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'Mothballing' battery bank when out of service

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  • 'Mothballing' battery bank when out of service

    I have a remote off-grid cabin that is seasonal.
    By that I mean that I don't use it in the winter time. So it's all powered off (inverter off) in the off-season. I actually open the breaker to the inverter from the FLA battery bank.
    I always leave the cabin with the batteries fully charged.

    I thought that opening the breaker, the batteries were basically not connected to anything but on closer inspection, I realized that the charge controller was still connected.
    Because in the winter time, snow can sit on the panels for weeks at a time and the sun is very low in the sky... can be nothing coming from the panels and I was concerned that the charge controller would be drawing current from the batteries for extended periods of time with no recharge (probably very low leakage currents so maybe no big deal).

    This year when I realized this and was heading out the door, I tried disconnecting the breaker for the charge controller so there would be zero load on the batteries for the next 4 months....
    But on that sunny day, I got a fault from the charge controller which wasn't surprising because no batteries were connected. I wasn't sure I wanted to leave it in that fault state so I reclosed the breaker.
    I didn't want the batteries to get over charged or cycled with a bulk/absorb so I turned down both bulk/absorb to the Float voltage. Meaning the the charge controller would just do float 100% of the time (a trick I learned here).

    What do you guys think I should do? Open the charge controller breaker and not work about the fault? Leave on float and not worry about it?
    or ??

    Thanks much for your guys expertise.

    Riley

  • #2
    You should always disconnect the PV from the controller BEFORE disconnecting the battery.
    And , yes, charge controllers consume some power 24/7 as they maintain their settings and wait for the sunrise to wake up the panels.
    Powerfab top of pole PV mount (2) | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
    || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
    || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

    solar: http://tinyurl.com/LMR-Solar
    gen: http://tinyurl.com/LMR-Lister

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    • #3
      That makes sense Mike. I wonder if I have a breaker on the panel feed to the charge controller. I hope so....
      I think I might need to visit my cabin and change the setup before leaving it for too long.

      I just looked up the specs and the Conext-MPPT that I have is spec'd for 2.5 watts at night time. Not a lot but over a long period, it can add up.
      Last edited by Riley5781; 10-25-2021, 10:49 PM. Reason: specs on conext-mppt

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      • #4
        Update: I don't have a breaker on the input side of the charge controller so I can't disconnect the panels.
        On my MPPT controller, I see that it has a stand-by mode. Next time I will place into standby before opening the breaker and I think that will prevent the fault.
        Problem might be when the sun returns, does the controller remember that it's in standby mode. I might reset back to online if they don't save that setting in flash/NV.

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