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sealed lead acid battery charger

Discussion in 'Misc Electronics' started by [email protected], Oct 30, 2005.

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  1. Guest

    Hiya,

    I wish to design a system that will be connected to the mains and will
    charge a battery (small 12v battery) that will continue to supply power
    even if the mains goes off (A.K.A. - powercut)

    So i figure I can just use a simple charger
    (http://www.durhambats.org.uk/batlight.htm), that constantly charges
    the battery. But my question is, how effective is this, would it damage
    the battery, and how would I then take my power off the battery to my
    electronics, Becuase if i draw off say 5v through a regulator would I
    need to have increase the voltage that I charge my battery at to keep
    it constantly charged?

    Yours Gratefully

    David
     
  2. CWatters

    CWatters Guest

    Use a charger that has a Float/Full switch. The float setting is designed
    for permanant charging (eg months). On the float setting the voltage is
    reduced to around 13.5V to prevent the battery "boiling" and loosing
    electrolyte. On the float setting all you need do is check the fluid levels
    every few months.

    That article you linked to mentions this briefly... It says....

    "Battery manufacturers recommend charging at a charge voltage of 13.5 -
    13.8V for standby, and 14.4 v - 15v for cyclic (charging and discharging) -
    but if using the latter, which gives a faster charge, you must turn it off
    when fully charged. I use the 13.8V option, and leave my battery charging
    until I need it"
     
  3. default

    default Guest

    If your "small" battery is matched to the charger (can't overheat the
    battery by trying to charge too fast) you should be goood to go.

    Your regulator has nothing to do with the charger. You'll get 5V as
    long as the battery has 9 volts to supply (or 6 volts with a low drop
    out regulator)

    Your regulator provides 5 volts to your electronics. Your battery is
    out ther doing its best to maintain 12+ volts. You don't need to
    worry about the charge - the battery charger takes care of that part.

    you do have a battery charger?

    We use things like "battery disconnect" circuits that disconnect the
    battery, lest it be discharged too low and destroyed . . .(applies to
    lead-acid batteries - but not capacitors and most NiMH, some NiCads,
    etc..)

    Many batteries can be damaged by discharging them "too low"
     
  4. CWatters

    CWatters Guest

    No. Lead Acid batteries need a constant voltage charger. Just leave the
    float charger connected. It will automatically supply the extra _current_
    needed to compensate for the current drawn by your circuit. However the
    charger must be rated for that current. eg If you want to draw 7A from the
    battery continuously you need a charger that can supply at least say 8A.
    That's 7A to power your circuit and 1A to charge the battery. I have a cheap
    float charger that can supply about 3A no problem.
     
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