Forum Discussion

oyly's avatar
oyly
Explorer
May 11, 2016

Fridge on 12V killing the batteries

Just came back from the shop where I got my new batteries after I toasted my first set. I got them replaced 5 months ago, and already they were performing poorly, even thought they were supposed to be real good quality deep-cycle batteries. So I just wanted them to put their battery tester on them to confirm my suspicions, and sure enough, they were no good. Very generously, they replaced them under warranty, even though I most likely damaged them with improper use. When talking to the staff, they asked me about my refridgerator. I said it runs three ways, on LP, 120V and 12V. They said I should never run it on 12V since this will damage the batteries. I tried to explain them that when the batteries are down, after driving the RV for a couple of hours, the batteries are fully charged, so even if the fridge pulls a lot of power, the alternator is more than powerful enough for both this and giving the batteries a good charge.

The still insisted it was not good to run the fridge on 12V. Now, I am an electrical engineer, and I cannot with my best imagination understand why it would be bad to run the fridge on 12V if the batteries are charged after a drive. The fridge should just lower the amount of current available to charge the batteries. And if that was a problem, then it should also be a problem to use a small charger to charge the batteries. I've never heard that it is bad for the batteries to be charged with a small current, only that it will take longer.

What do you think? Are the staff at this shop just superstitious, or do they have a point?
Class A
  • n7bsn's avatar
    n7bsn
    Explorer
    May 11, 2016
    You should only run the refer on 12V when the engine is running, the 12V heater sucks too many watts to run it when parked.

    Most 3-way's are wired to only run when the ignition is on

    Obviously your University didn't offer any classes on battery power, but then I guess mine didn't either, but the US-Navy took care of fixing that lack.
  • 2oldman's avatar
    2oldman
    Explorer II
    May 11, 2016
    I think you're fine. That's a 30a draw from your alternator.
  • oyly's avatar
    oyly
    Explorer
    May 11, 2016
    n7bsn wrote:
    You should only run the refer on 12V when the engine is running, the 12V heater sucks too many watts to run it when parked.

    Most 3-way's are wired to only run when the ignition is on

    Obviously your University didn't offer any classes on battery power, but then I guess mine didn't either, but the US-Navy took care of fixing that lack.


    Glad to see an expert took the time to answer! Why do you think it's obvious I didn't learn anything about batteries in uni? What did I get wrong?

    My fridge only runs on 12V when the engine is running.
  • MrWizard's avatar
    MrWizard
    Moderator
    May 11, 2016
    why were the batteries damaged if the fridge is only on 12v when driving

    what did you do to damage the batteries
    that you are NOT going to do anymore

    and you are sadly mistaken, that a few hours of driving will fully charge a depleted battery you might get back to 80 percent in a few hours... maybe
    but it could another 15 20 hrs in absorption mode to fully bring the specific gravity back to 100 percent charge
  • oyly's avatar
    oyly
    Explorer
    May 11, 2016
    MrWizard wrote:
    why were the batteries damaged if the fridge is only on 12v when driving

    what did you do to damage the batteries
    that you are NOT going to do anymore

    and you are sadly mistaken, that a few hours of driving will fully charge a depleted battery you might get back to 80 percent in a few hours... maybe
    but it could another 15 20 hrs in absorption mode to fully bring the specific gravity back to 100 percent charge


    I used the lights, carbon monoxide and LP sensors. I don't have power where I am at the moment, so I have to use the diesel generator to charge the batteries. I also have neighbors nearby, so running that generator for 15-20 hours is not an option.

    Excuse my wording about fully charging the batteries in two hours. I am not asking how to charge batteries. I was simply trying to make a point to the battery vendor that since the batteries have MORE charge after a drive and the fridge only draws 12V when the engine is running, then it can not be bad for the batteries: They are being charged, not drained.

    Clear enough?
  • jerseyjim's avatar
    jerseyjim
    Explorer
    May 11, 2016
    My OPINION : When not hooked up to shore power, use the PROPANE! End of problem.
  • oyly's avatar
    oyly
    Explorer
    May 11, 2016
    Judging from the answers to questions I didn't ask, I did not make myself clear enough.

    So, short and sweet:

    The battery vendor says leaving the fridge in automatic mode will ruin the batteries, so I should switch it to propane mode. Is he correct?
  • Teacher_s_Pet's avatar
    Teacher_s_Pet
    Explorer
    May 11, 2016
    If in automatic mode why wouldn't a 3 way, refrigerator switch to propane instead of 12 volt, is that an option? We have a 1200LRM Norcold 2-way in our Phaeton, just wondered.
  • Dale_Traveling's avatar
    Dale_Traveling
    Explorer II
    May 11, 2016
    Have you verify the chassis and house batteries are cross connecting when the engine is running? Easy check. When the engine is running and shore power disconnected you should see the same volts on both the chassis and house batteries. Something over 13VDC.

    What brand and capacity are the batteries? Not all batteries are equal. Something else to consider if one of the failed batteries had a bad cell that one cell will consume all the batteries in a bank.
  • horton333's avatar
    horton333
    Explorer
    May 11, 2016
    Clearly it is not the simple usage that is killing the battery. Either they are charged too much or too little, I'm assuming they were not simply defective. With the voltage drops from the connector etc. if you are powering a fridge you may not be charging the batteries much if at all, and I'd start looking there.
    How are you measuring that your battery is charged after a trip? What is the voltage at the battery when the fridge is on and being charged from the truck?
    How do you charge your batteries when in storage or when campping, or do you just disconnect them when not using the trailer? i.e. what is the state of charge when you begin your trips, have you measured it?
    There is the much less likely chance you are overcharging them with a defective charger or sonething, but they likely would have told you if you had boiled the battery.

About Motorhome Group

38,705 PostsLatest Activity: Jan 14, 2025