Battery Pack Assembly

The goal of this project is to create a battery pack from purchased power cells. Is important to understand how cells can be connected to increase energy output and how battery performance can be evaluated from internal loadings. Applications of this can extend to several products such as R/C vehicles, Phone Chargers, etc.

*SAFETY NOTE: Some sparks may occur when using spot welder, assemble this package away from flammable objects*

1. 2x 3300mAh 18650 lithium ion battery cells
2. 1x 2S battery management system (BMS) board
3. 1x male/female XT-30 battery connector pair
4. 4x pure nickel battery tab (.15mm thick, 8mm wide)
5. 2x 14 gauge battery lead wire
6. One piece large shrink tube (to wrap battery pack)
7. Spot Welder

Using a spot welder, attach one nickel tab to B+, one to B-, and one to BM

1. Orient power cells so that when batteries are in vertical position, one cell has negative end (Cathode) up and one has positive (Anode) end facing up.
2. Using spot welder, attach B+ tab on BMS to the Anode, B- to Cathode, and BM to both Anode and Cathode of reverse ends of power cells (May need to add an additional nickel tab to be able to make the connection in series)
3. To activate BMS, it may be needed to short the terminals

1. Place shrink wrap around pack and carefully apply heat until wrapping is secure
2. Attach battery to charger with desired connector. Ensure charger settings match the amount of cells in series as well as rated voltages/Amps.

1. After battery is charged, it is needed to check the internal resistance of the pack. To do this, first, using a multimeter, measure the open circuit voltage between the positive and negative terminals of the battery output (record this value). Next, apply a 5 ohm resistor and measure/record voltage. Finally replace the 5ohm resistor with a 25ohm resistor and measure/record again.
2. Using the values measured above, follow the calculations taken in the above image to solve for internal resistance of the pack.

1. Attach battery pack to a BD-250 battery discharger
2. Using the BD-250 Software, set battery type to Lithium Ion, 2 Cell, Desired final charge state, and discharge current to a value less than the battery is rated for (Can choose any value below this, but heating will increase if too much current is drawn)
3. Click start on battery analysis software and wait until final state is reached.
4. The images above are examples of what the discharge performance will look like. (NOTE: all batteries will vary in performance due to workmanship in the construction of the cells.) Power and performance over time will be visible from the provided information.