Replacing Norcold 3-way with 12V compressor fridge in Model S

keithp

After several weekends with above 90F temps, I'm frustrated by my Norcold 3163 not managing to keep things at a reasonable cool temperature. In the afternoon, it would reach about 50F. Yes, I've got the cooling fan added to the exterior vent, but it's still not doing the job. I'm considering replacing it with a 12V compressor fridge using the Danfoss DB35 compressor. Benefits would be increased reliability, better cooling capability, a freezer (ice cream!), power consumption on the road (I use 12V for cooling en-route) and a smaller package for the same cooling volume. Drawbacks are price (these are all ridiculously expensive), and power consumption while stationary.

There are lots of options, and I've narrowed down the search to those which will fit in the existing opening. That's a pretty hard limit, with 24" of height (and a pressure regulator from the stove partially impinging on that), 24.5" of width and depth ranging from 17.5" at the bottom to 21" in the middle. Here's what I've found so far:

1. Thetford NR740 (20.5 x 15.25 x 17.875 - 1.7 cu ft).
   
2. Engel SR48F (20.39 x 15.12 x 17.67 - 1.4 cu ft)
3. Nova Kool R1900 (20.675 x 15.675 x 17.75 - 1.9 cu ft)
4. IndelWebasto Cruise 65 Elegance (20.75 x 17.75 x 18.5 - 2.3 cu ft)
5. VitriFrigo C60IBD4-F-1 (24.5 x 19.125 x 16.125 - 2.1 cu ft)

The last is probably ruled out because of height, but it's the only VitriFrigo unit that's even close. There are lots of others similarly sized in height at just over 24 inches that I didn't bother to include. The IndelWebasto unit is 18.5" deep maximum, but has a sloped back which looks like it will fit. As such, it seems like the best one in the list, filling the largest amount of the existing area while providing lots of space inside.

IndelWebasto also sells a add-on control module for the DC-only model that is supposed to make the unit use less power on average by letting the temperature rise a bit when the voltage indicates that it's running on battery without any charging.

In any case, all of these use the same compressor, which draws about 40W when running. It's pretty hard to know what the average power draw would be as that depends on the outside temperature and the quality of insulation around the box.

I'm interested in hearing from anyone who has done this or is thinking about it.

Sharon_is_SAM

How do the 12 volt units perform in +  90 degree temps?

keithp

SAM said:

How do the 12 volt units perform in +  90 degree temps?

I'm still looking into that; they're compressor based, and don't require pre-cooling before use. I'm hoping that means they've got a lot more cooling capacity than the absorption units. This comment from someone using the Indel Webasto unit on a boat says that work at up to 40C, which is 104F.

jcfaber1

The compressor units work just like any other electric fridge.  We have the 12V fridge in our 2007 and it works just fine.  You do not need to care about being level, or at what elevation you are at either.  The one's you are listing use the same compressor as the ARB that many on this forum use(myself included).  My fridge is older and find it just does not use that much juice and what you are looking at will be even more efficient.  I have never lost any food with the fridge or our ARB.  You just have to get used to the idea of managing your battery.  Sure marine service will discount the Vitrifrigo so be sure to call.  I looked at the 130 liter Vitrifrigo unit which would go under the stove and where the coolcat now resides.  My problem is how to add another AC unit elsewhere in the t@B.  The lack of fridge space is my big gripe with these fantastic  little campers.
John

keithp

jcfaber1 said:

The compressor units work just like any other electric fridge.  We have the 12V fridge in our 2007 and it works just fine.

Thanks for the info; it's good to know other people have similar devices that work fine in the t@b.

Michigan_Mike

SAM said:

How do the 12 volt units perform in +  90 degree temps?

I love my 55 qt. ARB and it doesn't miss a beat in the heat!  

Sharon_is_SAM

Mike, us too, but even ARB issues a warning that it will only cool 50 degrees below ambient.  We have not taken ours out with sustained temperatures in the CS galley.  Keeping our fingers crossed.

skwhee

@keithp
Here's an excellent article on the pros and cons of a Danfoss equipped 12V RV refrigerator:

http://www.truckcamperadventure.com/2016/02/the-danfoss-compessor-refrigerator-pros-cons-and-a-few-tips/

Since the development of the Danfoss in 1998 and great improvements in battery and solar technology, it seems the RV industry is slowly migrating away from ammonia absorption (3way) refrigeration.

From a personal point of view we had an excellent experience for three years in our custom T@B-CS with the Norcold NRF-30 Chest Style refrigerator that nüCamp uses in their T@G trailers. The Norcold website doesn't specify which compressor it uses but does say that it has a 4.3 amp draw on 12V. It's on the small side with a 1.1 CF (33 qt) capacity but we always managed well with it during our 6-8/months a year on the road. During that time we were equipped with a Group 24 or Group 27 wet cell battery. You really need more to comfortably camp off grid with a 12V refrigerator.

Now we're traveling in a T@B-400 that comes equipped with the Norcold NR751 with the Danfoss compressor:

http://www.thetford.com/product/nr751/

And a 235 AH AGM Discover battery:
http://discoverbattery.com/product-search/view/EV4DA-A

We still need to upgrade our solar capabilities. We do marginally well with our Zamp 80W panels but more generation would be nice.

The Norcold NR751 with it's 2.7 CF (80 qt) capacity has done an excellent job these last three months keeping our food consistently cold even when the temperature inside the trailer exceeds 100F and it gives us plenty of room for groceries and a few beverages.

Good luck with your conversion. We feel confident that you will be glad you did.

MAG

Does anyone know the dimensions of the Norcold 3163 ??? 

TabberJohn

From the install guide (pg. 3)--
The following dimensions will allow the installation and removal of the refrigerator. Also, the dimensions provide the necessary clearances for air circulation around the refrigerator cooling system.
Refrigerator Enclosure Cut-Out Dimensions --
Height x Width x Depth: 24 1/8" x 25 5/8" x 16 7/8"

MAG

Thank you TabberJohn.

MAG

Once again TabberJohn thank you, my page 3 has nothing on it like that, so I am really glad yours does. Thanks for your help. Stay tuned in as I might need your expertise again.