I have a 10-year-old Engel 43-qt frig/freezer with the Sawafuji compressor. This is a single-compartment unit, so it is a refrig OR a freezer, unlike your Dometic frig/freezer, which has a separate freezer compartment. Currently we are using our Engel as a home freezer.
It has an uncalibrated thermostat. Since we use it as a freezer, I simply set it to MAX COLD and let it run. It has settled at a temp of about -5 degrees F. This is in an ambient of 75 degrees, with no direct sunlight on the unit, and good ventilation for the cooling mechanism.
When the compressor is on, it draws about 2.3 amps on DC power. In the conditions outlined above, the compressor seems to run about 60% of the time.
So what does all this mean to you? My intent is to highlight the things that will have an effect on your unit’s energy consumption.
The factor that influences energy consumption the most is the thermostat setting. In other words, how cold do you want the unit to be inside? In my example above, I just set it to MAX and let it run. You can’t be nearly as cavalier about the setting.
If you demand a refrig temp of 35 degrees (in other words, a 40 degree drop from a 75 degree ambient), you will use a certain amount of energy. If you are willing to raise the thermostat to 45 degrees (a 30 degree drop from a 75 degree ambient), then you will cut the unit’s energy consumption by 25%. And similarly in between. This decision is complicated by the fact that although your unit has both a refrigerator and a freezer, it has only one thermostat. This means that you set the thermostat to the temp you want in the refrig, and take what you get in the freezer. If the freezer is too warm, you have to juggle. Get a good refrigerator thermometer.
The next major element in calculating energy use is what percent of the time the compressor actually runs (called duty cycle). It certainly will not run 100% of the time. If the compressor draws 6 amps when running, but runs only half the time, the equivalent current for calculation purposes is 3 amps. And if it runs only 1/3 of the time, then the equivalent is 2 amps. These are the numbers you would use in the battery-life calculations. As you would expect, compressor run time is determined by thermostat setting, as well as by ambient conditions.
Among the other factors that affect energy consumption are ambient temperature - how warm is it in the room? If you park your TM in the shade and open the windows for a good cross breeze, the ambient in the TM will be about as low as you can get it. If you go away for the day and close all the doors and windows to deter thieves, the temp inside the trailer will rise, and so will the energy consumption of the refrig.
Next is venting the refrigerator’s cooling mechanism. The TM’s 3-way refrig generates a lot of heat, so TM uses a relatively big fan to suck the heat out of the refrig mounting compartment. The Dometic 2-way will generate a lot less heat, but it is still important not to let it build up. Otherwise the refrigerator is fighting an uphill battle. Especially on a hot day, it might be wise to have a low power fan built into the compartment.
Along a similar line is sun loading. If you park the TM so that the refrig is in the sun, you are pumping heat into the compartment. You should either park the TM in a different direction, or at very least rig up a sunshade over that area of the wall.
So my refrig draws 2.3 amps DC, while yours draws 6 amps DC. Mine is set for really cold, so the duty cycle is high, while yours will be set warmer, so the duty cycle will be less. Since you are looking at solar as your exclusive source of power, you'll need to be aware of, and manage, the other items carefully.
My apologies for the length of this post. I hope it helps clarify some of the issues under discussion.
Bill
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