Dometic CFX-40W Fridge

[xeon]

You have done a lot of work and lots of testing. When I get into the wondering of why voltage varies at one spot vs another I have to decide if it's worth the fight to figure it out. I am guessing the answer is yes for you. I was a test engineer for TRW safety systems many years ago....so conditions and equipment are my first things that have to be reviewed.

1. Did you use calibrated equipment for all your measurements including temperature while conducting the test. (was outside air temp and pressure the same for all measurements)
2. Did you test the temperature of the battery or the load at the time of the test.
3. Did you measure the resistance of the combined 40 feet of wire?
4. Did you measure the resistance of the wire with any terminals or connectors?
5. In your measurements did you include error variance for your measuring equipment?
6. What is the resistance of the voltage meter? Depending on type of voltage meter are you using? Inductive or direct contact?
7. How new is the jeep battery. Mine is less than a year old and having it replaced now under warranty. its a terrible battery.

Those are just my initial questions to help get you to an answer.

But I think the bottom line is you are getting a voltage reading from the Dometic WiFi app. So additional questions are needed.
1. Where does the WiFi App get its measurement from?
2. Have you opened your Dometic to get that exact location and measure the same voltage location? if no, then we might want to consider the fact that the app voltage read out may never be the same as an external measurement.

I chased this similar line of questioning when I installed mine and came to the conclusion.... I just want my Jeep to start when I get back....if I am late and the food goes bad...don't care, just want to get home. So I dumped the idea of hooking it up to the car battery entirely. Use a yeti and solar panels and I can be gone for as long as I want. But thats me.

If you are taking you readings from the actual rear connector of the fridge by some method and you know the losses related to the wiring and your meter (if any) you should be able to count on that measurement for your successful install.

Now for my experience with the Dometic Settings of High, Med Low kickoff. I don't believe the app is telling you the voltage at the terminal at the back of the fridge. I really think it s an internal voltage point who's number will be different. Again, I haven't torn one apart to verify so maybe you can let me know. However I have found that the fridge is far more sensitive to shut downs based on the thermal load and external temperature. Makes sense. Large loads require less frequent draws to maintain the temp thus make it easier for the battery to do its job. Less use, cooler battery. Cooler battery...better performance and ability to maintain its voltage.

So this is where our experiences are going to vary. Using the Yeti 1000 with setting in Hi... the fridge will go off at roughy 50% of battery life in the Yeti. On Low.... It will work until its down to about 5%. So unfortunately someone else will have to answer what is best for them on their car battery setups.

Given Dometic only provides four settings, its really going to be up to you as to your comfort level with each. I would just suggest starting on Hi....see if thats long enough for your excursions....if not....drop to medium...see that fits. If not....forget the car battery and get a different power source. Thats where I landed.

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[Akbill]

Thanks for detailed reply. not calibrated and I don’t have most of those measurements .
my main concern is that the protection settings dont offer a practical setting given the lower voltage reading in the fridge vs actual battery state. the difference between low and medium settings is huge. mine shuts down on medium setting leaving my AGM 75AH starting battery with a voltage of about 12.1V once the fridge shuts down. the jeep would have to be started at that point to raise the voltage enough for fridge to restart. the low setting however would drain the battery too low to start jeep.
here are settings:
low switchoff 10.1, restart 11.1
medium switchoff 11.4, restart 12.2,
high switchoff 11.8, restart 12.6
manual warns dont use low setting with starting battery, but I am forced too do so.
maybe I should return this fridge......
I am waiting for answers from dometic and the amazon seller SideKick.

 

[xeon]

Well, I hope you find a suitable answer and a solution. Perhaps Dometic has a way to allow you to update its software to change the set points for the fridge to get them where you want them. Alternatively, you may just want to consider a different battery setup. There are some good dual battery setups that are worth considering. Then you can just run the fridge off one battery and not worry about the ability for the Jeep to start. There are lots of solutions, just a question of which one is going to be right for you. The fridge and the way you plan to use it, is just one of several variables you have to consider along with duration the fridge will be on battery. The longer you need to use the fridge on battery...the more a secondary or auxiliary battery makes sense. It will be the same struggle with any fridge or brand. The duration to cutoff may vary but that time difference is going to be small forcing you into a secondary power solution regardless of fridge make or model. Consider a lithium battery and solar panel and you wont have any issues...my two cents. But I am sure you will find a solution that makes sense to you.

 

[Akbill]

Well, I hope you find a suitable answer and a solution. Perhaps Dometic has a way to allow you to update its software to change the set points for the fridge to get them where you want them. Alternatively, you may just want to consider a different battery setup. There are some good dual battery setups that are worth considering. Then you can just run the fridge off one battery and not worry about the ability for the Jeep to start. There are lots of solutions, just a question of which one is going to be right for you. The fridge and the way you plan to use it, is just one of several variables you have to consider along with duration the fridge will be on battery. The longer you need to use the fridge on battery...the more a secondary or auxiliary battery makes sense. It will be the same struggle with any fridge or brand. The duration to cutoff may vary but that time difference is going to be small forcing you into a secondary power solution regardless of fridge make or model. Consider a lithium battery and solar panel and you wont have any issues...my two cents. But I am sure you will find a solution that makes sense to you.

good points, I guess any use long enough to either cause me to run engine to charge up, or to trigger fridge to cut off battery would be once ot twice a month at most. I will just monitor voltage and manage it on the low protection setting. I put in a cool outlet with 2 usb plugins which constantly shows the battery voltage on tiny led display. It draws 9.6 milliamps (less than a fourth of an amp in 24 hours), but it makes it easy to monitor battery.

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