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Solid state charger

Discussion in 'Electronic Design' started by Inovation, May 2, 2007.

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  1. Inovation

    Inovation Guest

    Hi, I am working on a project using a solid state charger to charge a
    battery, but it breaks down
    with the battery load and won't put out. It works fine off the
    battery. This is a 12v system and the chargers are 1amp chargers. I
    have one type that works, but a couple of different ones that won't.
    Do I need a load resistor to fool the charging circuit? The batteries
    are only pulled down to 7.2 volts, but they won't work on a new
    battery either. What do I need to do?
    Thank you,
    TC
     
  2. Tam/WB2TT

    Tam/WB2TT Guest

    What type of batteries? Are the chargers meant for charging these?

    Tam
     
  3. EdV

    EdV Guest

    Some battery chargers "fold back" when they source too high a
    current. Weird that the charger doesn't charge a new battery. Are
    you sure the new batteries aren't dead?

    Send more info on batteries and chargers.
     
  4. Inovation

    Inovation Guest

    Yes, these are new batteries. They are Rechargable sealed lead-Acid
    18Ah batteries. One of the chargers is a DVE switching adapter Model
    DSA 30w Output 12v 2amp. Thanks
     
  5. Inovation

    Inovation Guest

    Can I externally use a resistor to keep the charger from " folding
    back?"
     
  6. First problem. The charging voltage for a 12v lead acid cell, needs to be
    well above 12v. It'll depend on the actual cell structure of the battery,
    but typically 13.8v. A 12v supply, will _not_ charge a '12v' battery.
    Second problem. Your batteries are hellishly over discharged, if they are
    'pulled down to 7.2v'. Normally discharge should not go below about 10v,
    or you risk destroying the cells.
    You need a voltage regulated supply, able to deliver 13.8v (check with the
    battery manufacturer for the right figure), which is then current limited
    to deliver the required charging current. Ideally, the system should have
    a two stage voltage level, turning up the voltage if the cell is bdly
    discharged, and then turing it down when the battery approaches full
    charge (to avoid overcharging the battery). Several manufacturers do
    control IC's designed to implement such a charger, but you are looking at
    something _much_ more complex than what it sounds like you have...

    Best Wishes
     
  7. Tam/WB2TT

    Tam/WB2TT Guest

    Try a 10 Ohm 10 W resistor in series with the charger. That should prevent
    foldback. The charger should be putting out at least 14 V on its end. If
    the battery is down to 7.2V, its gone, like somebody said.

    Tam
     
  8. True but the OP did say it was a 12V charger (not PS) and as long as
    it's meant for lead acid and not some other chemistry then a 12V charger
    will provide an appropriate output voltage. However sealed lead acids
    require slightly different charging than flooded.
    Now there's a possible problem. A good charger will refuse to start if
    the battery voltage is too low. Amoung other things to keep from
    charging a 6V battery with a 12V charger and 7.2V sounds more like a 6V
    battery than a 12V battery.

    Robert
     
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