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How to charge li-ion batteries

Discussion in 'General Electronics Discussion' started by the13bats, Aug 1, 2018.

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  1. the13bats


    Aug 11, 2015
    I was putzing around with my large scale rc buggy and in need of new receiver batteries,

    So i busted into an old laptop battery pack and its got a total of 6 cells they are arranged both in series and parallel, but if i ran 4 in series and parallel i get 7.4 volts, great for my receiver,

    Now the snag, i havent a clue how to charge pirated li-ion batteries like this, so please clue me in...

    Many thanks,
  2. Bluejets


    Oct 5, 2014
    You must use a charger dedicated to the particular cell type to begin with.
    These batteries have tight tolerances on maximum charge/discharge level AND method of charging.
    Get it wrong and at some time you WILL end up with smoke and fire.
    I assume your hack does not include a battery protection circuit ....eeekkkkk !!!!
    R/c suppliers or Ebay etc. have various ones differing in quality, charge rates and monitoring and equally, price.
    If only an r/c buggy, you might want to go for the old square or flat 4 cell NiMh battery.
    Some can be had for as little as $8-$9 off Hobbyking, a bit more with delivery. Stll probably cheaper (and safer) than your hack battery. :eek:
  3. the13bats


    Aug 11, 2015
    Okay so not as simple as the old phone batteries l use for other stuff,
    Bought a 99 cent charger off ebay, plugs into phone charger cord, has light that goes out when battery is done...never got hot.
  4. dave9


    Mar 5, 2017
    I don't understand the question. Laptop batteries are typically 18650 cells. You can buy chargers capable of charging those on Amazon, a dozen models at least.

    If you want to charge them in the receiver as a series of cells then you need a hobby charger capable of a series of cells, a balancing charger.

    HOWEVER, something is very wrong here. It might just be the way you described your series and parallel battery pack. You wrote if you ran 4 in series ("and parallel" can't be used to describe this so I know what you're saying but you wrote it wrong), because 4 in series is 14.4V, so you must have meant 2 in series and another 2 series in parallel.

    Now I question what you are doing. What is the original battery config of the controller or receiver, which is it? The controller is what you hold in your hand., The receiver is in the R/C vehicle and also powers the motors???

    Either way, if you are willing to pull out the 18650 cells and charge them individually then get a charger on Amazon (or elsewhere) that can charge 18650 cells. It does not matter that they are "pirated", except that they might be far below their original rated capacity at this point, and if the R/C vehicle was supposed to use protected cells, laptop cells typically do not have per-cell protection, instead depending on a battery board in the pack to provide that.

    It won't be a problem in a charger designed for 18650 cells but might be in the R/C vehicle if it doesn't have its own low voltage discharge protection circuit. If it doesn't then you need to add one.

    If you meant that you have 2 series of 2 parallel 18650 cells in the hand-held controller, I am surprised it would fit that many cells and am also doubtful that it needs to fit that many because the controller runs through batteries (is much lower current) much slower than the pack in the vehicle does. If it were an R/C plane with extreme range so it needed higher transmission power, maybe then.

    Ultimately this is another case where you didn't describe what you are doing in fine enough detail. Remember, you see and know what you are doing but we, only know what you tell us.
    Last edited: Aug 1, 2018
  5. the13bats


    Aug 11, 2015
    Dave, yes, i worded that thinking 4 batteries in total,
    Two in series two in parallel,

    I also said receiver, but didnt go into details as it wasnt the point,
    A receiver runs less voltage than a transmitter,
    And no these odd sized cells would not fit in any transmitter i owned,
    No worries,
    Ive been messing with rc well over 40 years, i even worked in the industry, sales and R&D as a side line to my actual unrelated business, i did stop working in it several years back, and only bother keeping up with what i have interest in,
    Since im old school i find electric powered models boring, but thats the trend and where the hobby is today,

    I have collected a lot of stuff over the years but i mostly like large scale gasoline,
    So the only low voltage situation i care about is handled by a device that grounds the engine and kills it if the voltage drops to a set level, running lights flash to warn before that too,
    30 years ago we just ran redundant systems in models that could kill if they ran wild....or took the risk, scary.

    I likely shouldnt have mentioned what i desired to use the batteries for, it just clouded things , and i did hit ebay, and sure enough they offer a charger that is for the voltage i need, i think it was 4 bucks,
    Wont over charge, etc, so im good,

    I guess i should have hit ebay first but slipped my mind,
    So im pretty much good here,

    Thanks all
  6. Bluejets


    Oct 5, 2014
    Watch that receiver voltage. Newer type might handle it but older units won't like anything over 6v. Even then, Futaba for example can get over sensitive over 5v.
  7. the13bats


    Aug 11, 2015
    Thanks for the tip,

    Ive ran more futabas that i can count at 6v as they are made to do never an issue,, perhaps you meant 6v or had a picky defective receiver,

    I didnt actyally say what voltage i would give my receiver just what the battery had,

    Like i said after doing this rc thing well over 40 years, including working in R&D for companies,
    Ive tackled many voltage issues,

    i should have left what i wanted to use the batteries for out of this, as it became the unwanted focus
  8. Bluejets


    Oct 5, 2014
    No, it was a real problem and the move away from 6v was a direct Futaba recommendation and it fixed the problem.
    I don' t make statements like this willy nilly.
  9. the13bats


    Aug 11, 2015
    I never said you were willy anything and thanked you for your tip,

    I personally didnt see it in 100s of receivers in countless hours of use over 30 plus years but like i said this isnt the topic of my thread,

    So please bring any more rx talk to private,
  10. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    Jan 21, 2010
    Back to your original question...

    The cells you have can easily explode or catch fire if overcharged. They can also be damaged if they are discharged too far.

    The battery pack you took the cells from would have had a controller in it to prevent either of these things from happening.

    If you charge the cells individually and discharge them as a pack you must be careful to stop discharging as soon as any cell drops under a certain voltage, say 3V. Depending on how you have wired your batteries, you may need to monitor 2, or all 4 cells.
  11. the13bats


    Aug 11, 2015
    Thank you steve, you gave me the info i needed,
    I consider this thread done.
    Again thanks
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