I have been working on parameterizing the OpenSCAD file. I have it to where you can use it for:
1) any size cell (i.e. 18650, 21770, DDLLL)
2) change the wall thickness (battery separation)
3) change the number of facets (smoothness of the circular cutouts)
4) size of the bus notches
5) thickness of insulator
6) size of hole
7) depth of battery recess
I wanted to parametrize the rows and columns of cells however I hit several limitations in the OpenSCAD language. Thinking that there is 'strength in number' and that 3D printing is basically a repetitive 'one shot' process
(as opposed to something like injection molding) I started working on increasing the number cells in a cap. [strike]At 5Sx2P I exceeded the practical limit of OpenSCAD's rendering engine. Fortunately FreecCAD can load the program and is cable of rendering it.[/strike] I had hoped to expand the matrix up to 13Sx4P
(popular configuration for nominal 48 volt battery) [strike]but I am quickly coming to the conclusion that size project may require a professional level modeling program such as SolidWorks or BricsCAD.[/strike]
EDIT: Found my configuration problem with OpenSCAD
I am attaching the parameterised file for the 5x2 configuration for anyone that wishes to play with it.
REFINEMENTS:
Slightly larger battery cavity diameter: OpenSCAD use facets rather than real circular curves. In any case any program that generates and STL file is is going to use facets. The cells are not exactly 18.0000mm in diameter. In my experience they very from undersize to oversize and that does not include the insulating label attached around the cell. Thus I have increased the diameter by 0.25mm thinking that sanding the inside of the each battery cavity would be a royal pain in the most southern region.
Cell Separation: At first blush some would probably not thick an extra 1mm wall thickness would matter much. However for a 13S battery it will increase the length by one inch. I set the minimum wall thickness to 0.5mm which results in a airspace of 1mm between the cells.
Conductor (Buss) Notches: If the notches for the conductor could be made the same size then the individual modules could be rotated as need for optimum configurations. To illustrate this I have set the notches to 6mm widths.
Facets: For development work I have set the number of facets for the holes at 30. For producing a actual STL file for printing I would recommend using 60 or even 90 facets to produce and much smoother part. However I note that this resolution may be smaller than a particular 3D printer is capable of replicating --- something that needs to be verified. Increasing the number of Facets can greatly slow down the rendering engine but it is a one time job for the STL file.
Any of the previous items can be changed in the top of the parameterised SCAD program file.
Code:
// cell diameter, slightly oversize
// od = 18.25; // 18650 outside cell diameter
od = 21.25; // 21700 outside cell diameter
dp = 5.0; // depth of cell hole
id = 12.0; // Inside opening diameter
// This gives 1mm seperation (air) between the cells
wt = 0.5; // minimum wall thickness
// buss notch sizes
ww = 6.0; // wide bus width, full length
nw = 6.0; // narrow bus width, across rows
bh = 2.5; // bus height, thickness
ih = 0.5; // insulator height, thickness
// -------------------------------------------------------
af = od+(2*wt); // Across Flats of Hex
// facetts, controls how "circular" the hole is
// at least 60 recomended for production
// increasing this slows computer -- a bunch
//ff = 30; // for testing and development
ff = 60; // for production
//ff = 90; // not recommended
EDIT:
FYI this part is about $14 if done by Shapeways in white plastic
Maybe not the most economical but I wanted some kind of guess ...
https://www.shapeways.com/about
Questions:
Assuming that 5 long and 4 wide is the practical limit as this point, what are the optimum size modules under that (each one being a separate program file).
View attachment Hex Cell Caps - 5Sx2P.scad.zip
EDIT: I also now have the 13Sx4P design file (
aprox 10 x 2.9 inches)... if anyone wants/needs it then PM me.
I made some changes for cost reduction and now have the price down to: $33.50
(you would need two for a pack)
Code:
od = 18.00; // 18650 outside cell diameter
dp = 3.3; // depth of cell hole
id = 12.0; // Inside opening diameter
// This gives 1mm separation (air) between the cells
// *** *** may have to increase to 0.7 *** ***
wt = 0.5; // minimum wall thickness
// buss notch sizes
ww = 8.0; // wide bus width, full length
nw = 4.0; // narrow bus width, across rows
bh = 2.0; // bus height, thickness
ih = 0.7; // insulator height, thickness