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Thread: Round Battery Holder for 3 or 4 21700 Li-ion batteries, where to find?

  1. #1
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    Default Round Battery Holder for 3 or 4 21700 Li-ion batteries, where to find?

    Hello,

    I've looked but not finding exactly what I was hoping to find, I'm seeking a tubular battery holder for three or four 21700 5000 mAH Li-ion batteries physically arranged together in parallel (even better if for more than one battery in series), but not necessarily wired together, although that could work if I modified the wiring to straight series instead of what ever configuration the holder comes with such as parallel or series-parallel.

    Click image for larger version. 

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    If using the Nitecore NL2150HPR 21700 batteries in this configuration I could have three 5000 mAH 15 amp continuous current rated outputs for a total of 15 AH.

    Here's an example of what I'm looking to find, although these are for AA batteries, not the 21700 battery I want to use: https://www.joom.com/en/products/151...193-3038656925

    I want three or four strings of two to three batteries in series (not electrically paralleled together) but physically all nested together in a tube or handle for a large jumbo pointer to connect different devices to each string, so no need for electrically paralleled batteries. I have this type of pack from a Fenix TK75 flashlight for 18650 Li-ion batteries which are wired series-parallel to produce 8.4 VDC from four cells (Danger if paralleling unequal batteries!), but I really prefer the 21700 cells and do not want to electrically parallel them, if I can find a holder like the above joom.com example linked to.

    I did find this: Cell holders x3 21700 (e-bikestuff.com) - These may be the closest I can get for three strings of batteries in series, but still looking.

    Note: Paralleling Li-ion batteries is fine, but in my opinion they must be strapped and spot welded together to prevent a huge poof if accidentally paralleling a fully charged battery with a discharged one. Strapped paralleled batteries could work for my application, but I want to be able to individually charge my batteries outside of the device to check individual mAH capacities, so choosing multiple strings which are not paralleled together, just wired in series..
    Last edited by Laser57; 04-04-2022 at 07:59.
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  2. #2
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    I couldn't get the link to Joom to work, so I'm not exactly sure what you're looking for, but if you just want to group a bunch of 21700 batteries in a circle (more or less), why not just jam three individual holders together and wrap the whole mess in shrink-wrap? See this link: https://www.digikey.com/en/product-h...attery-holders This would make it easy to wire the cells together in whatever series/parallel arrangement you wanted.

    The link you posted to e-bikestuff showed an interlocking hexagonal battery holder that grips the end of the battery, but it was for an 18650 cell. I see that they do sell the same thing for the 21700 cell, however. So a pair of those for each cell would probably give you the most compact grouping, but you would still need to attach your wires to the battery ends, which could get messy. (Typically, I've seen that done with a spot-welder, but you could probably use a soldering iron so long as you were careful not to overheat the battery.) And I think you'd still want to wrap it all in shrink-wrap (or something) to keep everything together once you're done.

    Adam

  3. #3
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    Thanks for the suggestion, that would work and may be the solution I will be forced to use. I would prefer to find a battery holder which will allow me to insert them into it and remove them for individual charging and checking of individual mAH capacities over time but that isn't a deal breaker on the project. I am betting someone makes what I'm looking for, just haven't found them yet. If nothing else, I suppose I could hire someone to machine a 21700 cell holder pack for me which holds three sets of three cells in series, perhaps four sets. I am not in a hurry and the expense of a custom battery holder can be borne due to that. Anyone know of a good machine shop who can do that kind of work, perhaps has done so in the past for battery packs?

    Chris

    PS: I fixed the 21700 link, the joom link worked for me just now using my Qatar IP, but not when I used a state side VPN, it appears they won't allow access to that link unless in the country it was created in/for. I've attached a photo of a similar battery holder, below, but again for AA batteries where I want to use the 21700:

    Click image for larger version. 

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    Last edited by Laser57; 04-04-2022 at 08:20.
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  4. #4
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    Quote Originally Posted by Laser57 View Post
    Anyone know of a good machine shop who can do that kind of work, perhaps has done so in the past for battery packs?
    Hi Chris,

    Hmmm. A machine shop could certainly make the holder, but that is going to be expensive. I think this is a job that is better suited for a 3D printer.

    Do you know anyone who has a 3D printer? Worst case, there are a few people here on the forum that would probably be willing to do a custom run for you for very little cost. (Or you might want to buy a printer for yourself - these days they are under $300!) A simple filament printer is all you would need for this.

    I don't have one myself, but I've been thinking about getting one. There's just too many times where I've thought to myself, "Damn... If I had a 3D printer I could make this part myself in about an hour, rather than waiting 2 or 3 days for it to be delivered from some on-line shop."

    I took a quick look at ThingVerse (web archive of public domain 3D designs you can download for free) to see if anyone had uploaded any models of 21700 battery holders, and I found quite a few. In particular, I think this modular design, which clusters 3 batteries in a cylindrical arrangement and can be expanded vertically to get higher voltages, is more or less what you are looking for. You'd still need to figure out a solution for the connections on the ends, but it appears that the design is meant to use some sort of off-the-shelf spring-steel plate that slides into the notches on the ends.

    Out of curiosity, what are you planning to use the batteries for, and why do you want/need them to be in a cylindrical configuration? Because if the form factor isn't a big problem, you might want to consider using a Lithium-Polymer battery instead. Example: This 3S, 5000mah pack comes in a long, rectangular plastic shell and sells for $23. It has the same capacity as the 21700 batteries you were planning to use, and it's rated for 50C discharge, which is a crazy amount of current. Best thing is that it's fully encased, so you don't need a custom holder. You can still use the balance connector to monitor the voltage of individual cells, and if you have a balance charger, it will make sure each cell is charged to the same level. Just a thought...

    Adam

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