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Old 01-26-2017, 08:28 AM   #1
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Changing temp setting on fridge

My wife is generally smarter than I. She turned down setting on Dometicfridge since eggs had frozen. Result is that battery suite is at 65% SOC in the morning instead of 50 to. 55% (LFP batteries). We are at a lovely RV park in Patzcuaro, Michoacán, Mexico which has decent electricity but we choose not to chance overcharging the batteries. The system should not allow this to happen but we are very cautious.
Reed and Elaine
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Old 02-06-2017, 01:15 PM   #2
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SOC is state of charge, that is your batteries are less discharged at 65% versus 50-55% you are correct about your wife
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Old 02-06-2017, 01:22 PM   #3
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Originally Posted by Reed Cundiff View Post
My wife is generally smarter than I. She turned down setting on Dometicfridge since eggs had frozen. Result is that battery suite is at 65% SOC in the morning instead of 50 to. 55% (LFP batteries). We are at a lovely RV park in Patzcuaro, Michoacán, Mexico which has decent electricity but we choose not to chance overcharging the batteries. The system should not allow this to happen but we are very cautious.
Reed and Elaine
I agree your wife is generally smarter.
I am a little confused at this though. Are you running the Dometic fridge on 120v power or propane and 12v power?
If running on 12v something doesn't add up in my mind.
If running on 120v then it makes more sense.
Or it is also possible you have a really small LFP battery bank.
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Old 02-07-2017, 07:26 AM   #4
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LFP battery suite

The Dometic is a real energy hog. It draws about 12 amps at 12 V or nearly 150 W. our battery suite is two Manzanita Micro 180 A-hr (12 V nominal, 13.8 V actual) = 360 A-h). This is 4300 W-hr at 12 V nominal which is a decent battery bank for a Roadtrek. We could switch to a Stirling cycle fridge (aka marine or commercial) for greater electrical efficiency but the cost is not worth it, and would not be able to use propane
Reed and Elaine (north of Puerto Vallerta)
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Old 02-07-2017, 05:52 PM   #5
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Computer guy why does it make sense that his fridge is freezing stuff if it is running on shore power?
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Old 02-07-2017, 06:02 PM   #6
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Computer guy why does it make sense that his fridge is freezing stuff if it is running on shore power?
My comments were related to the power usage vs SOC quoted not the frozen egg. The gist of the original post was the fridge was too cold and then it was adjusted a bit (by a very smart wife) to make it less cold. The 10-15% difference in SOC is a big number to save so it led to my comment. There are more inefficiencies by an inverter which might lead to higher battery usage and typically a residential fridge will also use more power.
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Old 02-07-2017, 06:21 PM   #7
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I only asked because my frig likes to drop below freezing I installed a digital thermometer with the display outside the frig so I can keep an eye on it
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Old 02-07-2017, 06:24 PM   #8
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The frig is the 2 way frig I've been running it on shore power
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Old 02-08-2017, 07:23 AM   #9
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Do not trust shore power in Mexico since it is often not grounded so we run D.C. during day and propane (butane down here) at night. The Dometic is absorption cooling which is efficient with propane but not with electricity. Stirling cycle fridges are quite efficient with electricity
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Old 02-08-2017, 11:42 AM   #10
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Do not trust shore power in Mexico since it is often not grounded so we run D.C. during day and propane (butane down here) at night. The Dometic is absorption cooling which is efficient with propane but not with electricity. Stirling cycle fridges are quite efficient with electricity
Reed, I understand your point entirely on this.

IIRC, it is possible to use an isolation transformer and your own ground to reduce this problem. An isolation transformer is nothing more than a conventional transformer with good insulation to be sure that there is not a connection between the primary and secondary windings.

Essentially you are creating your own ground and neutral reference.

Another option that I actually prefer is to use an external AC-DC converter. Plug the AC into their power supply and DC into your rig. Ground the converter pin yourself with a stake into the ground.

I think that Xantrex makes a very wide input range charger family (wide both in Hz and voltage) to make the connection aspect easier. The price is 2x what IOTA charges for similar capacity, but narrower input range chargers but perhaps it is worth it. I am still looking for other domestically produced, lower cost options but have not found any yet.
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Old 02-08-2017, 02:58 PM   #11
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What was the question? Is it running on propane, 12v or 120ish volt?

My head hurts
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Old 02-08-2017, 04:34 PM   #12
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Harryyn - will ask our son about your concept. He is a Master Electrician as well as being the first (1991) licensed alternative energy contractor in NM. We only operate from battery suite via PSWI and 12V and so only charge with battery charger if we do use shore power (we burned out a microwave in Baja and another in Yucatán due to widely varying voltage. The problem with ungrounded is that Roadtrek chassis becomes "hot" and one gets moderate shock when touching and body is grounded.

So will grounding chassis/frame ameliorate this? Again, thanks for advice and will run by son. We shall not be back in US for four or five weeks. So thanks again for idea

Garbanz - the answer is "yes" I.e. The absorption Dometic fridge can run on propane (butane in souther Mexico), AC, or D.C. We run it in DC from solar to avoid inverter inefficiencies.

Reed and Elaine (north of Puero Vallerta)
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Old 02-09-2017, 11:41 AM   #13
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Reed, I am not an expert, but your symptoms sound a lot like the dreaded "hot skin" effect that comes from the neutral to ground wire bonding being incorrect "somewhere" in the path. This problem shows up in marinas all over the place, including in the US and people are unfortunately routinely electrocuted every year swimming near docks.

If you don't have the problem when plugged into a US grid plug, it might in fact be related to the way wiring is done in Mexico (or many other places)

Again, I am not an expert on this area, but my understanding is that it relates to the idea that the neutral and ground wire can only be connected in one location in a circuit. In the US, when connected to the grid, it is at the breaker panel.

When "mobile", there is a transfer switch function that recreates this neutral / ground bond point somewhere inside of your van - often inside of the inverter. Some inverters do this, some don't.

My understanding is that by using an "isolated circuit" - either via the isolation transformer or fully isolated DC power supply, you are sort of creating your own distinct "grid" and can set the "van skin voltage reference" to whatever you like - including truly ground that you walk on.

I am very interested to hear what you son has to say about the subject area. In fact, I would not mind hiring him for his opinion on some projects.
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