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Old 04-27-2008, 02:56 PM   #1
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Refrigerator power

We are leaving next Saturday for three weeks in the Sportsmobile. I have no experience with RV refrigerators. Am I correct in thinking that the fridge will run on the house batteries if not plugged in anywhere? If I plug in to shore power or a generator does it switch to AC 110 or does it stay on 12 volt DC power? Generally speaking, how long can it run on the batteries without draining them? If I plug into shore power or a generator do all (house and vehicle) batteries charge automatically? Lastly, if I drain the house batteries will I drain the vehicle battery also, preventing it from starting? Thanks. oclv
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Old 04-27-2008, 04:51 PM   #2
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refrigerator

I'm not sure which year your SMB is so I'll tell you about mine. My refrig. is 12v DC and runs off the house battery only. If I'm plugged into shore power that will charge my house battery & chassis battery if needed. I also have a solar panel which will do the same if the sun's fairly high and i'm not parked under a tree or something. How long you can run the refrigerator depends on the setting. If you don't use the freezer and stuff it full of newspaper or some such material, you can run the refrig. at a lower setting. I'm really not sure how long my one house battery could run it, because the solar panel is always charging it. (hopefully) lastly, if I drain the house battery, it should still start. If I've missed anything or misinformed you, hopefully someone will point that out. Hope I've helped.

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Old 04-27-2008, 06:38 PM   #3
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As noted, it would be helpful to know how your SMB is configured since there are a large number of possibilities.

First, what refrigerator do you have? You can have a refrigerator that runs only on 12vdc, “dual-electric” that run on both 21 vdc and 110vac, and “three-way” that have both electric modes plus propane. You can figure out what kind you have by getting the model number off of the plate inside the refrigerator and using a search engine.

If you have only 12vdc, then it runs off of the house batteries. While you drive, the alternator keeps the batteries charged, but when you stop, that’s it and the refrigerator then becomes a drain. Most SMBs also have either a converter or inverter/charger. A converter will allow you to park, plug in to shore power, and then feed dc power to the house battery, keeping things running indefinitely. You might also have an inverter (that changes 12vdc to 110vac) that has a battery charger feature that will give you the same result as a converter when on shore power. Solar will do what the converter does – feed 12vdc to the house battery – but of course only while the sun shines. If you have a generator, it would be wired into the converter to charge the house battery while it is running.

If you have a dual-electric, as I do, then whenever the van is plugged into shore power there is a direct feed of 110vac to the refrigerator and it stops running on 12vdc. This is important because the refrigerator is much better at cooling things down when running on 110 vac. If we are taking a trip and the refrigerator is not already on, I try to plug into shore power for 24 hours before we go and crank the refrigerator up high to chill it down.

The three-ways allow you to run on propane when not connected to shore power, and I understand that they are less efficient when running on 12vdc than a dual-electric.

Your van batteries are normally kept separated, or isolated, from each other during discharge by a battery isolator or battery separator. There has been a fair amount of discussion here on the current separator used by SMB, but I don’t know when they switched from one type to the other, but your van should certainly have one of these devices. Whichever you have, it will prevent the starting battery from being drained if the house battery is drawn down. (Note, though that there is an exception for the “van radio” switch discussed at length elsewhere).

How long you can run just on battery power depends on a bunch of things: the draw of the refrigerator, how cold you set it, how often you open it up, how hot it is outside (keep direct sun off of it), and the size of your house battery. Refrigerators have gotten a lot better. My SMB replaced a 20-year-old VW Syncro with Norcold’s dual-electric predecessor to the current models. It had an 8D 255 AH house battery (a bit bigger, actually, than the “big” SMB 4D battery currently sold), and a 80w solar panel on the roof (the current Kyoceras sold by SMB are 130w). We found that in moderate to warm weather we could stay out for 2 days without shore power or running the engine and not stress the battery (most recommend avoiding draining more than 50% of the battery before recharging). My new Norcold uses less than half of the amperage than that old Norcold, even though it is considerably larger. Don’t forget the other draws on the house battery, as they mount out. Unless you run a microwave, TV, big audio system, or other large energy hog, though, the refrigerator will be the biggest consumer. A lot of us, though, have a lot of electric toys in our SMBs, so keep an eye on things.

It takes a while to get the feel for this, as I know from a couple of unpleasant experiences. If your trip involves a lot of driving, you should be fine as the alternator will keep things going. If you are staying put, though, you will probably need some additional power, whether solar, shore, or generator, after a couple of days.
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Old 04-28-2008, 09:09 AM   #4
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Thanks for the helpful information and tips. I took one of the tips and went on line and got an owners manual from Thetford/Norcold. I also like the tip regarding plugging the van in before leaving for a trip to get the refrigerator cold and charge up everything. My refrigerator is a DC 0051, electric only (no gas). It runs on DC unless 110 AC is available in which case it defaults to this. Neat. Thanks again. oclv
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Old 04-28-2008, 02:40 PM   #5
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Before we got solar, we always plugged into shore power and turned the refrigerator on before a trip. Now with solar, the shore power cord is stored deep under a lot of other items and we haven't used shore power in several years, even when it might be available (which is rare for us). It is also VERY important to precool everything going into the refrigerator...don't put warm soda cans directly in it. If you restock during a trip, only add a couple of uncooled items at a time. If you put too many uncooled items in at one time, the temperature will go up and the refrigerator will never catch up.

You should be able to tell if your refrigerator is running from shore power by listening while you plug in to shore power. Turn the refrigerator on (or turn it cooler) so that it is running. Continue to listen to it while someone else plugs in to shore power. If you hear the frig shut off for a second and then come back on, it is being powered by shore power while plugged in.

A remote thermostat (such as the indoor/outdoor ones with a remote sensor) are invaluable for our refrigerator. Unlike a home refrigerator, temperature control isn't completely automatic. You might start out with a too-cold setting before loading it up (even if you are quite quick, it will lose several degrees just putting stuff in it) and then turn it down a little so that lettuce doesn't freeze. We have also found it necessary to turn ours down at night and turn it up during the day if it is hot. The remote thermostat lets you keep track of the temperature without continually opening the door.
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Old 04-28-2008, 07:10 PM   #6
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when powered...Run your fridge loaded with food and a bag of ice in the fridge, set to coldest possible.
- Then on battery, turn to lower setting to reduce cycling. Open door as little as possible and do not put warm/hot items inside

In warm weather my 4CUFT fridge stays cool for 24 hours on 2 older house batteries. No solar, but I can run the generator if desired.
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