Bicycle light battery case

thingiverse

There are many affordable and extremely bright headlights available on the market, but most come with low-quality batteries. Meanwhile, high-quality 18650 Li-Ion cells are widely used and easily accessible, yet rarely found in end-user products as separate cells. Here's a battery case that allows for easy replacement of cells while on the go, providing energy for several nights at very low cost. It is highly recommended to use protected cells, which can be removed from the case and charged separately using a universal charger. I provide a package of 3D-printed parts (battery case, different case mounts) that can be assembled with additional parts (battery connectors, cable, plug). Along with 18650 cells, a charger, and a headlight, it forms a high-end MTB light bundle. The battery pack provides an output voltage of 6.4 to 8.4V and must be used with an appropriate headlight that works on this voltage. The case consists of three parts: the bottom and main part glued together, and the removable lid. First, cut the female end of the cable to ~300mm (or your preference) and thread it through the main part's hole pointing towards the bottom part. Solder each wire to the positive (truncated cone - red wire) and negative (spring – black wire) contacts respectively. Bend the connectors' connectors backwards so that the soldered connection can fit in the bottom part's slot. Remove 30mm of insulation from the cable, strip the last 10mm, and glue the battery connectors to the bottom part, ensuring they are centered. Glue the main and bottom parts together, making sure the cable is properly glued for stress relief. Use 2K epoxy resin. In the lid, short positive and negative connectors (series connection of cells) by soldering them together and gluing them to the lid. The connectors' seat may be tight; cutting their edges slightly can help if the "double-connector" doesn't fit. Glue an M4 screw into the knob and the M4 nut in the slot of the battery case. Parts to order: Cable: Female connector (5,5mm x 2,1mm DC jack, watertight and lock-in plug) + min. 300mm of 20 AWG cable http://kaidomain.com/S024776-5_5mm-x-2_1mm-Male-to-Female-20AWG-Extension-Cable-100cm-Length Connectors: 18650 cell connectors with 16x16,5mm base and rounded edges (see picture, as “18650 connector” everywhere on eBay/aliexpress) Screw: M4 hex screw (min. 26mm) and M4 hex nut Velcro strap: 20mm width and ~200mm length for fixation on the mount. Drone battery straps work well: https://www.banggood.com/5PCS-Banggood-Battery-Tie-Down-Strap-for-RC-Multirotor-p-1067255.html?cur_warehouse=CN Parts to complete the bundle: Protected 18650 cells: I use Panasonic NCR 18650B Protected 3400mAh (Green) cells (protected from short circuiting, overcharge, and undercharge). A very good overview can be found here: https://lygte-info.dk/review/batteries2012/Common18650comparator.php and https://lygte-info.dk/info/batteryIndex.html. The case is designed so that even the very long protected cells (up to 70.5mm) fit inside. Charger: A good overview is given here: https://lygte-info.dk/info/indexBatteriesAndChargers%20UK.html. I use the LiitoKala Engineer Lii-500. Mounts: I provide three mounts for flat surfaces/tubes, for positioning parallel to a tube with some space (i.e. half below the stem clamp on a handlebar) and for positioning at 90° angle to a tube. All mounts are fixed to the frame with two cable ties and the battery can be fixed on the mount with a non-elastic Velcro strap (mount and velcro stay fixed, battery easily changeable). All parts should be printed in ABS. The case needs to be printed with 100% infill, the mounts can be printed at 50%, but some solid outer layers are recommended. The production procedure is quite laborious. Especially the dovetails between main and bottom part of case often need to be cleaned. Besides that, it is challenging to assure a proper gluing that guarantees a decent fit of connectors and batteries. Any remark/suggestion for improvement is welcome.