12v frig vs. 120v

[jcollins]

It's time to replace my fridge. Presently I have the Norcold 12v model DC 340.

Here are the power specs for the new model.

Power Source
Model Amps 120V/AC Amps 12-24V/DC Amps 24V/DC
DE-0041 0.2 2.8-1.6 1.6

When I'm on shore power it's not an issue. I'm thinking about when anchored.

So, wouldn't it use LESS power to run it on AC with the inverter rather than 12 volt? The inverter is a 2000 watt/1600 continuous and uses 1 volt when turned. on.

[Carl]

John, It doesnt quite work like that. Based on the amps of the fridge, and useing round numbers, I think it will take about 8 to 10 amps to run the fridge off of your inverter.

[RicM]

Anytime you pass power through an inverter you are loosing power. A fridge that works on 12V natively will be more efficient than a 120V unit that you have to supply through the inverter. That said, work done is work done, and the energy expended to get it done is going to be about the same.

[mhanna]

I agree with Ric on the fact that running it through an inverter will create loss.
I would have bet that the total watts to run the unit would have been the same for AC or DC. But according to your specs running it on AC saves ~9.4 Watts. The only reason I can think of the savings is that a part within the unit is just more efficient when running on AC.
AC- 120V * .2 amp = 24 Watts
DC- 12V * 2.8 amp = 33.6 Watts

That being said I will also say that if you run it via an inverter I am pretty sure you are going to waste more than those 9 watts on inefficiencies and heat of the inverter. Depending on the type of inverter (I am guessing you have a modified sine wave) that it could also shorten the life of the unit. See the below link for a quick explanation.
http://www.windsun.com/Inverters/Inverter_selection.htm

The bottom lime is there really is no savings sorry...

Matt

[loubennett]

All of the comments are great from the power consumption side of the equation. The other part is the effectiveness of the insulation. With better insulation the compressor will run less and the average power consumption will be lower. I expect that all the compressors have about the same efficiency so the insulation becomes the real difference in the overall efficiency of the refrigerator.

Serious cruising sailboats use engine driven refrigeration systems. They are expensive, but solve the battery problem. In these systems there is an engine driven compressor that freezes a utectic plate (cold plate). This then acts like a block of ice to keep things cold. With a well insulated box, the compressor only has to be run for about one hour per day. There may be some such systems that use a 12 volt compressor. If money were no object and I spent alot of time anchored, I'd give this a serious look but it would be overkill for my normal use.

[joreyn]

I replaced my Norcold dual voltage unit last winter. It had stopped working on DC, so I rerouted the 120 plug to a receptacle that was attached to the inverter. I was having serious issues with battery drainage when I did that.

I made the decision to go with a 12 volt-only unit. This makes my boat a 12 volt boat for the most part, which works for me because I don't need air conditionaing here in the Northwest. I only need 120 for the microwave, the coffeemaker and the toaster, now. And for the odd power tool.

One thing I spent a good deal of time on was the quality of the refrigerator itself. The Norcolds seemed to be trouble prone, and replacing the cooling unit costs as much or more as a new refrigerator. I ended up selecting a Dometic 12 volt. Very quiet, well insulated, and a solid reputation for longevity. It is also marketed as Tundra I believe.

I simultaneously added two more golf cart batteries to the house bank. This past summer, I've enjoyed very quiet reliable performance and the house bank has been fine with daily running of the engines.

[jcollins]

Thanks for all of your replies. My thought was to get more use out of the inverter. It's a "nice-to-have" item that barely gets use. I am definitely getting an A/C unit this time. It always bugged me to have that constant charge/re-charge on the battery for the summer.
I am looking at a couple of different models. I have the winter layup to shop.

[jleonard]

In my previous boat I replced the Norcold with a Sears 120 V only. I was able to fit the new 5.6 cu ft fridge in the same space as the norcold and that was 3.2 cu ft I believe.
I glued some hard foam insulation panels to the top and sides before I did the installation.
I found I needed a 1000 watt inverter to run the fridge. Get the remote switch for the inverter. I did "eventually".

[jcollins]

In my previous boat I replced the Norcold with a Sears 120 V only. I was able to fit the new 5.6 cu ft fridge in the same space as the norcold and that was 3.2 cu ft I believe.
I glued some hard foam insulation panels to the top and sides before I did the installation.
I found I needed a 1000 watt inverter to run the fridge. Get the remote switch for the inverter. I did "eventually".

I'm thinking along those lines. There is a company named Avanti that makes compact refrigerators. Much less money for the same thing. One concern is balance. The RV/marine refrigerators can be off up to 30 degrees. I don't know about the home/Office type units. I have a call into their tech support.
Avanti makes ALL refrgerator models. I have never used the mini freezer. Wasted space for me.
My inverter switches automatically. No problem there.

[jleonard]

The RV/marine refrigerators can be off up to 30 degrees. I don't know about the home/Office type units

I was off kilter more than 30 degrees many times and the fridge was the last of my worries and it never quit. Although I needed a change of undies more than a cold beer, the cold beer was nice

have never used the mini freezer

Not a bad to have a small ice cube tray. Ice makes excellent company with the vodka and the garlic stuffed olives

[joreyn]

John, I believe most marine refrigerators use a DC compressor. In my research last winter, it seemed like the Danfoss compressor is the most reliable, quiet, and environmentally sound unit. Danfoss compressors are found on Tundra/Dometic units, as well as some other brands.

They offer the option of a dual voltage system which gives prioity to AC when connected to shore power. Or you can go 100% DC. Here is why I chose to go DC, besides the fact that it is whisper quiet, which is what I want while at anchor.

When you connect to the inverter, you are pulling DC power from the batteries to the inverter, and you lose amps in the process. Then the AC power goes to the AC power supply which is located on the refrigerator. At the power supply, it is converted back to DC to run the compressor.
This adds to the loss of energy. All in all, very inefficient, plus you add "wear and tear" to the inverter.

The AC power supply is an add on option. If you are going to be on shore power a lot while cruising it makes sense. If you mainly use the refrigerator while out cruising with occasioanl shore power connection, maybe DC only is the way to go. Your batteries get charged while you are underway, as well as when you are on shore power.

Check out http://www.dometicenviro.com/marinerefr ... frige.html for useful information, plus a link to a coversion table that shows which model will go into the cutout from your old Norcold.