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Charge NiMH battery while still in circuit

Discussion in 'Electronic Design' started by [email protected], Jun 21, 2006.

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  1. Guest

    I'm working on a senior project and i am looking for the best way to
    charge a NiMH battery while it is still in use in the circuit.
    Basically when the robot senses a low battery condition it hunts out a
    docking station and docks. From there I'm a bit unsure on how to
    supply the charge to the battery and when to stop. Any suggestions
    would be great. Thanks.

    Dean
     
  2. On 21 Jun 2006 11:45:36 -0700, in sci.electronics.design
    Look at the data sheet for the MAX712/3 charger. Basically the 712/3
    has a low value current sense resistor feeding the battery, and it
    depends on which side of this resistor you take your load from, as to
    how the system measures the charge current.

    FWIW several people have commented that the trickle charge is somewhat
    high on this IC


    martin
     
  3. Nico Coesel

    Nico Coesel Guest

    NiMh batteries are best charged by sensing their temperature while
    charging. If the temperature rises more than 1 degree C, they are
    fully charged. Panasonic had some nice documents on how to charge NiMh
    cells.

    NiMh cells may not be the best choice for your robot. They have a
    nasty habit of dropping their output voltage very quickly when they
    are empty.
     
  4. Nico Coesel

    Nico Coesel Guest

    Oops! Forgot something important. This should read:
    NiMh batteries are best charged by sensing their temperature while
    charging. If the temperature rises more than 1 degree C PER MINUTE,
    they are fully charged.
     
  5. Luhan

    Luhan Guest

    Charging NiMH optimally can be very complex. I find it simpler to
    simply charge to a 'cutoff voltage'. This gets about 80-90% charge.

    http://members.cox.net/berniekm/unichg.html

    Good luck,
    Luhan
     
  6. ehsjr

    ehsjr Guest

    "Best" is undefined. "Best" can include consideration of
    what charging power is available, physical size, cost etc.
    In one scenario, you may need to charge very quickly, in
    another the robot may not be used for a very long time, so
    a trickle followed by a taper charge may be best.

    For an unspecified "best" use a trickle/taper.
    The "best" part of that is it won't cook your cells.
    "First, do no damage."

    Ed
     
  7. YD

    YD Guest

    Is that fuse really glowing? Looks a bit scary.

    - YD.
     
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