridge.

Our experience with the 2554 was similar to yours, and my wife works in food service so it wasn't acceptable to her. And the freezer temps in the Nova Kool were also not up to her expectations. So I exchanged a couple emails with Nova Kool support about our less than desirable freezer temps – their responses are below.
Response #1 - One thing you could try is to "slow" the cold air drop from the back of the freezer portion of your 5810. You can pick up some pink 1 inch insulation foam from Home Depot or other hardware stores and you can try and fill the gap between the back of your freezer and your freezer cold plate. I also want to confirm that you have the plastic drip tray installed right now? This will help keep some of the freezer cooling in also.
Response #2 - Its probably best to experiment a little bit at a time, starting with the back of the cabinet. You can go ahead and plug the entire gap at the back because the cold air from the freezer should still pool on your drip tray and then spill over into the refrigerator keeping it cool. You can always plug the entire back of the freezer compartment and see how it affects the refrigerator temperatures then cut it back a little bit if need be.
I used some 5/8” pink foam insulation board to fill the opening between the rear of the freezer (sides and bottom only) and the refrigerator. I also packed dish foam or foam wrap (very thin) between the inner and outer walls of the sides of the freezer box. Initially I also placed bubble wrap (about ¾” thick) in the drip tray but found that this resulted in unacceptable temperatures in the fridge. After a day or so of experimenting we set out on our 1300 mile return trip to Texas and traveled thru a couple days of hot days including temperatures exceeding 100. The refrigerator ranged from 35-39 degrees while the freezer ranged from 11 to 0 degrees. During the hottest part of the trip the freezer was typically about 2 to 5 degrees. So our freezer full of gluten free pasties from the Iron Town Pasty shop arrived in TX safe and soundly frozen. We’re very happy with performance of our Nova Kool with these slight modifications. Oh, the fridge setting ranged from about 5.5 to 6 (out of 7).

[peteco]

Originally Posted by bwatters60

Our experience with the 2554 was similar to yours, and my wife works in food service so it wasn't acceptable to her. And the freezer temps in the Nova Kool were also not up to her expectations. So I exchanged a couple emails with Nova Kool support about our less than desirable freezer temps – their responses are below.
Response #1 - One thing you could try is to "slow" the cold air drop from the back of the freezer portion of your 5810. You can pick up some pink 1 inch insulation foam from Home Depot or other hardware stores and you can try and fill the gap between the back of your freezer and your freezer cold plate. I also want to confirm that you have the plastic drip tray installed right now? This will help keep some of the freezer cooling in also.
Response #2 - Its probably best to experiment a little bit at a time, starting with the back of the cabinet. You can go ahead and plug the entire gap at the back because the cold air from the freezer should still pool on your drip tray and then spill over into the refrigerator keeping it cool. You can always plug the entire back of the freezer compartment and see how it affects the refrigerator temperatures then cut it back a little bit if need be.
I used some 5/8” pink foam insulation board to fill the opening between the rear of the freezer (sides and bottom only) and the refrigerator. I also packed dish foam or foam wrap (very thin) between the inner and outer walls of the sides of the freezer box. Initially I also placed bubble wrap (about ¾” thick) in the drip tray but found that this resulted in unacceptable temperatures in the fridge. After a day or so of experimenting we set out on our 1300 mile return trip to Texas and traveled thru a couple days of hot days including temperatures exceeding 100. The refrigerator ranged from 35-39 degrees while the freezer ranged from 11 to 0 degrees. During the hottest part of the trip the freezer was typically about 2 to 5 degrees. So our freezer full of gluten free pasties from the Iron Town Pasty shop arrived in TX safe and soundly frozen. We’re very happy with performance of our Nova Kool with these slight modifications. Oh, the fridge setting ranged from about 5.5 to 6 (out of 7).

I am pleasantly surprised Nova Kool was responsive to your issues. But I wonder why they have not made the recommended mods a permanent part of the refrigerator. Do they compromise something else? Is it because most users are OK with higher freezer temps???

[bwatters60]

Originally Posted by peteco

I am pleasantly surprised Nova Kool was responsive to your issues. But I wonder why they have not made the recommended mods a permanent part of the refrigerator. Do they compromise something else? Is it because most users are OK with higher freezer temps???

