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fredtowne's avatar
fredtowne
Explorer
Apr 10, 2014

12-volt refrigerator question

I have a 3-way refrigerator in my Chalet trailer. When I travel from one stop to another, I use the 12-volt option to keep the refrigerator cold along the way. It draws about 9 amps. Then I use either 120-volt or propane at the site. Sometimes, I will be camping in a location where there is no power, and the batteries will be discharged some from the stay. As I travel to my next stop, which may also have no power, I want my car's alternator to both keep the food cold and recharge the batteries. My alternator puts out more than 60 amps, but by the time the power reaches the 7-way plug to the trailer (while the refrigerator is running on 12-volt power), the voltage drop is such that little to no charging is occurring. It looks as though the wire to the plug from the alternator is about 10 awg. It seems like an 8 or 6 awg wire would probably handle the difference. Are the plugs able to handle 8 or 6 awg wire, and is this a good idea?

Thanks,
Fred Towne
Seeking Advice
  • JLTN_James's avatar
    JLTN_James
    Explorer
    Apr 14, 2014
    We rarely use the 12Vdc on the fridge, even when driving. It doesn't take long to discharge a new battery when stopped. We pre-cool the fridge on 120Vac and only put in food that's already cold. We can easily travel 8 hours in summer temperatures (80-95 degrees) without any problems. The propane flame almost always blows out when traveling so I don't bother with that.

    Remember that the electrical current has to have a good return path to the source (e.g. battery/alternator). Increasing size of the vehicle and trailer's charge line to 8AWG may help some, but unless you also increase the size of the return lines (misnamed "ground"), you won't get much benefit. Think of the wires like water hoses. You can upsize the supply to a fire hose but if the return is through a garden hose you're stuck with the garden hose capacity.
  • westend's avatar
    westend
    Explorer
    Apr 14, 2014
    How did you measure the alternator's output? I doubt very much that the output is that high.

    The biggest issue with using the vehicle's alternator to charge the trailer's batteries is that the alternator will only put out as much current as needed to keep the vehicle's battery charged and enough to maintain operating current. If the vehicle battery is fully charged, the alternator won't output much more than the operating current.

    Yes, increasing wire size will get more charge to the trailer but not that much more.
  • fredtowne's avatar
    fredtowne
    Explorer
    Apr 13, 2014
    I have made sure there is no corrosion, so that's not a problem. The alternator puts out 60 amps on idle, 100+ when driving. We limpet ovary ice cream, and the bars melt if we don't run the fridge. Also, we carry the propane on the back of the trailer, so running the fridge that way is not an option. Why have 12-volt if not to use it. My main thought was that an 8 wag wire should do the trick, and I wondered if others used that gauge on the connection.



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  • fredtowne's avatar
    fredtowne
    Explorer
    Apr 13, 2014
    We generally don't travel more than 4 hours. It just seems that it shouldn't be a big deal for my car to provide 20 amps or so back to the trailer while on the road.
  • Tothill's avatar
    Tothill
    Explorer
    Apr 11, 2014
    How long are your travel days? We run our class c fridge on gas when traveling, but it will stay cold (with extra ice packs) for several hours.

    The only time we use the 12 volt is when it is very hot and we have turned off the propane for a ferry crossing. Generally not more than 4 hours before we turn the gas back on.

    We can go five days on gas and batteries, no generator and an 80 w solar panel.
  • beemerphile1's avatar
    beemerphile1
    Explorer
    Apr 10, 2014
    Heavier wire will help but I run it on LPG almost exclusively now. I did have to make some modifications.

    For some reason many of the little 3-way refrigerators blow out while traveling, mine did. I bent some aluminum flashing to make a wind break to protect the flame. I also added a re-ignitor to help keep it lit.
  • ng2951's avatar
    ng2951
    Explorer
    Apr 10, 2014
    I am not sure just how long the power line is from the alternator to trailer. Those long lines have a lot of drop, and even when running shore power those fridges can have problems.

    If you can run on gas, I would. That was not possible on our old Trailmanor we had. We would have to hookup to shore power or the genset to refresh our batts at the end of the day.

    Part of the reason why our TM had that problem was because the battery was located in the rear of the trailer. That made those lines even longer. If your Chalet has the batts on the tongue that may be enough.

    The additional problem you have is the small size of your alternator. 60 amps just isn't that big. Also the 7-way plug can develop corrosion on it, especially the power connection.
  • mlts22's avatar
    mlts22
    Explorer
    Apr 10, 2014
    At best, the 12 volts will slightly maintain cooling, but in reality, the fridge is little more than an icebox. I'd definitely consider running it on propane, turning it off when at a gas station, or loading the freezer with hard-sided gel ice packs, and once those are solid, tossing 1-2 in the fridge part before a trip.

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