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FightinIrish
09-20-2007, 05:31 AM
I read somewhere on here that a possible aid to keeping the refrigerator cool when traveling but not using the tow vehicle's battery, 12V, is to place some dry ice in the freezer. Is this an acceptable means to take the chance of forgetting to unhook the TM from the TV if you go into a restaurant or rest area while traveling?

Bill
09-20-2007, 08:08 AM
Dry ice is fine, although it is so cold that you run the risk of freezing everything in the refrigerator as well as the freezer. Some people say you can wrap the dry ice in a towel to prevent so much cold from being produced. I've never tried it.

Let's be clear about one thing. If you make a 15-minute stop at a rest area , it won't discharge your tow vehicle battery to any degree. Similarly, a one-hour restaurant stop won't hurt anything, provided that your tow vehicle wiring is heavy enough to recharge the battery when you get on the road again. Most are, but some are not. You didn't mention what your tow vehicle is, so no one can answer that question for you. It is the eight-hour stop at Disney World that is a battery killer.

Finally, if your tow vehicle has a battery isolator, the tow vehicle battery won't discharge at all when you stop. The TM battery will discharge, of course, but regarding the tow vehicle, all of the above still holds. Does your tow vehicle have an isolator? Most do, but some do not. Again, since we don't know your tow vehicle, we can't tell. But it is easy for you to determine if it does - and easy to add one if you are at all handy. The procedure for checking has been outlined several times here on the board.

Bill

PopBeavers
09-20-2007, 09:26 AM
I would be concerned that dry ice might make the plastic of the fridge brittle and subject to cracking. I would not do that. If you want to use dry ice, use it in a 50 dollar cooler.

Get an isolator or a relay. Set it and forget it. Just keep the TM plugged into the TV at all times.

I never forget to plug the TM back into the TV. After every stop I perform a walk around inspection. I am pretty srue I would notice the dangling cord. Every time I start the TV I turn on the headlights and verify in my rear view mirror that the lights on the TM come on. Then I turn off the lights. I also tap the brakes and verify that I do not get an Open Circuit warning.

countrygirl
09-20-2007, 01:32 PM
We use dry ice every year bringing home meat from Missouri. All contents of our cooler will stay frozen for up to 2 days provided we do not open the cooler. I think it would freeze every thing in your cooler and like PopBeavers says...make the plastic brittle.

Paul_Heuvelhorst
09-22-2007, 12:05 PM
Get an isolator or a relay. Set it and forget it. Just keep the TM plugged into the TV at all times.

Just a couple of additional comments to what others have offered.

If you are towing with a Ford product, factory equipped with the "tow package" your vehicle already has the vehicle battery isolated from the trailer battery. That makes unplugging unnecessary. If you are towing with another make vehicle, that doesn't have an isolator, buy one and install it (simple 3-wire connection). Here is an example of what to buy (www.campingworld.com/browse/products/index.cfm?prodID=1869&src=SRQB). You can buy such products at Kragen, Pep Boys, NAPA, etc.

Secondly, the fridge, when operating on 12DVC draws about 10 amps. That means 10 amps-per-hour. So, if your TM battery (deep cycle RV/marine type) is fully charged, it will take several hours (8 or more) to deplete the battery. If you don't have an isolator on your tow vehicle, then your trailer battery and vehicle battery are connected in parallel, and while the discharge rate is still the same (10 amps), you have twice the battery capacity, so the impact to both batteries is 1/2 of what it is on a single battery.

I am a strong advocate of the isolator solution. I prefer the diode type rather than a relay, but that is personal preference. Either type will do the job correctly.

I have been towing with Ford vehicles for 15 years, so it is a feature built-in to my vehicles. However, one of our sons bought a tent trailer last year and tows it with their Mercury Villager. I personally installed the 7-wire Bargman connector, a battery isolator, and the 10 gauge wire from the isolator to the Bargman connector so their trailer battery would charge while the vehicle was running without any impact on the car battery. It took me about 2.5 hours to complete the project... and I'm over 65, with some background in electronics! ;-)

lnussbau
09-23-2007, 05:45 AM
and while the discharge rate is still the same (10 amps), you have twice the battery capacity, so the impact to both batteries is 1/2 of what it is on a single battery.

True, in terms of current draw, but not necessarily in terms of capacity remaining, since the trailer batteries usually have greater capacity to start with, especially when, like mine, there are two large 6 volt batteries wired in series (so it's a very large 12 volt battery, in effect). So it's likely that the TV battery will run down sooner, though once it drops below 12 volts (not good) there would be some charging effect from the trailer battery.

But I'd certainly agree that an hour or two for lunch, won't cause the trailer battery to run down, and that an isolator is very desirable. I might note that if, like me, you often have an electric cooler in the TV, that drain needs to be considered, as well.

Incidentally, I've found that, so long as the frig and/or the cooler is not opened, an hour or two without power won't cause serious warming of your food, though I'd not want to go much beyond that -- certainly not overnight at a motel, for example.

FightinIrish
10-10-2007, 05:10 AM
Thanks to all. My tow vehicle is an 07 Toyota FJ Cruiser. Ill check into whether it has an isolator or not.