Replacing NorCold N811RT with residental refrigerator

[sc4668]

Hi:

  Looking for some advice or accrual experience on replacing the N811RT NorCold with a residential refrigerator.
I have a 2007 Denali 31ft Fiver. On a month long summer trip the refrigerator did not cool real well. We do not boondock except an occasional rest stop layover while traveling. We do not have a generator or invertor and only 2 12 volt deep cycle batteries. Here are my questions.

1) what will I need for batteries
2) What watt invertor do I need
3) what amount of time will the batteries last with just running the refrigerator
4) How many have done this, how hard for a DIY and do you think it was worth it
5) Pros and Cons for this conversion


We are planning a couple month trip this summer heading back east from Las Vegas.

Thanks for any information provided.

 

[Gary RV_Wizard]

There is a lot of variability based on how you use the fridge, climate, etc, but a newer residential fridge doesn't actually use much power. Think in terms of 200-300 watts to operate the compressor and double that briefly when the ice maker cycles. The harder question is how much does the compressor run? That depends on temperatures, how often the door is opened, how much food is inside (vs open space), etc.  Most Rvers find that 20-30 minutes per hour is sufficient, on average. That's about 70-150 watt-hours per hour or up to 1800 watts-hours per 24 hour day.  Worst case, powering that  via an inverter @ 12v means a full day use could suck 1800/12 amps from the batteries, so 150AH  That's about the total capacity of two Group 24 12v batteries. Best case, though, is well within reach at 560 watt-hours and 560/12 = 47 amp-hours. Quite a range, so the details of the assumptions are important.

Some members here have installed modest 10-12 cu ft residentials in their rigs and can probably give some fairly firm estimates. I'm guessing 2x 12v batteries will be fine if you don't stay off-grid much. However, I'd plan on upgrading to two 6v golf cart batteries, which will increase capacity as well as handling the amp load better (and last longer). You would need a 800-1000W inverter as well.

As a DIY project its not challenging at all - just basic handyman skills.

 

[Lou Schneider]

Another factor in how much power the refrigerator will use is where it's condenser (heat radiating) coils are located.

Traditionally they have been in the open on the rear of the refrigerator.  Here they are dumping the refrigerator's waste heat into the same area as the RV fridge and they will work just fine.  You will have to create a seal around the cabinetry in front of the refrigerator where the original fridge sealed to keep drafts out of the RV interior.  I just ran a layer of high quality duct tape across the gap between the refrigerator and the face of the cabinet to create the seal, then covered it with wood trim.  The tape also helps hold the refrigerator in place.

Other refrigerators have their condenser coils mounted underneath, and exhaust this heat plus the compressor heat out the front of the refrigerter, into the inside of the RV.  With these you can seal up the space behind the refrigerator and not worry as much about drafts coming in.  But you do need to keep the vent space underneath the refrigerator open so the heat can freely exhaust.

You can improve the insulation on either of these refrigerators (lessening the amount of time the compressor runs, thus saving power) by filling the space between their sides and top and the cabinetry surrounding the refrigerator with solid foam or fiberglass insulation.

A third kind of residential fridge mounts the evaporator in the side walls, under the sheet skin.  These can NOT have airflow restricted around the sides of the fridge as it relies on radiant heat and convection to move the heat away from the fridge. Their instructions will usually say the fridge must have an inch or two of free space around it to provide adequate airflow.

Mounting one of these in an enclosed cabinet will lessen the efficiency as the refrigerator will have to work harder to transfer heat outside of the box.

As far as battery life, figure on about 24 hours for two batteries along with other modest usage.  The limiting factor won't necessarily be the battery's depth of discharge, but the inverter tripping off due to low voltage during the compressor's starting surge.

You can minimize this (and maximize your run time) by mounting the inverter as close as practical to the batteries and using thick wire to connect them, minimizing the wire's voltage loss.  You don't want to put the inverter in the same compartment as the batteries due to the corrosive battery fumes, but mounting it on the other side of the compartment wall is fine.  Then run the 120 volts to the refrigerator.

 

[kdbgoat]

To run down the road with no power to fridge, try a gallon jug of frozen water in the freezer and refrigerator sections. That will probably be enough to hold you over if the fridge and contents were already cold/frozen to start with. Just don't open the doors any more than necessary until you get plugged back in.