I wonder the same. I thought of blocking off the open area in the back of the freezer but delayed making any tweeks until they responded - I'm not a refrigeration expert so I didn't want to cause any harm. I'm happy they responded with suggestions, but geez, why didn't they build the unit to maintain more appropriate freezer temps? What was the tradeoff? It ain't pretty, and it really isn't becoming of a $1600 fridge, but at least it now works to our satisfaction.

[booster]

Originally Posted by peteco

I am pleasantly surprised Nova Kool was responsive to your issues. But I wonder why they have not made the recommended mods a permanent part of the refrigerator. Do they compromise something else? Is it because most users are OK with higher freezer temps???

My understanding is, but I am no refrigeration expert, that the higher the evaporator temp is, the higher the efficiency is, so they likely do it to minimize energy use.



Personally, I don't have an issue with it as far as I know there is no health hazard to it. I think the colder temps just keep stuff in better condition over longer freeze times.


On the way home from our last trip to the Black Hills, DW wanted to bring home a bunch of bison meat products from her favorite meat market in Hot Springs, so we ran the entire frig as a freezer by turning it to the coldest setting and leaving the freezer door open. It held under 20* for two days coming home. For the stuff we had in the frig that we didn't want to freeze, I just put them on the bottom shelf and covered them with a pile of about 3 bath towels to insulate them. They all survived the two days in great condition.

[bwatters60]

Originally Posted by booster

On the way home from our last trip to the Black Hills, DW wanted to bring home a bunch of bison meat products from her favorite meat market in Hot Springs, so we ran the entire frig as a freezer by turning it to the coldest setting and leaving the freezer door open. It held under 20* for two days coming home. For the stuff we had in the frig that we didn't want to freeze, I just put them on the bottom shelf and covered them with a pile of about 3 bath towels to insulate them. They all survived the two days in great condition.

Great idea!

[booster]

Originally Posted by bwatters60

I replaced the Dometic RM2554 3-way fridge in my '08 RT 210P with a Nova Kool R5810 (AC/DC model with Danfross compressor) last summer. We've never run short on battery, but we generally don't stay in one spot more than one night when boondocking. So while I had the RT parked for a few days (without staying in it), I decided to test my batteries. I charged the batteries then started and ran the fridge for 12 hours, rested the batteries for one hour, then restarted and ran the fridge for another 12 hours. In summary, I was pleasantly surprised at how well the batteries (2-6V Duracell 235AH) performed and more or less confirmed my calculations that we'll have ample power for our 12VDC electric blankets.

More good information for everyone to see, and with good explanation of how it relates to your particular use patterns.



You used about 30ah in the first 24 hours including a cooldown, which sounds about right for that frig in moderate conditions.


How much power do the 12v electric blankets take? I assume they can ge quite variable depending on how cold it is in the van?


You appear to be a perfect candidate for a battery monitor, which would tell you all of this stuff without any effort.

[bwatters60]

Originally Posted by booster

More good information for everyone to see, and with good explanation of how it relates to your particular use patterns.



You used about 30ah in the first 24 hours including a cooldown, which sounds about right for that frig in moderate conditions.


How much power do the 12v electric blankets take? I assume they can ge quite variable depending on how cold it is in the van?


You appear to be a perfect candidate for a battery monitor, which would tell you all of this stuff without any effort.

Thanks. The electric blankets use about 50W each, same as the fridge. I switched to 12VDC blankets after finding out the hard way that our 120VAC blankets didn't like the modified sine wave output of the TrippLite (I seem to recall that resistor 21 fried within a minute or two in both controllers). I installed a couple 12V ports near the bed so this works out much better than having the inverter on at night.

I do have a battery monitor installed (pic attached - a cheap one that seems to work well), right above the bed so I can easily assess the battery situation before lights out. So recording periodic voltage measurements is easy, but I could probably be more precise by recording watts consumed. Before replacing my 3-way fridge with the Nova Kool I did the electrical analysis to estimate if we would have adequate power for at least one evening of dry camping. And of course before investing in the DC blankets I updated my projections. My tests are to validate my calculations and also give me confidence in knowing what my batteries can handle.

[RossWilliams]

We have a Roadtrek with at 240 watt solar panel and a Norcold compressor refrigerator. The refrigerator seems to run forever as long as the panel is in the sun. It only uses 36 watts on 12 volt which is where we leave it. That would mean 864 watt/hours if it ran continuously all day, which of course it doesn't. Its possible in some circumstances the solar panel would not provide enough power, but it would be unusual.