Update! Building the battery pack
Turns out its quite hard to fit a 12S6P 21700 battery pack inside a Peli 1200 case, so this was more work than I expected. I was going to use standard hexagon 21700 cell holders, but it was impossible to fit the cells inside the case using this configuration, so I had to design and 3D print a custom cell holder.
The cell holder consists of two 3D printed end caps and is held together using hexagonal M4 stand-offs and M4 screws. The LLT Smart BMS is mounted to the side of the battery pack, and there is free space next to it for the for the output/charging wires and connectors. I’m quite pleased with how this turned out, all the cells are mechanically secured and don’t rely on the spot-welded nickel strip to hold them in place The 3D printed end caps are 10mm thick and 3D printed out of durable ASA plastic and the M4 metal standoffs have heat-shrink around them to insulate them in case of malfunction.
Before I began spot welding the cells together, I double checked that the cell holder assembly fitted into the Peli-case, it was very snug
First, I attached self-adhesive fish paper rings to all the positive cell terminals and measured the voltage of each cell, they were all 3.54V ±0.01V. I then proceeded to insert all the cells into the holder and bolted the cell holder assembly together using Loctite thread locker, and then spot-welded all the parallel groups.
The next step was to spot-weld all the series connections. At the positive and negative terminals at the end of the battery pack there are 10AWG cables soldered the entire length of the P group, unfortunately I forgot to take pictures of this process. I used 0.2mm nickel strip throughout this build.
All the nickel strip that is not located in a deep recess had its corners rounded, so doesn’t cut through anything and the BMS wires are soldered onto the balance wire tabs.
Finally, the top, bottom and sides of the battery pack were lined with fish paper and secured with fibreglass tape. The Smart BMS Bluetooth module is secured to the top of the battery, you can see it blue status light glowing through the tape.
I was planning on heat shrinking the entire pack but the charging and discharge cable positions kind of stopped me from doing this, and there isn’t enough room in the Peli case to have the wires easily protrude out of the end of the pack. So, I opted to heat-shrink the pack in two sections with a gap in between them where the cables come out. The pack output has an anti-spark XT90 connector and the charging is done via an XT60 connector.
Currently you must open the Peli ase to charge the battery, I might add an external charging port in the future, but not sure if it’s worth it.
I would like to say big thankyou to @Halbj613 for setting up the spot-welder lending group, that Flipsky spot-welder worked real good and borrowing instead of buying saved me a lot of cash