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Thread: 24 volt panels, 12 volt battery banks - what to do?

  1. #1
    Junior Member
    Join Date
    Jan 2012

    Unhappy 24 volt panels, 12 volt battery banks - what to do?

    24 volt panels, 12 volt battery banks - what to do? I got 24 volt panels at a 'stainless steal' price - but my existing system is 12 volts. Can anyone direct me to info on a charger that regulates 24 volt input but charges a 12 volt battery system? I seem to remember seeing such an animal, but I dont' remember when or where... and google gives me every answer but the one to the question I ask.

  2. #2
    Join Date
    Feb 2011
    Annapolis Md


    Use an MPPT controller such as the Morningstar Tristar charge controller. You could even put several in series for even higher voltage which = smaller wires from panels to controller if it is any distance or higher amperage.

    And welcome to SPT

  3. #3
    Junior Member
    Join Date
    Jan 2012

    Default clarification please and thank you for the welcome.

    My aim is to not lose any wattage that I don't have to that should be going the batteries. My best guess solution so far has been step down converters to 13.8 and then pipe them into the charge controller like they were 12 volt panels. Is my guesswork faulty, is there a better way, and what is the best way to not lose any wattage from the panels input and yet not have to reinvest in a new 24 volt controller, inverter etc.
    I have one such controller that you mentioned, the tristar moningstar controller. can i expect conflicts with the existing controllers if I follow your suggestion? the panels are unisolar 144 watt flex panels. They say 30 volts top output but unless my meter is lying to me (it might be republican) I am getting 44 volts!!! No load of course.
    ref your statement re several in series, please to specify controllers or panels?

  4. #4

  5. #5
    Join Date
    May 2009
    off grid retirement in Northern Calif


    Morningstar has 2 tristar controller lines, both LOOK the same, but one is MPPT, and other is PWM. You will have to check the model number. The MPPT model will efficiently down-convert 130VDC, to 12V for battery charging.

    You don't want to use a simple DC-DC 13.8V convertor, as that will not recharge your battery well in the few hours of sunlight. Most of the good 3 stage controllers, charge at 14.5V or so, and float at 13.
    Since the dawn of time it has been mankind's dream to blot out the sun.
    Montgomery Burns

    "Always listen to experts. They'll tell you what can't be done and why. Then do it."

    spreadsheet based voltage drop calculator:


    solar: http://tinyurl.com/LMR-Solar
    gen: http://tinyurl.com/LMR-Lister ,
    battery lugs http://tinyurl.com/LMR-BigLug
    Setting up batteries http://tinyurl.com/LMR-NiFe

    gear :
    Powerfab top of pole PV mount | 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 || || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

  6. #6
    Solar Fanatic
    Join Date
    Feb 2010


    Let's make it simple. Best efficiency you can obtain with:

    PWM is 67% or less, depends on how closely matched the panels are to the battery voltage.

    MPPT is 95% and higher.

    Nough Said
    MSEE, PE

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