18650 Battery Frame

thingiverse

I tried printing modules on my 3D printer that could be assembled together to form a battery frame for an 18650 battery pack, starting with a small hex unit for a single cell with dovetails and coming to the conclusion that it was more trouble than it was worth. I decided to try larger modules instead. Most e-bike batteries are in the range of 36 to 60 volts, which is 10 to 15 cells in series, and they're also commonly 4 or 5 cells in parallel. The largest section size that I can print on my Creality Ender-2 is 5 by 5, so I decided to create the modules in both four and five parallel sections. A 36-volt battery only requires two FourByFive or FiveByFive sections to assemble a frame for each side of the battery pack. For more cells in series, a center section is needed. Those with larger printbeds can join the sections in their slicer program to produce the frame as a single print. The parameters I used for the design were: Height = 8.0 mm, Cell Hole Diameter = 18.60 mm, Cell Center to Center Distance = 20.00 mm, Mounting Hole Diameter = 3.0 mm, Mounting Hole Edge to Center Distance = 3.5 mm, Mounting Hole Center to Center Distance = 20, 40 or 60 mm, and Chamfer Distance = 0.80 mm. To determine the optimum cell hole diameter, I designed and printed a gauge in ABS and test-fit several cells into it to find the best fit. The size I chose was for a Samsung INR18650-25R that measures 18.30mm in diameter. There is some variance between the design size hole and the finished print. I had problems with bed adhesion and warping when printing these in ABS, so I used a large brim and a generous amount of hair spray to aid in cleanly removing the brim. To help with this, I incorporated 0.80 mm chamfers along the lower edges of the sections. The Tabs and Sockets used to join the sections together are intended for solvent adhesive bonding of the sections. I do not believe they provide adequate strength for an assembled battery pack on their own. I also encourage allowing sufficient time for the curing process. For bonding, I recommend one of the following: SCIGRIP #16 Acrylic Cement, IPS Weld-On #4 Acrylic Adhesive, IPS Weld-On #3 Acrylic Adhesive, Testors Model Comment #3509C, Methylene Chloride (99% pure), or Acetone (99% pure). I used SCIGRIP for testing because it was what I happened to have on hand. I suspect that IPS Weld-On #3 would produce the best bond. I find that XXXByOne sections are a bit flimsy, however they may be adequate in an assembled frame. The 3mm holes along the sides were the last feature that I added after discovering that one could acquire M3 Hex Socket head screws in 75 and 90 mm lengths. I need to ream the small holes with a suitable twist drill bit depending on if they are to be used as a clear through hole or threaded. All test prints were made using Paramount 3D ABS (PANTONE Battleship Gray 431C) 1.75mm Filament at an extrusion temperature of 225 degrees and a bed temperature of 100 degrees in 0.20mm layers, with zero fill and 8 to 10 walls to produce a solid print. Note that the left and right sides are opposite hand but the center sections (i.e. XXX-L-H and XXX-R-H) are interchangeable. For those with CAD systems capable of loading 3D DWG/DXF files with AICS solids, I have also included the original CAD DXF files. All design work was done with BrisCAD 18.x running on a Linux Mint 18.3 operating system. All referenced files are the exclusive work product of the author and placed into the Public Domain by the author 10 March 2018 without any warranty expressed or implied.