Module Step-by-Step Procedure

Important notes before getting started

Please refer to https://docs.google.com/spreadsheets/d/13xwf5e_5ykVG42IyagU8_QQN1EIVY4WaOXtT-j7fQOg/edit?usp=sharing to ensure you are using the correct hardware. Working on a module, please update the number of hardware components used in the inventory page of the sheet so we know what we are running low on.

 

Cells we’re using: LG 21700 M50

Procedure:

  1. Add heat set inserts to the appropriate locations

    1. Side note: M2.5 heat-set insert holes on the top module cover could be bigger to make melting them easier (not urgent)

  1. Bend sigma-clad tabs after fitting them to the top plate

    1. Place Sigmaclad between top plate and top cell holder into the appropriate location (should lock in place with the side protrusions)

    2. Attach the top plate, using the heat set inserts previously installed with M3 screws

    3. Bend the Sigmaclad terminals as close to the 3D-printed wall as possible. Should look like the photos below

  1. Remove the top plate and use MG Chemicals 8800 to attach Sigma Clad to the top cell plate (the Sigma clad should align flush with the top cell plate holders)

    1. Begin with measuring the materials in a 2-to-1 ratio of liquid A and B, respectively. Approximately, 2.5mL of A and 1.25 of B should be sufficient for this step. Solution A needs to be shaken before poured, it should look black like in the image.

    2. Use the heat gun to apply heat to both liquid A and B to rid any air bubbles

    3. Pour mixtures into the same container ensuring to scrape excess material from the side of the container to get as much as possible

    4. Use heat fun again to briefly flash heat (not too long as the mixture will set faster after cooling)

    5. Mix mixture for 2 minutes

    6. Wait until the material has reached a viscous state that is easier to work with (still liquid but congeals together better than the freshly mixed liquid)

    7. Gently place the mixture onto the top cell plate (preferably with a popsicle stick or something to apply)

    8. Press on the Sigma clad to their according sides of the module

    9. Use clamps to hold down Sigmaclad, placing popsicle sticks down across the material ensures more of the surface area of the Sigmaclad contacts the cell plate

    10. Leave for a minimum of 2 hours before moving, it takes 24 hrs to fully set

    11. Once finished setting, remove any extra material and wipe the sigma clad with rubbing alcohol to clean the surface

  2. Attach standoffs to the bottom cell holder

    1. Begin by using LOCTITE SF4769 on the interior of an aluminum standoff

    2. Place LOCTITE 262 on the appropriate screw for the stand-off (6-32 Thread Size, 1/2" Long Bolt, refer to Master BOM to find it)

    3. Screw together the connections using an allen key to make sure it is secured

  3. Solder voltage tap wires onto Sigmaclad tabs after setting is complete

    1. Cut 4 wires to ~1 ft in length

    2. strip one end of all 4 wires

    3. Coat the end of the stripped wire with solder

    4. Add flux to the Sigmaclad tabs and begin heat up the tab

    5. Melt a pool of solder of the tab

    6. solder the wire and Sigmaclad together, important to keep the solder clean and close to the surface so it fits through the top plate cover later on

    7. Heat shrink the connection with ~2 cm of heat shrink

  4. Feed nickel voltage taps through the bottom plate in the following configurations, paying close attention to the holes in which the wires go into

    1. Tape up the nickel strips so there is no contact with the cells and the strip

  5. Place cells in the correct placement

    1. Begin with filling the first parallel line with cells, positive side upwards. Positive ends of the terminal should be where the 3D protrusions (bumps) are on the 3D print

    2. Place tape on the top of cells

    3. Then place the 2nd pair of parallel cells, which should have the negative side up this time (it is a 8P4S, so rows of series cells)

    4. For the modules located in the center, place thermistor on the center of the cell using kapton tape, ensure it is secure.

    5. Push wires to side and continue placing cells in parallel groupings, continuously taping up the top of the cells

  6. Add top cell plate holder using the same bolt process in step 4, note how the cells are still covered with tape.

  7. Spot weld the connections

    1. Refer to the Spot Welding guide to use the Spot Welder

    2. Cover the Sigmaclad with electrical tape where they are bent upwards.

    3. First, spotweld the cells in parallel

      1. measure out the nickel strip needed by laying the nickel across the parallel direction and making indentations where the cell holes are located. This is not enough current to be dangerous but to be extra safe, there are electrical taped bolts that can be used, this also creates more accurate strips

      2. Spot weld the parallel connections until completed

    4. Continue to do so for the series connections, making sure to solder the voltage taps in the appropriate places (shown below for the bottom plate, for the top plate there is only the center area for the 2-wire voltage tap and its location is made clear from the indentations on the cell holders)

    5. For the sigma clad connections spot weld 2 connection points from the nickel to the sigmaclad

  8. Potting material in top cell plate following step 3 for the potting material

  9. Place the top cover on the top cell holder, using LOCTITE SF 424 on the M3 bolts. This should be done while the potting material is drying.

  10. Pour an adequate amount of potting material into the bottom cover plate, enough to fill the surface but not cause overflow.

    1. Align the module onto the bottom cover, making sure the male and female protrusions are aligned.

  11. Clamp all pieces together ensuring all gaps between the top and bottom plates are sealed and let cure for 24 hours.

  12. DONE!