18650 Battery Frame by lewtwo

Last crawled date: 3 years, 1 month ago

All this started out as a question that was posted on the EndlessSphere E-Bike forum regarding the practicality of printing modules on on a 3D printer that could be assembled together to form a battery frame for an 18650 battery pack. I tried a small hex unit for a single 18650 cell with dovetails and came to the conclusion that it was more trouble than it was worth. Thus I decided to try larger modules.
Most e-bike batteries are in the range of 36 to 60 volts which is 10 to 15 cells in series. They are 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 and I have to lie to Cura a bit to accomplish that. The Ender-2 has a bit larger print bed than some other 3D printers in the same price and size range. Thus 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 of you that have the luxury of larger printbeds can join the sections in your 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
Chamfer Distance = 0.80 mm
In order to determine the optimum cell hole diameter I designed and printed a gauge in ABS. I then test fit several cells into the gauge to determine the best fit. The size I chose was for a Samsung INR18650-25R that actually measures 18.30mm in diameter. There is some variance between the design size hole and the finished print. Some other cells such as UltraFire will be a bit sloppy.
As I chose to print these in ABS I had some problems with bed adhesion and warping. Thus I used a large brim and a generous amount of hair spray. To aid in cleanly removing the brim 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 to be used during the process of solvent adhesive bonding of the sections. I do not believe that 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)
Acetone (99% pure) … nail polish remover
I used SCIGRIP for testing because it is 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 I discovered that one could acquire M3 Hex Socket head screws in 75 and 90 mm lengths. I find that I need to ream the small holes with a appropriate twist drill bit depending on if they are to be used as a clear through hole or threaded. There are other methods that can be used to secure the two sides but this alternative is provided because it was convenient to do so.
All the test prints were made using “Paramount 3D ABS (PANTONE Battleship Gray 431C) 1.75mm Filament” with a extrusion temperature of 225 degrees and a bed temperature of 100 degrees in 0.20mm layers. I also had the extrusion factor down to 0.95 to maintain detail for for the tabs and sockets. There was zero fill with 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 that have a CAD system capable correct loading a 3D DWG/DXF file 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 of the 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. --- Enjoy ---