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  1. #1
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    Jun 2010

    Building my own 18650 packs?

    I have a couple of lights that are powered by the usual multi-cell lithium packs. At the moment, I am using the packs that came with the lights, but would like to assemble my own using some 18650 cells I've scavenged from dead laptop batteries. I'm well aware of the safety concerns with lithium cells, and am hoping that folks here can comment on my plan, and perhaps offer advice on improving what I'm doing (I'm also asking the guys over at candlepowerforums).

    I'm going to be charging the cells individually, profiling them for capacity , and grouping the cells according to their capacity. Note that I won't be welding the cells together, so I will continually have to remove and recharge the cells, as well as occasionally re-profiling them. And yes, the charging will be supervised and done inside a metal box, well away from anything flammable.

    I'm planning to use the MPD battery holders from Digikey (BK-18650-PC4). I haven't settled on a protection circuit yet though (my lights show the charge level, so I *could* skip the protection and just pay attention to the indicator).

    How does all of that sound?

    And yes, it's a lot more effort than buying a pre-built pack, but I enjoy this sort of thing, and would like to make use of the 18650s I have. My brother, on the other hand, would rather buy a pre-built solution, so if anyone has recommendations on a decent supplier, please let me know!

  2. #2
    mtbr member
    Reputation: Fourtrax's Avatar
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    Mar 2013
    I just built up some 14.8V battery packs using the same holders.
    See this thread: 35mm Easy2Led build

    I built one using reclaimed laptop batteries and one using new NCR18650B from Fasttech.
    With the flat top batteries, I had to add some solder to the contact springs since the batteries were too short.
    If you buy protected batteries, they fit without adding solder.
    If you are going to use a protection circuit, I would use a balance plug and balance charger so you don't have to remove the cells to charge and can then seal up the batteries.

    I've got the 2 protected batteries wired in parallel in the same holder for a 3.7V light and a super glued inner tube to put them in for water proofing. It is a pain taking them in and out to charge every time.

  3. #3
    mtbr member
    Join Date
    Apr 2010
    Laptop battery packs are usually disposed, because they no longer hold charge, meaning that there is at least one bad cell in that pack. Other cells are tired too since they'we been through al lot cycles. The won't last long either. But they are usually free. Since you'll be using holders for those cells, the cells will always be balance, but that doesn't mean they will discharge equally. For so much effort I'd be buying some decent quallity cells. Regarding holders. They usually come with premounted wires wich are way too thin to be usable. You wil need to rewire those packs anyway, so make sure you use thick enough wires since there'll be some current running through them. You might also run into a problem while rewiring those holders because they are made of crappy plastic which melts really quick when soldering new connections. Thinner wires cause more ressistance ruslting in bigger power loses. Protected cells might not fit in all holders so make sure they do in those you'll purchase, or the holders will crack. Prebuilt packs are always an easyer solution, but it might get expensive if decent cells and protection circuitry are used.

    If you ask me, get a hobby charger, decent cells and protection, quality wires and connectors, some shrink wrap and liquid rubber and you're good to go.

  4. #4
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    Reputation: mattthemuppet's Avatar
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    Jul 2004
    sounds like a fine plan to me. You won't get the runtime of the latest and greatest cells, but as long as the reclaimed cells hold a charge, have reasonable capacity and don't sag heavily under load you should be good. Charging them individually will help with mixing and matching cells, which is usually a no no in making packs (as they start diverging in charge status over time).

    I've torn down more packs than I can remember (60+?) and the cells are either all tired or one to 2 parallel banks are duff (0-1V), with the other cells being pretty much fine. I've made a bunch of different batteries with them (including an 18V 5S2P li-po pack that runs my power tools) and they're all holding up.

    Besides, even if you go down the reclaimed battery route now, with that set up you can always buy some higher capacity cells in the future, so you get the best of both worlds.

  5. #5
    mtbr member
    Reputation: Fourtrax's Avatar
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    Mar 2013
    I did not have any issues soldering with those Digikey holders. Both in adding solder to the tabs, soldering wires to the tabs as well as soldering two holders together (the tabs fit nicely with 2 holders back to back). Also did not have any problems soldering 12ga Cu wire between two contacts to run them in parallel. If you hold the solder gun right on the plastic it will melt easily, just don't do that.

    The datasheet rates them to 180deg C. Also self-extinguishing thermoplastic polyester so they won't burst into flames when you get them too hot.

    One warning, the little hole on the side that looks like it's made for a zip tie hold down (large red circle), don't try and cut this with a pair of dikes. I tried to cut it out so I had a clean path for the wire to go from one side to the other. When I cut it, the whole holder cracked almost all the way across. Of course this was after I already soldered the 2 holders together and soldered all the wires and tabs. I was able to fix it using some wire tie wrap so all was not lost. My second pack, I just drilled a hole where the small red circle is to pass the wire from one side to the other.

    Building my own 18650 packs?-capture.jpg

  6. #6
    mtbr member
    Join Date
    May 2005
    My experience with savage laptop batteries is this. If the pack was well used, 3 or 4 years old, and replaced due to short run time it was not worth the effort to pull apart as all cells were pretty low in capacity. One pack I got from a laptop that failed after about a year yielded 6 nice Sanyo cells in the 2600mA range. Another pack I got had died very early compared to what one would expect. That one had one series pair that were bad and four others in fine shape. Sony cells (I think) at 2400mA. All ten of them are better than any of my blue ultrafires that are a supposed 2600mA.

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