Li-on Battery Charging for Senior Design Project

Discussion in 'General Electronics Chat' started by Farvo702, Apr 6, 2009.

  1. Farvo702

    Thread Starter New Member

    Apr 6, 2009
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    Hi everyone, I'm kind of new to this forum, and I wanted to ask the all knowing populous some question. I'm building a small arm 9 pda like device, and I want to power it from a small lithium ion battery. I've asked a couple of questions about li-on stuff and decided I needed a battery management chip, cause the batteries could blow up :eek:. I chose the bq24071 from TI, but I need to test the chip, and the only package available is a qfn package. Can anyone tell me if there is something out there that I can breadboard, test with a battery (preferrably something like the ubp103450), and get a pcb done without breaking the bank, (under 50 bucks, just for the chip and everything, not the pcb board).

    Thank you for listening!

    P.S. I'm going to UNLV, I'm a senior in electrical engineering.
     
  2. Externet

    AAC Fanatic!

    Nov 29, 2005
    762
    57
    Hello Farvo.
    First let's make sure we are talking about aLi-ion battery or a cell.
    A [series] battery needs to have all its cells charged individually applying 4.100 VDC, at nearly any current.
    If you have a battery of several series cells, apply 4.100 VDC to each cell, simultaneously or one by one to recharge. Do not apply to the series battery the voltage sum that several Li-ion cells in series take. No mysteries.
    You can avoid management chips/circuitry this way as this is for test only.
    Miguel
     
  3. Farvo702

    Thread Starter New Member

    Apr 6, 2009
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    I can apply the 4.1 V since it is a single cell battery, however, I'm going to be implementing this in a finished sealed package, causing some problems, like overcharging, or overdraining, which I heard were really bad for li-on batteries. could I use a straight power management package, and put it in parallel with a charger circuit, so in case the charger begins overcharging the power management package will take away the load?
     
  4. Farvo702

    Thread Starter New Member

    Apr 6, 2009
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    ohhh and I forgot...

    Thank you for the response, I appreciate your help! :)
     
  5. Externet

    AAC Fanatic!

    Nov 29, 2005
    762
    57
    Hello.
    Applying regulated 4.100 volts directly to the cell will not overcharge it, but you can use a complex management IC if you want to.

    Do your tests, and if in a sealed package, make sure the cell does not get warm while charging/discharging. If paranoid, make it anywhere between 4.0 and 4.080 Volts.

    If it does go over 40C, reduce the charge current or if it does while discharging, use a larger ampacity cell (or two in parallel) Two+ in parallel can be handled as if it is a single cell for charging/discharging considerations.

    It could be:

    Steady +4.7V-------------|>|-----------L------------+Cell-----------GND

    The diode should be silicon to drop about 0.6V. Hand select to get 4.1000 V or fine tweak the supply to not exceed it.
    "L" is the node for your load, goes to the power switch
    Cell can be one or several in parallel.
    No need to worry if the charging supply is well voltage regulated, it will not overcharge that way.
    It is convenient to cease discharging when the cell reaches its rated 'discharge' voltage per manufacturer specifications.

    Miguel
     
    Last edited: Apr 7, 2009
  6. Farvo702

    Thread Starter New Member

    Apr 6, 2009
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    0
    Thank you!

    I'll get workin on the circuit. I appreciate the help!
     
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