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Help with RV battery overcharge

Discussion in 'Off Topic' started by Traveler, Sep 5, 2016.

  1. Traveler

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    Greetings and please help.

    This is not a drone question or even an RC issue, but it is a battery issue.
    I boiled dry one of two batteries overnight in my fifth wheel.
    In this case my RV has a smart charger, aka (a wizard function) that automatically selects one of three operating modes: BOOST, NORMAL, STORAGE.
    Boost is 14.4 VDC @90 amps. This will rapid charge the battery to 90%, then it scales down from there.

    Here's the story. Getting the RV ready I had it plugged into my AC at home for three weeks. No problem during this time, batteries were just floating, remaining nice an cool the entire time. Then, ready to move out in the morning I hooked up the truck and the hitch plug, i.e., running lights break lights, etc., this is also has a 12VDC connection between the truck and fifth wheel and this is what I think caused my issue. The truck battery, with the long small gauge wire that goes between the truck and fifth wheel was much less voltage than would show on the full fifth wheel batteries, and this lower voltage triggered the wizard to boost mode, thus giving the already charged batteries 14.4 VDC @90 amps for the entire night. Next morning, boiled down battery.

    No pun intended, but does this theory hold water?

    Thanks for the replies!


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  2. 185EZ

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    #2 185EZ, Sep 5, 2016
    Last edited: Sep 18, 2016
  3. Traveler

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    Round connector, yes. Newish batteries, Same date, same purchase, Feb 2016.
    I will not have truck connect anymore when plugged into AC power.

    I think that it is what caused my overcharge. Agree?


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  4. 185EZ

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    #4 185EZ, Sep 5, 2016
    Last edited: Sep 18, 2016
  5. joet

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    That explanation doesn't make sense to me.

    Think of voltage as water pressure. Your battery already was at something around 12.8 volts, and the float charge would be about that as well. Any lower voltage from the truck would not allow current flow from the truck - in fact, absent a diode, would allow current flow towards the truck instead of away from. However, unless there was a significant parasitic voltage drop in the truck, this shouldn't have mattered for such a brief period.

    However, a lot depends on how the truck is wired in to the rig (direct to the battery, through the charge controller) and the controller itself.

    I may be wrong, but I don't think it's the truck.

    I suggest you go to RV.net and post on their forum - lots of very knowledgeable people there.
     
  6. 185EZ

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    #6 185EZ, Sep 5, 2016
    Last edited: Sep 18, 2016
  7. Traveler

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    Responding to a bit from all post, I have power at the plug with or without key on.

    I just am at a bit of a loss to otherwise explain it.
    My rig was on AC for three weeks and the batteries were fine, and I checked them often. Cool to the touch, voltage looked good, and the led on the converter was showing minimum charging.

    When I was getting ready to make it ready for an early morning departure here is how it went down.
    Electric raised the fifth wheel, (this uses batteries but the converted is still on at this point), connected the hitch and "round" pigtail, removed the AC, moved the truck and 5th wheel to the departure site (don't like to wake the neighbors at 4am), reconnected the AC for the frig, that it. So the only thing that changed in the three weeks was having the truck connected (hitch and pigtail).

    I have learned that when something fails or is not working right, what was different or changed.

    BTW, no battery isolated is used in this setup

    At this point it would be fair to say that the converter was in boost mode, but why remains the mystery.

    If I find out what happen I will share, but I very much appreciate replies and thought. Many smart people on this forum.

     
  8. WetDog

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    There SHOULD be blocking diodes in that circuit. Almost impossible not to have them unless the thing was jury rigged at some point. I don't think your theory quite works, but have you placed a multimeter on the circuit with the truck battery connected and not to see what the charger does? It is not unheard of for 'smart' chargers to get really stupid at times (see also the posts about DJI's 'smart' batteries). Battery charging and regulation is complex and not always done correctly even by manufacturers of said products.

    Also check your grounds. A differential ground could easily do this and may not get sensed by the charger. In the marine space, many, many problems are caused by wonky grounds.
     
    joet likes this.
  9. Traveler

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    It is all factory, 2011 Dodge Ram 3500 and 2011 Montana Fifth wheel. The cable for the RV look pristine and the ground is solid.

    I have to wait for Labor Day to pass to get new batteries then I will check as you suggest. Yes, I have a quality Fluke MM.

    The Truck is Diesel so it has two OEM batteries. I will separate them to day to ensure that one of them is not failing.

    Anyone know of any good RV forums?




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  10. 185EZ

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    #10 185EZ, Sep 5, 2016
    Last edited: Sep 18, 2016
  11. joet

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    Rv.net
     
  12. Traveler

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    Thank you all, I will consult with the RV forums.

    Appreciate your indulgence.



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  13. 185EZ

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    Did you ever find out what happened?
     
  14. RedHotPoker

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    What was the problem? Solved yet, or still looking for help?
    Yes, try the RV forum.

    RedHotPoker