Please help me calculate power needs

[okmunky]

I confess that I'm pretty clueless about the true difference between the amount of power it takes to run a compressor refrigerator, specifically an AC compressor on a 1500 watt MSW inverter vs a 12V DC compressor (Dan Floss?)

Please help me figure out the actual difference between these 2 options -

#1 replace cooling unit in my currently installed 6 cf Dometic propane/AC fridge with an AC compressor cooling unit from Products | JC Refrigeration and a 1500 watt inverter.
Total cost ~ $650
Specs - Converts existing fridge to a residential fridge (which eliminates LP gas). This cooling unit is built with a compressor system and not only do you get to keep your same fridge and controls you are used to, but there is no need to remove the windshield or window to get the old fridge out and the new in – nor the hassle of cutting or redoing the cabinets to make a new fridge fit. Also there is no need to have the coach perfectly level for the fridge. It pulls less than 1 Amp and will run off a 1500W inverter (does not require pure sign wave). This unit is coated with a corrosion/rust preventive paint, and is very user-friendly to work on in the field should it ever need repair in the future. It is designed to withstand hot/humid temps and will keep your ice-cream hard. Comes with a 3-year warranty.

#2 replace entire refrigerator with a Dometic Americana DCM 2841 - 8 cf
https://www.dometic.com/en-us/us/pro...a-dmc-_-143818
(AC/DC compressor cooled) same cabinet dimensions.
Cost ~$1200
Specs-
ELECTRICAL
Input voltage (AC) 120 V
Input voltage (DC) 12/24 V
Rated input current (AC) 1 A
Rated input current (DC) 9.6 A
Rated input power (AC) 70 W
Input frequency 60 Hz

So how many DC amp hours would each of these require if they run 25% of the time? Which option would you consider best for boondocking?

Thanks for your help and patience!

[Spdracr39]

I would stick with a 2 way refrigerator. I want the ability to run it either way.

[C.Martin]

Unless you have a data logger...you really cannot compare the two.

I will say your estimate forgets one thing. In addition to the Inverter, cables, etc... if your coach was balanced around a Propane capable fridge before...you might need more batteries and bigger converter too.

[Sbrownstein]

Both units have AC compressors, the Danfoss is also a variable speed compressor with a built in inverter. Runs AC or DC for input. Most good units today have inverter powered compressors for variable speed. I would pick the one you are most comfortable with, either will probably use the roughly the same amount of energy, although a new appliance will probably have improved insulation.

If you are used to boondocking on an LP reefer, you might check your battery capacity. Roughly 12 Hours on two 100 AH batteries, 24 hours on 4.

[twinboat]

The Dometic specs say it draws 9.6 amps@ 12 volts when running.

Divide that by 4 for your suggested 25% run time per hour and that is the amp hour use. That's about 2.5 AH times a 24 hour day is 60 AH.

You will need to add inverter losses of 12 % and inverter idle time draw.

They also say that MSW inverters are 30% less effecent running electric motors then PSW models.

I use a Xantrex Pro Watt 2000 PSW inverter on my residential fridge because it has a low idle draw of 1/2 amp. Some draw 2 to 4 amps and that can add 48 to 96 AH a 24 hour day to your calculation.

IMO, A stand alone 1000 watt, PSW inverter, with a low idle draw is the best way to go with 120 volt fridges. Plug the TV into it and leave the big inverter off unless needed.

[Sbrownstein]

Twinboat is correct. i was using the average load of my 22 cuft Frigidaire. 24 hours on two, 48 hours on 4 batteries. 1000 PSW Xantrex is reasonably priced and does have very low idle current.

[okmunky]

Thanks guys! After doing some of the math and realizing how important the refrigerator is to us. (Sena is on insulin) I decided to go against my parents thrifty, save every penny teachings. The bottom line is that everything else in my current fridge is 7 years old - 7 fulltime years. What will quit on it next?

I ordered a Nova Kool RFU 9000 DC compressor refrigerator. I'll pick it up in Seattle in about 6 weeks. I estimate it will use about 32 amp hours per day which is very doable for us.

Nova Kool RFU9000 9.1 CU FT DC Only Two Door Refrigerator & Freezer