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This charger seems dangerous

  • NightRider Wednesday, April 11, 2018 12:01 PM Reply

    I tried charging some 18650 Li-Ion cells and they overheated badly, too hot to touch.

    Also, the voltage applied is 4.26V, more than the allowed 4.2V.

    See attached picture.

    sku 173198 overcharging.jpg

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  • cyclist Moderator Wednesday, April 11, 2018 5:41 PM Reply

    4.26v is okay, its still just within the safe range.

    Was that the end voltage or charging voltage?

    You'll get a bit more capacity from the batteries at that and it shouldn't really cause any damage.

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  • gasbag11 Top 10 Forum Poster Wednesday, April 11, 2018 11:30 PM Reply

    I'm far from an expert on chargers etc., but I've read enough to know that if the cells are too hot to touch, there's something seriously wrong somewhere. 


    @sheepish

    @desolder

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  • sheepish Top 10 Forum Poster Thursday, April 12, 2018 6:29 AM Reply

    4.26v is okay, its still just within the safe range.


    What?


    You're talking about something which could explode if charged incorrectly. Let's give accurate advice.


    The cell is a Samsung ICR18650-26C, so it's (with an apostrophe) 4.2 ± 0.05 V (capital V; it's a unit based on someone's name). However, you can definitely expect charging at 4.25 V rather than 4.15 V to shorten the life of the cell. Maximum charging temperature should be 45 °C, which is cool enough to be able to touch continuously.

    http://www.meircell.co.il/files/Samsung%20ICR18650-26C.pdf

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  • desolder Top 10 Forum Poster Friday, April 13, 2018 8:37 AM Reply

    If your cells are getting hot while charging, then it's time to toss them out. Overheating is one of the first signs the cell is approaching its end of life.


    A slight overvoltage of 4.26V won't cause a cell to overheat. It's not the voltage that heats a cell, it's the current (times the internal resistance).


    Are you sure the cells are getting hot, and not the charger itself?

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    What are they trying to hide?

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    post edited by desolder on 4/13/2018 at 8:37 AM
  • matrix-neo Moderator Saturday, April 14, 2018 11:29 AM Reply

    maybe the charger doesn't have a thermal fuse or is placed incorrectly? either open up the charger to check or heat up a (dud) cell and see if charger cuts off current, and desolder is right, as a cell ages the internal resistance goes up which means it gets warmer during charging, unfortunately unlike Ni-Cd/Ni-Mh cells that can be revived, lithium cells can not, well i haven't found a proven way to reduce internal resistance

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  • NightRider Friday, April 20, 2018 1:14 PM Reply

    Thanks all for the responses. I am not sure that the 4.26V I measured is indeed the top limit, but I can now put another nail into this charger's coffin...checking charge current of cells still in the charger after the green lights come on, I can see that this charger is still pumping up to 50mA into the cells indefinitely and not shutting down, which AFAIK doesn't follow recommended Li-Ion charge termination algorithm.


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    post edited by NightRider on 4/20/2018 at 1:17 PM
  • sheepish Top 10 Forum Poster Friday, April 20, 2018 1:17 PM Reply

    Did it come with safety glasses?

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  • desolder Top 10 Forum Poster Saturday, April 21, 2018 1:39 AM Reply

    The green light may come on before the charge cycle is actually complete. It just indicates that the cell is "full enough". A 100% charge can take up to 3 hours, with that last 10% taking up half that time. Most consumers are are unwilling to wait 3 hours, so the green light may come on at the end of the "CC" phase when the terminal voltage reaches 4.2V (at that point the cell is only ~80% charged). Manufacturers recommend a termination time of 2.5 to 3 hours, and a termination current of 0.01 to 0.02C. IMO 50ma is still OK.


    Can you try measuring the current after 3 hours? If you can still measure current, then I would definitly be concerned.

    What's up with the scrubbed LED driver IC markings?
    What are they trying to hide?

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  • sheepish Top 10 Forum Poster Saturday, April 21, 2018 5:51 AM Reply

    My cellphone's green light comes on at 90% when charging, but what it calls 100% isn't necessarily quite full either. When being used after charging overnight it takes longer to depart 100% than it does to lose 1% anywhere else in a charge.


    50 mA at 4.26 V is not a great idea for a cell rated at 4.20 ± 0.05 V. Are they well-used repurposed laptop cells? Are you able to open the charger to have a look for a potentiometer you could adjust to dial back the voltage a bit?


    FWIW 8 milliannum (ma) is a little over 8 and 3/4 hours.

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