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Battery pack charging

Discussion in 'Electronic Design' started by James Thompson, Sep 2, 2006.

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  1. I have been thinking of a design for series battery packs and the charging
    of them. What I envision is custom wiring of the pack (other then its
    series connection) with each cell having additional wire (positive and
    negative terminals) feeding to a charge controller circuit. The charge
    controller will then charge each cell independent of the pack and stop the
    charge current when that cell peaks. Also for each cell in the pack, place a
    reversed biased diode to limit and reverse charging to the diode drop
    voltage when the pack is discharging or even when each cell gets fully
    charged and the others are still charging. Has this scheme been tried or is
    in use now?
    All comments welcome. JTT
     
  2. Luhan

    Luhan Guest

    Currently (no pun), lithium ion rechargable cells have 'built in'
    controllers that prevent several problems: overcharging, overdischarge,
    rapid dischage, etc.

    I guess that the cost of making the type of charger you propose (which
    would work), has not been cost effective on a comercial basis. So, a
    'less than optimal' compromise is to just charge the whole stack of
    cells as a unit and replace them sooner.

    Luhan
     
  3. ISTR Micrel doing some battery ics, mainly lion protection(grr, down
    Clarence), but it was a few months ago. Try looking at/in the
    pro-video mob, they have sophisticated chargers, HDTV camcorders aint
    energy efficient, BHphoto maybe ?

    Probably not worth the effort unless you need the last mA/hour


    martin
     
  4. Multi tag charging is common in some laptops.
    Have a look at some, and they have about an 8 terminal strip on the
    battery. Two larger terminals at the ends, and a series of smaller ones
    between. This allows access to each cell voltage for the charging. Most
    are also smart enough to switch off the equipment if a cell gets too low,
    removing the need for the diodes.

    Best Wishes
     
  5. legg

    legg Guest

    I believe there's some emphasis on charge balancing using switched
    capacitor voltage equalization techniques, but not in commercial
    products.

    Regular series strings tend to balance during charge and float, due to
    the varying charge efficiency that occurs as full-to-overcharged
    conditions are approached.

    RL
     
  6. Thanks for all the replies. Nearly every pack I have had has died via 1 or
    2 cells going bad and I figured I would maybe rebuild packs like for my
    cordless drills to balance out the cells and extend there useful service. I
    was not really thinking about it in a commercial aspect, but for my own use
    to test out the idea.
     
  7. John

    John Guest

    Has this scheme been tried or is in use now?
    Check out the DIY Electronics forum (Aircraft - General section) at
    http://www.rcgroups.com/forums/index.php. They have several circuits
    for you to use and, I believe, circuit boards are available for some
    of the designs. This includes chargers and balancers.

    Check out the Batteries and Chargers forum too. Tons of info there.

    -- remove SPAMMENOT for e-mail responses --
     
  8. Mochuelo

    Mochuelo Guest

    That's one of my patents :p
     
  9. Barry Drodge

    Barry Drodge Guest

    HAve a look at
    http://members.shaw.ca/Botgoodies2/LithBatt/LithBatt.htm
    http://shdesigns.org/lionchg.html

    Barry
     
  10. A belated Yes/kinda, Check out the Hobby Sites. The switch to Li batteries
    has spurred battery pasks with IDC connectors for monitoring cell volatges
    and controllers.

    eg: http://www2.towerhobbies.com/cgi-bin/wti0093p?&C=ANC

    Cheers
     
  11. PeteS

    PeteS Guest

    TI makes some multicell chargers/monitors designed for charge balancing
    etc. by bringing out the pos/neg connections of each cell.

    Interestingly, they seem to use a technique I used a long time ago
    (well, 15 years ago) to clabrate the remaining charge state.

    Cheers

    PeteS
     
  12. Guest

    I think for such a design to really fly, you would need to both charge
    and discharge (i.e. use) the batteries in a manner where the cells are
    employed individually. You have now forced the design to have a charger
    per cell. Maybe the charger cicuit, which would be modeled around a
    DC/DC, can deliver an output current per cell that can then be mixed
    and feed to the load. Or the load, say a motor, has a winding for each
    battery.
     
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