Li-ion battery charger and supply to 5v load

Discussion in 'The Projects Forum' started by lwj5, Apr 22, 2012.

  1. lwj5

    Thread Starter New Member

    May 17, 2010
    13
    0
    Hello!

    I want to make a circuit where by when the 5v dc source is switched on it charges the 4 X 18650 li-ion batteries in parallel. The total internal resistance of the 4 batteries in parallel is 0.025Ohm and the batteries are pcb protected.

    And also while at it, it powers my load (a pocket router) rated at 5V, 1A input.

    The maximum my 5V source can produce is 2A.

    Here's the part where I just could figure out how to make it. How do I make it so that when the 5V source is present. The load (pocket router) is powered by the source and when the 5V source is switched off, it discharges from the batteries.

    credits to ifixit for the battery charger circuit from:
    http://forum.allaboutcircuits.com/showthread.php?t=35263&page=3

    Any help is appreciated! Thanks in advance
     
    Last edited: Apr 22, 2012
  2. evilclem

    Member

    Dec 20, 2011
    118
    16
    Diode from each to the load. The higher voltage source will power the load, this should be the 5V supply when it is present.
     
  3. lwj5

    Thread Starter New Member

    May 17, 2010
    13
    0
    Yup i understand that the higher voltage source will drive the load.

    Now the problem is that because the battery when fully charge will produce more then 5v through the step up circuit. Thus it will drive the load although the 5v dc source is plugged in. This will also cause the battery to never fully charge.
     
  4. evilclem

    Member

    Dec 20, 2011
    118
    16
    Perhaps connect a normally closed relay between the battery and the load.
     
  5. lwj5

    Thread Starter New Member

    May 17, 2010
    13
    0
    Thanks for the idea! I managed to do a rough edit of the circuit. The values are not on yet.

    but this is roughly how it will look like. Any1 care to comment?

    This circuit will be hooked up to the step up circuit in my first post
     
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