Build Instructions

Collapse

• 1

  NICKEL STRIP ASSEMBLY

  For connecting the cells in parallel, the best method is to use a spot welder with nickel strips.

  Directly soldering wires or strips to the terminals of lithium cells is generally considered bad practice, as the excessive heat generated during soldering can damage the cells, reduce their capacity, or, in extreme cases, create a serious safety hazard. This is why spot welding is commonly used for assembling lithium battery packs.

  One challenge I faced was that, because of the unusual cell arrangement used in this project, standard nickel strips would not work well. Therefore, I had to design a custom hexagonal nickel strip setup.

  For the spot-welding process, I got myself a portable spot welder.

  • The process begins by cutting the nickel strips into two different sizes, as mentioned in the Strip Size PDF. The longer 39mm strips are used to create the hexagonal shape for connecting the cells, while the smaller 10mm strips are used to create the L-shaped section that will allow us to mount the PCB above the nickel strip.
  • Using a custom 3D-printed jig, we first place the 39mm nickel strips into their designated slots to form a hexagonal shape. The second half of the jig is then placed on top to hold all the strips securely in position.
  • Next, using the portable spot welder, we spot-weld all the individual strips together, resulting in a single hexagonal nickel strip.
  • We then place the L-shaped section in its designated position on top of the hexagonal nickel strip.
  • The second half of the jig is placed over the entire setup to hold everything securely in position, and the L-shaped section is spot-welded to the hexagonal nickel strip.

  The result of this process is a custom hexagonal nickel strip that will be used to create the parallel connections in our battery pack.

  For this project, we need a total of eight custom hexagonal nickel strips.

• 2

  PARALLEL PACK ASSEMBLY

  • We begin the assembly process by first installing the four mid-support pieces onto the bottom cell holder and securing them in place using M2 screws.
  • Next, the LiFePO4 cells are inserted into the bottom holder with the negative terminals facing downward and the positive terminals facing upward.
  • The top cell holder is then placed over the cells and secured to the mid-support pieces using M2 screws. This firmly locks all six cells in place, completing the mechanical assembly of one parallel cell holder.
  • The electrical connections are made next. We begin by placing the custom hexagonal nickel strip on the positive side of the cell holder. Using a spot welder, the nickel strip is welded to the terminals of all six cells, electrically connecting them in parallel.
  • The same process is then repeated on the negative side of the battery pack using another hexagonal nickel strip.
  • Once both nickel strips are spot-welded, the connection PCBs are placed over the nickel strips and secured using M2 screws. Finally, the nickel strips are soldered to the PCBs, creating a solid electrical connection between the cells and the connection boards.
  • The same process is done on both the positive and negative sides of the cell holder, completing one fully assembled parallel battery module.
• 3

  TEST

  To verify that everything was assembled correctly, I measured the output voltage of the completed parallel cell holder using a multimeter. The measured voltage was approximately 3.27V, confirming that all six cells were properly connected in parallel and the assembly was functioning as expected.

  Since the final battery pack requires four identical parallel cell holders, I repeated the entire assembly process three more times until all four modules were complete and ready to be connected in series.

View all 11 instructions