Stackable, snapable 18650 battery case. Super easy DIY variable-voltage 18650 battery packs without pesky cell soldering, and allowing for simple cell replacement. (useful if using reclaimed 18650 cells from...say...laptop battery packs)
Disclaimer: 18650 cells can dump their power FAST. And this allows creation of *high voltage* packs. Which can burn, blow up, melt, and potentially kill you. These things can be *dangerous*. Be careful. Nuff said.
If you're the jump-to-the-chase type, here are the thingiverse and tinkercad links:
Thingieverse project now includes stl files for x5 and x6 cell versions
Step 1: The Problem
I wanted to build a high-voltage battery pack from laptop-reclaimed 18650 cells. (for an e-bike) DIY solutions either required soldering to the cells (heat bad for the cells, no good way to swap out bad cells), spot welding (spot welders for this application are $$, also no way to swap out cells that go bad), or building (somewhat) elaborate enclosures that allowed for battery replacement.
All these solutions also required sanding/grinding off all the nasty little bits of nickel strip that remained after separating the batteries from their laptop bodies.
Step 2: Solution
Inspired by and building on the 18650 battery case with integrated spring (here:http://www.thingiverse.com/thing:456900). I did some tweaking and came up with a solution that allowed for reasonably easy individual cell replacement while avoiding both heating the cell and the need to grind off the little residual bumpies. As a bonus, it’s extendable (adding/reducing voltage is trivial) and reasonably cheap. (assuming you can source a 3d printer)
Given the number of hours I spent printing and revising, I wouldn’t say I succeeded in creating a non-elaborate solution. For *you* however ... with some 12ga stranded wire, 8mm m3 grub screws and (optionally) 10mm pan head m3 screws and you too can have a tower of power.
Step 3: Details
The interconnect wire is 12ga stranded. It’s insulation is sliced (carefully) to expose 1/2 of the wire, for the length of the battery case. (see picture in previous step) Battery modules have holes @ each end for the 12ga wire. Stranded gives the best connection if you’re lazy as I am and don’t bother to smooth the battery ends.
m3 grub screws hold the batteries tight and squish the wire against the battery terminals. The holes aren't threaded, but are sized that the m3 easily cuts it's own threads.
The current model’s wire holes may be too small for 12ga wire. I drilled them out to fit.
Battery modules stack front-to-back to allow wire to loop from the + end of one set to the - of another. If they don’t snap together firmly enough for you, there are aligned holes for m3 pan-head screws to snug things together. This isn’t the optimum power-to-volume ratio, but it’ll work well enough for me to have the stack secreted away in paniers or in a bag mounted to a rear rack.
I haven’t actually used them in their intended application, as I realized that: I wanted 10ah minimum of range My recycled laptop cells averaged around 2000mah My recycled laptop cells generally aren’t rated for the load an ebike will put on them. I was out of season to ride the ebike, as fall had set in and I was driving kiddos to school every morning.
As a solution I’m thinking to build another stack to attach in parallel to the first. This should both double my range, and halve the amp draw on each set.