Li-ion constant current method

Discussion in 'General Electronics Chat' started by billybobjoe, Mar 10, 2009.

  1. billybobjoe

    Thread Starter New Member

    Mar 10, 2009
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    Hi

    I am using this circuit attached which is fairly common method of getting a constant current of approx 1A to charge Li-ion batteries. however it just seems to be shorting out when i try attach the batteries. any idea why or how do i attach the batteries properly.

    (the attachment shows a load where my batteries should be. Resistor is the same - which should provide 1A)

    Or is there another way of getting a reliable constant current with Lm317?

    Thanks
     
  2. Audioguru

    New Member

    Dec 20, 2007
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    The input voltage must be at least 3.3V more than the output voltage and be able to supply 1A.
    The LM317 or LM117 will get too hot without a heatsink and will shut down.

    If a Lithium battery cell is charged higher than 4.2V then it will probably catch on fire.
    The circuit has nothing to limit the charging voltage.
     
  3. billybobjoe

    Thread Starter New Member

    Mar 10, 2009
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    i have a uC that will take care of switching off the charger when 4.2 volts are reached.

    what improvments should be made?
     
  4. Audioguru

    New Member

    Dec 20, 2007
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    Go online to The Battery University (look in Google). They have a graph that shows a lithium battery cell is about 70% fully charged when its voltage reaches 4.2V. The cell is fully charged much later when its current has dropped to about 3% of its recommended charging current.
     
  5. bertus

    Administrator

    Apr 5, 2008
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