Newbie Looking for help with battery charging

Discussion in 'Power Electronics' started by Sr.Mayor, Jan 11, 2017.

  1. Sr.Mayor

    Thread Starter New Member

    Jan 11, 2017
    4
    0
    Hello everyone,
    I salvaged this battery pack from a bluetooth speaker and there is 5 cables coming out from it. I would like to know what is the white wire for and why there are 2 ground cables and 2 positives?
    How can I charge the battery? Can I use a 5v battery charging board using 2 of the cables only?

    Thanks in advance

    Kimi
    battery.jpg battery2.jpg
     
  2. MrSoftware

    Active Member

    Oct 29, 2013
    656
    182
    It's a 2 cell lithium battery. Most likely there are wires for charging each cell individually. See if you can figure out if any combination of 2 wires gives you more than 5v. If so, that means the batteries are most likely discharged in series, but charged independently. This is common with lithium batteries.

    To charge it safely, you will need a charger specifically for lithium batteries. The circuitry on top of the battery is likely for safety, but might also include charging. Can you identify any of the chips?
     
  3. Sr.Mayor

    Thread Starter New Member

    Jan 11, 2017
    4
    0
    Thanks for your reply. I dont know if the battery is dead or if is something wrong with the protection board, but no matter which wires I combine the voltage is 0. I can read 5.42v if I connect the B- from the board to any of the red wires, but nothing connecting the black ones.
    Any idea what this could be?
     
  4. bulrush

    Member

    Jan 1, 2017
    30
    1
    The lithium batteries may be completely discharged, and if they are, you cannot revive them, or it's very difficult, so you throw them away. Bigclive on Youtube did a video about this where he found a Pound Store power bank where the charging circuit actually slowly used up all the mah, and damaged the battery when the battery became empty. His videos are good for beginners and intermediate alike, but they are not tutorials, they are "let's take it apart and see how it works".
     
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  5. MrSoftware

    Active Member

    Oct 29, 2013
    656
    182
    If that circuit board has protection built in, then it would likely disconnect the batteries when the voltage gets too low. Draining lithium batteries completely can damage them, so protection circuitry often disconnects the batteries before they reach that point. That's a 2S battery (2 cells in series), so at 5.4v each cell is at 2.7v, which is low for lithium. Maybe you can save it by bypassing the circuitry to get some charge into the cells. Just read up and be sure you do it in a safe way.

    http://batteryuniversity.com/learn/article/premature_voltage_cut_off
     
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  6. Sr.Mayor

    Thread Starter New Member

    Jan 11, 2017
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    Thank you very much for your replies. I am going to charge the cells individually and try again.
     
  7. ian field

    Distinguished Member

    Oct 27, 2012
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    888
    Take care! - if you charge lithium cells more than a very specific terminal voltage; they can explode.

    Keep a bucket of sand handy - chucking water on a lithium fire makes it flare up worse!

    Lithium cells need a "topping charge" at the specified terminal voltage for a set period of time - they should not be left on float charge for longer than that.
     
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  8. MrSoftware

    Active Member

    Oct 29, 2013
    656
    182
    If it were me, I would just put a little charge into them and see if you can then get any readings from the wires. At that point maybe you can figure out how to charge through that board?
     
    Sr.Mayor likes this.
  9. Dodgydave

    AAC Fanatic!

    Jun 22, 2012
    5,791
    896
    What you have there is a battery monitor pcb, for charging and discharging..


    4.2V 2A 18650 Round PB.jpg
     
    Sr.Mayor likes this.
  10. ian field

    Distinguished Member

    Oct 27, 2012
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    Is that a generic part with some hope of finding datasheets?
     
  11. Sr.Mayor

    Thread Starter New Member

    Jan 11, 2017
    4
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    Don't you know if I could charge the batteries through that PCB? the main problem with mine its that there are 5 wires coming out of it.
    Thanks
     
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