18650 batteries from an old laptop..

Discussion in 'Power Electronics' started by John O'C, May 17, 2017.

  1. John O'C

    Thread Starter Member

    Mar 22, 2017
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    As a newcomer to electronics, I have been given a couple of old laptops to play with.

    The only part so far that looks as though I may be able to rescue is a power supply. Having removed the PS, I have some questions, (See photos)

    1. I will be able to borrow an Imax B6AC charger/discharger to check the batteries (once I work out how to use it.). I suppose I will have to chop off the batteries and test individually?
    2. I assume the attached board is the charger/discharger? Seems a shame to have to throw it away.
    3. What are the silver components on the right - circled.
    4. What are these items (yellow boxes). I'm guessing some kind of sensors? _18650 Batteries_0004.JPG 18650 Batteries_0004 (2).jpg 18650 Batteries_0004.JPG
     
  2. MrAl

    AAC Fanatic!

    Jun 17, 2014
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    Hi,

    The 'sensors' look like thermal fuses. They blow open if they get too hot, but never close again. They are for extreme circumstances so that a fire does not occur.

    You could test each cell, but be aware that these kinds of cells age over time even when not used so they may not hold much charge. I guess it depends how good they where when first made in the factory. Some may work ok for a while. Depends on actual age too.
    Care must be taken in charging though to do it right or you could end up with a fire.
     
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  3. R!f@@

    AAC Fanatic!

    Apr 2, 2009
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    Yellow Square are temperature sensors.
    White Square are temperature fuses.

    It's not a charge/discharge PCB.
    It's the Balanced charger control PCB
     
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  4. John O'C

    Thread Starter Member

    Mar 22, 2017
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    Thanks

    They seem to be between 2.4/3.4 V , not having been charged for years.

    Are they usable?

    Thanks, I'm guessing it's not reusable (for a novice anyway.)
     
  5. R!f@@

    AAC Fanatic!

    Apr 2, 2009
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    Sensors can be used.

    Fuses can be used if they are not open.

    Can't say much abt the pcb to a n00b.

    PS. Never try to solder wires to the fuse. Heat from iron is enuf to open them. And if a cell is below 3.3V, you cannot get much out of it. You can charge them but it won't hold long.
     
  6. ian field

    AAC Fanatic!

    Oct 27, 2012
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    If you're going to mess with lithium cells; you need to be aware of the fire risk.

    End of charge terminal voltage is critical and not the same for all cells - Identify the cells and find the data sheet.

    Charging cells in series absolutely requires a balancing circuit - you can buy off the shelf units, which is likely to be much easier than re purposing the one in the laptop pack. You probably won't be able to find out the right charge current/voltage spec for the laptop PCB, sometimes they have sneaky tricks like a fuel gauge chip that declares the pack dead after a set number of charge cycles. Some have an ID chip that won't enable the battery unless it communicates with a laptop it recognises.
     
  7. MrAl

    AAC Fanatic!

    Jun 17, 2014
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    Hi,

    A cell with a voltage of 2.4v should be charged with a low current like 10ma or so until they come up to 3v or so.

    A cell with a voltage of 0v is considered bad to recharge due to problems inside the cell that could cause a short.

    You can actually solder the thermal fuses, but you need a good clip on heat sink and you must do it fast and you should only solder at the very end of the wire lead. That also means dont clip the leads short if you intend to solder them.
     
  8. ian field

    AAC Fanatic!

    Oct 27, 2012
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    The 18650 cells I salvage for my E-cigarette often come in dead flat - the last set I scrapped had served me nearly 3 years.

    A dead flat 14500 I rescued recently got hot on charge and settled at only 3.3V when it cooled - but I did use a charger intended for bigger things...............
     
  9. MrAl

    AAC Fanatic!

    Jun 17, 2014
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    Hi,

    Yes, that is an expert recommendation which is subject to vary due to the way the chemistry works over time and voltage. The expert opinion/recommendation is to avoid using them because there is the *possibility* of a problem that causes a short internally and that is viewed as an extra risk. So what this means in the long run is that we if we use 100 new cells we probably wont have any problem, but if we use 100 cells that had been dead down to 0v or near that just 1 of those cells might explode or catch fire. So it's viewed not as a definite occurrence but as an extra risk, an extra risk with something that is known to be dangerous when mistreated.
    I know someone who used one that was down to 0v or near that for a couple years, but that was it because they got rid of the phone and went to a new model. Never had a problem but i told them about the precautions.
    Most of the problems occur during charging, so if you charge in an isolated area or in a flameproof bucket you would probably be ok if anything went wrong. Have a chemical fire extinguisher on hand. I bought one a long time ago for something like $15 USD just in case one day something goes wrong.
    We know that one of these cells is going to catch fire for somebody this year, just dont want it to be me or you :)

    It's funny a gal i know had her gel pack puff up, not burn though recently.
     
  10. John O'C

    Thread Starter Member

    Mar 22, 2017
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    Thanks
    I tested for contiuity and they both "beeped", so I will assume they are OK
    Understandable :)
     
  11. John O'C

    Thread Starter Member

    Mar 22, 2017
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    Indeed I am.

    Yes, I intend to purchase soon.
     
  12. John O'C

    Thread Starter Member

    Mar 22, 2017
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    4
    OK
    Thanks for the good advice
     
  13. R!f@@

    AAC Fanatic!

    Apr 2, 2009
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    By the way...remember to test the fuse disconnected.
     
  14. ian field

    AAC Fanatic!

    Oct 27, 2012
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    The one I cooked went out the window just in case - lithium cells are the present day UXB.

    A Motorola phone battery from eBay inflated the first time I tried to charge it - luckily I found a safer supplier and the battery from there is still going over a year later.
     
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