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Thread: DIY Li-Ion Battery pack

  1. #1
    Unenlightened
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    Help DIY Li-Ion Battery pack

    Hi Guys,

    This site really rocks. I've found lots of useful information already. I'm new here, so forgive me if I'm saying crap.

    I'm about to try buy some 18650 batteries (http://www.dealextreme.com/details.dx/sku.5776) and was wondering if there was a way to connect them together in parralel to increase capacity?

    Is this dangerous?
    Do you know some good and easy battery holders that could do (better if can be found on DealExtreme)?
    Ultimately, I would like to use those to drive 2 or 3 seoul SSC-P4 LEDs. Possibliy using this regulator: http://www.dealextreme.com/details.dx/sku.6190
    Any advice?

    I'm also looking for good heatsinks, but heaven't found good ones yet on DX. Have to go to local store and look-out for copper or such parts, looks like it's the best option.

    thanks for your help

  2. #2
    Flashaholic* VanIsleDSM's Avatar
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    Default Re: DIY Li-Ion Battery pack

    Putting the batteries in series will increase the voltage, capacity will remain the same.

    Putting them in parallel the capacity will be increased, and both are safe to do for running a light.. charging is a different story though.

  3. #3
    Unenlightened
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    Default Re: DIY Li-Ion Battery pack

    Thanks for your reply.
    Charging should not be a problem if I can remove the batteries from the battery holder. this is what I'm looking for a battery holder that would fit the batteries in parallel. Do you know where I can find such battery holders?

    I was planning on charging using this: http://www.dealextreme.com/details.dx/sku.1251

    Also, anyone can help on the other questions?
    thanks

  4. #4
    Flashaholic
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    Default Re: DIY Li-Ion Battery pack

    If you're only going to charge 18650's, take a look at these chargers:

    http://www.dealextreme.com/details.dx/sku.6105
    http://www.dealextreme.com/details.dx/sku.5837

    They're similar, just a single and two cell version.

    I have two of the single cell ones, both won't charge beyond 4.2V and with a charge current of 1A per channel, they're a lot faster than the WF-139.

  5. #5

    Default Re: DIY Li-Ion Battery pack

    Disclaimer - I've never done any of this...hopefully someone with more experience/knowledge can tell you how to do it safely.

    Li-ion plus high heat, like from a soldering iron, is potentially very bad. There are the ones with tabs for making packs. Make sure you have a good answer before you learn any lessons the hard way.

    Depending on form factor you are looking to fit your project, computer heat sinks might fit your needs and be relatively easy to get your hands on.

  6. #6
    *Flashaholic* LuxLuthor's Avatar
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    Default Re: DIY Li-Ion Battery pack

    Do yourself a favor and take some time to do some reading about this. Do your research on buying cheap Chinese Lithium batteries. There are practical and safety issues, but I don't have time to give detailed response. Do not solder Lithium Cobalt cells. Quality and reputation is very important when dealing with Lithium cells and chargers.

  7. #7
    Unenlightened
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    Default Re: DIY Li-Ion Battery pack

    Even when using these batteries as standalone, you're saying there are safety issues? I thought they were protected (the ones I specifically mentioneed in the thread above), and that the chargers were limiting battery voltage too. Did I get it wrong?

  8. #8
    *Flashaholic* LuxLuthor's Avatar
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    Default Re: DIY Li-Ion Battery pack

    It is a huge step up to use a Lithium cobalt Ion cell WITH a protection PCB, so that is a good step, but as these photo's show, there are still variations in the quality of the PCB & components used.

    There are also some great threads that have been written on Li-Ions in general, such as this one started by Newbie.

    The main concern that some of us are trying to (diplomatically) get across is to both learn about the proper use of Li-Ions (which you may already know about--but a surprising number of Li-Ion users do not), but also to appreciate the quality control/manufacturing issues with various brands.

    When you get into cheap Chinese technology products, some of them are good and some are downright dangerous. Most of these Chinese companies are ripping off patented quality products, and reproducing them as cheaply as possible. Most have no international liability/reputation concerns, so they have little motivation to go the extra mile to ensure a basic standard is followed, or even that their products are safe.

    Good examples of safety design issues are the cheap Chinese chargers that unlike the more expensive Hong Kong manufactured Pila IBC, do not terminate the charging at 4.2V, but many Li-Ion users have no idea what can go wrong with overcharging them, or even if a charger they are looking at does terminate properly. They focus instead on some irrelevant issue such as the charging rate, like that makes it a better charger for Li-Ions.

    The next issue to examine is the DX link to your trustfire 18650 cells gives the detailed technical information of:
    - High rate discharge, no "memory effect"
    - Short circuit, over-charge and discharge protection
    well, what does that mean exactly? How high of a rate of discharge should one assume is safe with these cells over a sustained duration? What are the over-charge and discharge protections set at? How have their PCB & protection components been tested? Who tested and verified them? What type of quality does the underlying cell have? How reliable is their manufacturing process? Do they have any quality control? Do they give a rat's arse if anything goes wrong?

    Since you are going to rely on the PCB protection circuit as your proper cell management strategy, don't you think it would be wise to find out the details and reputation of the components of the cells? This example from Norm was clearly his fault but it shows something that really happened from a supposedly "smart" charger....that wasn't really very smart or safety oriented. Another video of a forced laptop fire induced from intentional overcharging.

    Will a Trustfire brand cell with unknown quality of protection PCB/components give adequate protection? If you are willing to gamble, it may turn out fine....but I want something that has a reputation and quality track record. Has AW's cells been 100% perfect? No. I returned a batch 1-2 years ago that had problems...and I got detailed feedback on how this manufacturing defect happened, and the improved QA afterwards from AW, since his repuation as a seller is at stake. You don't have that reassurance or reputation from Trustfire/Ultrafire/Random-Fire.

    Sorry for this being a little bit "preaching," but I only began to learn about the detailed risks about Lithium Cobalt batteries just over a year ago...and I know these issues need to be stated freshly for new users who are not aware yet.

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