DIY variable voltage 18650 holder- Mtbr.com
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  1. #1
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    Idea! DIY variable voltage 18650 holder

    First off, not to knock TurboFerret and what he has evolved into a nice product, but in the spirit of DYI and being on the cheap, here's what I did.

    My goal was to create a cheap holder for 18650 cells in serial that I could use in the camel back for various emitter count helmet lights. I'm satisfied with using 14.4v packs in water bottles for the bar lights, so for this project waterproofing was not high on the list of priorities.

    What I ended up with is a holder that will fit anywhere between 1 and 5 (or more) 18650 cells in serial, and all in for less than $15.

    I know many have played with PVC and various pipe and tubing, and I started down the same path by taking a protected Trustfire cell to Lowes and test fitting in every type of round pipe I could find. It turns out that these cells, at least the Trustfire and Ultrafire, fit perfectly snug in a 3/4" schedule 80 sprinkler riser, so I bought a few different length risers and some caps.



    For contacts, I used a $1.50 C cell holder, just cut out the plastic and springs and bent them as needed, soldered the wire, then potted them in a PVC cap with 5 minute epoxy, again nothing new here.



    and the donor C cell holder.....



    So to play with the riser lengths, I ripped a 12" riser down the center and started cutting to size making sure to load the springs correctly. I also found that rare earth magnets helped to "find" and hold the contact between the battery and springs.



    And at this point I realized that with some variable length in the wire, I could have a single set of caps/contact points that would be flexible enough to accommodate a range of voltage using a variety of cell count, and ended up with this.....



    holding a single cell....



    holding two cells...



    I've already verified that the coil wire will safely stretch long enough to hold 5 cells, the only added cost being the dollar or two for the needed schedule 80 pipe. An added benefit is that the coil tension keeps a nice pressure on the end caps, although they fit tightly enough on their own to keep from slipping.

    From here, I want to find a more robust cable strain relief on the connector side. The 20g teflon wire is bedded in epoxy so it's tight there, but I see how the coil could put some excess pull on that wire. For now the o-ring is assisting and seems to be sufficient, so maybe I'll just notch the PVC and glue that in place.

    And I just had another thought, since all 3/4" PVC is a common 1.05" OD, but different schedules and classes offer varying ID's, maybe this same endcap set could be used for other batteries as well; like using class 200 pipe (thin walls) with size C cells........

  2. #2
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    Me likey . I did something similar with C or D cell ni-cads in a 15 inch sprinkler body (I forget which - this was about 10 years ago for my MR-11 halogen DYI project).

    While not as pack friendly as a four cell 'flat pack' or 2x2 'cube' - there is an advantage to making a baton-like battery pack... gives you something to wack the occasional mountain lion or coyote over the head with!

  3. #3
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    A similar try on my part was not successful. When I stacked 5 batteries inline the weight of them would compress the spring when hitting a big bump, breaking the circuit. Heavier spring maybe? I just changed the design to this.

    http://forums.mtbr.com/showthread.php?t=501179


    Not as simple but totally reliable so far.

  4. #4
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    Quote Originally Posted by Vancbiker
    A similar try on my part was not successful. When I stacked 5 batteries inline the weight of them would compress the spring when hitting a big bump, breaking the circuit. Heavier spring maybe? I just changed the design to this.

    http://forums.mtbr.com/showthread.php?t=501179


    Not as simple but totally reliable so far.
    I did see your design, very nice, it looks factory made.

    I admit I haven't put any hard riding on the pack yet, and I may need to tune the length of the pipe and/or springs if I experience the same disconnects when pounding the rough terrain. The C holder springs are pretty stiff, and theres always D holders which are even more stout. I'll get a good ride in this week with some steep drops and jumps and see how it does.

  5. #5
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    Quote Originally Posted by dsjc
    ....My goal was to create a cheap holder for 18650 cells in serial that I could use in the camel back for various emitter count helmet lights. I'm satisfied with using 14.4v packs in water bottles for the bar lights, so for this project waterproofing was not high on the list of priorities...What I ended up with is a holder that will fit anywhere between 1 and 5 (or more) 18650 cells in serial, and all in for less than $15....

    .....From here, I want to find a more robust cable strain relief on the connector side. The 20g teflon wire is bedded in epoxy so it's tight there, but I see how the coil could put some excess pull on that wire. For now the o-ring is assisting and seems to be sufficient, so maybe I'll just notch the PVC and glue that in place...
    Bravo!! ( *Clap-clap* ) Nice work! I just wish there was some way on the forum that you could save a thread without having to look it up when you need it.

    To help keep the end caps together maybe you could cut a length of old inner tube, glue a couple pieces of Velcro to each end ( or just glue the ends of the inner tube together ) and then stretch it around the whole tube...just a thought.

  6. #6
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    That's a pretty good idea and I think I'll borrow it for my helmet lights.

    Quote Originally Posted by Cat-man-do
    Bravo!! ( *Clap-clap* ) Nice work! I just wish there was some way on the forum that you could save a thread without having to look it up when you need it.
    Go to the "Forum Jump" drop-down at the top of the page, select "Subscriptions." The threads that you've posted in are displayed there.
    Slow-core. -.. .-. .. -. -.- .... --- -- . -... .-. . .--

  7. #7
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    Quote Originally Posted by Cat-man-do
    Bravo!! ( *Clap-clap* ) To help keep the end caps together maybe you could cut a length of old inner tube, glue a couple pieces of Velcro to each end ( or just glue the ends of the inner tube together ) and then stretch it around the whole tube...just a thought.
    There are, of course, threaded risers and end caps that should keep everything together... don't have any lying around my office at worky - but when I get home I'm gonna check it out.

  8. #8
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    Quote Originally Posted by dsjc
    I did see your design, very nice, it looks factory made.

    I admit I haven't put any hard riding on the pack yet, and I may need to tune the length of the pipe and/or springs if I experience the same disconnects when pounding the rough terrain. The C holder springs are pretty stiff, and theres always D holders which are even more stout. I'll get a good ride in this week with some steep drops and jumps and see how it does.

    I am sure you can get this to work. I used a spring salvaged out of a cheapo 2 C cell flashlight when I tried the pipe design. There is no reason that the spring needs to be from a battery holder or flashlight. Go to a good hardware store if you need a stronger spring.

    .

  9. #9
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    Quote Originally Posted by abacojeff
    There are, of course, threaded risers and end caps that should keep everything together... don't have any lying around my office at worky - but when I get home I'm gonna check it out.
    My original intent was to use threaded caps, and I brought home a handfull of threaded and slip. Once I got working with it, I decided against the threaded since I didn't want to be twisting the contact springs against the batteries inside without seeing or "feeling" what was going on, and it seemed the wiring would be all twisted after threading the cap(s) in place.

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