Forum Discussion

vladio's avatar
vladio
Explorer
Aug 13, 2013

Charging the camper battery when driving

I'm trying to wrap my head around this one. We just finished up a weekend at a campground about 3 1/2 hours away. When we're pulling out, I switch the fridge over to 12v to keep it cold. I had the hitch installed at U-Haul and they wanted extra to run 12v back to the plug. The first camper we had didn't need power so i opted out. When we bought the bigger, newer pop up with all the bells and whistles I ran a heavy line off the positive of the battery along with installing a circuit breaker. All's hooked up right and I have power to the plug. After arriving at the campground Thursday, I attempted to raise the roof and could hear, even with the camper plugged in to the shore line and the power inverter doing its best to charge the battery, the battery was low. The roof made it about 3/4 way up and stopped. I used the manual crank and finished it up.

My question is shouldn't the van be powering/charging the camper when we're driving? It seems as though its not wired for this but I'm going to pull the camper info and look into this. I understand that it's risky as it could run down the van battery if we're stopped for a length of time but I can plan around that and use propane if we stop fr a lengthy period.

I look forwar to your input.

Thanks,
Joe
  • popeyemth's avatar
    popeyemth
    Explorer
    Aug 13, 2013
    Easy solution is to run the fridge on propane and you lose that high amp draw
    You need to run a battery cable sized wire to keep up with a fridge on 12 volts
  • spike99's avatar
    spike99
    Explorer
    Aug 13, 2013
    .

    All my RV/TTs have a trickle charger wire - from TV's Battery to RV's Battery. For this circuit, I use a thick 10 gauge wire (battery to battery) and use 40 Amp breaker near the TV's battery as well. Its a "trickle charger" and only works when its 7-pin connector is connected to the RV.

    For some TVs, they install an isolator unit. This module is installed within the TV's engine area and is active only when the TV's ignition key is turned ON. This isolator unit stops the TV's battery from over draining - if one parks the TV/RV combo (turns the key off) and forgets to pull the large 7-pin connector.

    If your TV to RV's "trickle charge" wire isn't working properly, suggest using a 12 Volt test probe and test is from end to end - with the TV's key turned ON (in case an isolator is used within your TV).

    As others suggested, run fridge on LP when traveling. If this sounds too scary, simply pack your fridge items in coolers. Then, load with block ice. This worked for me - when I towed < 3 hours.

    Hope this helps.
  • rexlion's avatar
    rexlion
    Explorer
    Aug 13, 2013
    The 12V draw of a 3-way fridge is really high. A setup like yours might do fine with a Danfoss compressor type DC-only fridge, or you might be able to get some joy by adding a couple hundred watts of solar panels to your roof. But really the easiest and most obvious solution is to leave it on LP while driving. Why are you turning it to 12V anyway? Are you afraid that the LP won't cool as much as DC? Just wondering.
  • MrWizard's avatar
    MrWizard
    Moderator
    Aug 13, 2013
    using about 20amps to power that fridge 12vdc heater coil

    if the charge line has too much voltage drop, then you might be only getting a few amps 4or 5 charge and the other 15 amps are coming from the popup battery

    run fridge on propane
    even while driving
  • time2roll's avatar
    time2roll
    Nomad
    Aug 13, 2013
    I agree that the high draw of the fridge on 12v is discharging the battery faster than the vehicle can charge.

    Although do check that the charge wire is working. Could be an open fuse or poor connection on the vehicle or trailer. With the vehicle running check the voltage on the trailer battery. As you connect to the running vehicle the trailer battery voltage should jump .5 to 1.0 volts.
  • vladio's avatar
    vladio
    Explorer
    Aug 13, 2013
    The fridge is at the rear of the camper and does not stay lit when traveling. I have no problem with running LP when running or sitting still but it blows out when on the road. My first pop up wouldn't stay lit either. I used duct tape to cover most of the removable panels to limit the airflow and it did work but 12v is just easier.

    As far as the draw, it's about 10 amps which is a good bit for a battery but my van has a towing package which includes a 185 amp alternator. This is def the way I want to go. We rarely stop for any period of time other than to get gas or let the 5 year old take a wiz along side the road. With the van running or even off for short period of time there plenty of power between the oversized Interstate deep-cycle in the rv and the 1000ca Interstate van battery.

    To me, it seems as though the camper's not wired to charge. Could this be? Is it not normal to have the rv wired to charge off the tow vehicle from the factory?
  • RAS43's avatar
    RAS43
    Explorer III
    Aug 13, 2013
    Or just run with fridge shut off 'till you get to your destination. Most fridges are insulated enough these days that 3-3.5 hours won't raise the temp. much at all. I run 6-7 hours some days and only gain a degree or two.
  • time2roll's avatar
    time2roll
    Nomad
    Aug 13, 2013
    It is normal for all to be wired to charge. Although verify that it is functioning. The long wire from one battery to the other will have some resistance and cause voltage to drop and limit the amps. #10 wire minimum for decent results. You may have 185 amps available but the voltage drop or an open circuit is probably hurting performance.
  • RLMiller's avatar
    RLMiller
    Explorer
    Aug 13, 2013
    I also agree that the 12 volt option for powering your frig may not be the best solution. Assuming the heater element in the frig requires 240 watts to cool the box, that translates to about 20 amps. It’s not likely any existing wiring to the back of the tow vehicle is sized adequately to carry 20 amps. Further assuming you use 60 feet of #10 wire for the 20 amp load, the voltage drop in the wire would be about 1.2 volts. The wiring connections could easily result in another 1 or 2 volts drop. So, if you run the wiring directly from the battery, or to a terminal near the battery with #10 wiring, and the battery was charging at 14 volts, you will only have about 11 volts at the trailer battery, or less if the battery is discharged and drawing even more current. A diode would result in another .6 volts drop, so a relay that cut in the line to the trailer would be a better choice than a diode, but the other voltgae drop is still present.
    To make a long story short, the idea of running the frig from the tow vehicle 12 volt system doesn’t bode well for success.

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