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charging 2 independent batteries - solar

Discussion in 'Power Electronics' started by morphingstar, Nov 21, 2012.

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  1. morphingstar

    morphingstar

    56
    1
    Mar 1, 2012
    Up to recently I had 2 solar panels float-charging 2 independent batteries - until the panels got stolen. The charge capacity was not good enough, so I want to find a better solution. Searching for panels that would deliver 250 - 500ma (2 - 3 times more than float charge) I found spec's / price relations that make me think of using one panel at 500, feeding both batteries.

    Presumptions:
    12 vdc 600 amp 40ah batteries are unequally charged.
    Feed lines must be isolated using one diode per battery, consuming 0.5 - 1 vdc
    Loadfree panel vdc might be about 20+.
    Loaded voltage might be 14-15 vdc, excluding the isolating diode voltage.
    Lowest battery voltage without voltage drop in wires might be12.
    In this circuit the lower charged battery might get more current than the other, = good.
    I do not intend to add a control device for cost reasons.
    The negative pole of the batteries are connected together.

    The "float charge" situation happens only when the sun rays are perpendicular to the fixed panel, a few hours per cloudless day. This is why 2 -3 times more current is required.

    Do you see any "pot holes" on the way of creating this system? I can not yet, I have never done this particular "one panel / 2 batteries" circuitry.

    Thanks for checking.
     
  2. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,451
    2,809
    Jan 21, 2010
    The main issue is that the battery with the lowest voltage will hog all the current.

    This will be an issue if one battery loses a cell, it will allow the other battery to go flat.
     
  3. morphingstar

    morphingstar

    56
    1
    Mar 1, 2012
    1 solar charging 2batteries

    Correct, you got a point, thanks. If a battery loses a cell, its voltage will drop by that cell under load conditions, or the cell prevents current to flow. Most likely the bad battery will be detected by the owner / user, whether in good time I can not predict.

    I presume this problem has been solved somewhere with some circuitry. Where could I find it?

    Diagram attached.
     

    Attached Files:

  4. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,451
    2,809
    Jan 21, 2010
    The normal solution is to use a proper charger and (most importantly) to keep your batteries in good condition.

    If these are flooded cells, then they will tolerate overcharge much better than gel cells.
     
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