Project 1 Mechanical design of battery pack

Project 1:

• Battery pack capacity: 18 kWh
• Cell: ANR26650M1-B
• Prepare a detailed battery pack drawing along with its enclosure. State your assumptions.

Answer:

The specification of the battery is downloaded from online reference (Ref.: https://www.batteryspace.com/prod-specs/6610.pdf )

Based on the specification sheet and online data, compiled the below table for individual cell.

Manufacturer	A123-Systems
Type	Cylindrical
Model	ANR26650m1-B
Length [m]	0.065
Diameter [m]	0.026
Mass [kg]	0.076
Capacity [Ah]	2.5
Voltage [V]	3.3
C-rate (cont.)	10
C-rate (peak)	24
Energy [Wh]	8.25
Volume [l]	0.03452429
Energy density gravimetric [Wh/kg]	108.55
Energy density volumetric [Wh/l]	238.96
Required Energy requirement	18 kWh
Estimated wt. of Battery Pack	165.82 kg
Estimated no. of Cells	2182 Cells

Steps in the calculation of estimated no. of cells:

1. Based on battery dimensions, the cell volume is calculated in litres (L)
2. Mass of the individual cell is taken from spec sheet which is 76gms or 0.076kg

• The nominal cell capacity is 2.5Ah

2. Watt-hour (Wh) = Ah * cell volt (V) = 2.5 x 3.3 = 8.25 Wh
3. Energy density (Wh/kg) = 8.25/0.076 = 108.55 Wh/Kg
4. For the given scenario, the required energy requirement is 18kWh. The weight of the battery pack is estimated at 18000/108.55 = 165.82Kg

• Finally, the no. of cells needed for the battery pack is estimated as 165.82/0.076 = 2182 Cells.

Once we have a rough estimate of the number of cells needed, next step is to understand the number of cells to be connected in series and Parallel to form the battery pack. Based on the energy requirement, below the battery cell configuration proposed:

Planned O/P voltage	316 V
No. of cells in series	96
No. of Parallel cells	23
Actual no. of cells	2208

Steps in the optimizing the Cell configuration and calculating the actual no. of cells in this battery pack:

1. Output voltage is planned to be 316 V (assumption)
2. To achieve this voltage level, no. of cells that needs to be connected in series will be 316/3.3 = 96 cells.

• The remaining cells needs to be connected in parallel sets to get the requited energy requirement of 18kWh
  1. 2182 cells / 96 = 23 parallel sets
  2. Once the cell configuration is known, the actual figures are calculated as per below

1. The total no. of cells needed for the pack is 2208 cells (actual)
2. Hence the cell configuration of the battery pack proposed is 96S 23P.
3. The total energy capacity of the battery pack will be 2208cells x 8.25 = 18216 Wh or 18.22 kWh.

• Total weight of the battery pack would be: 2208 x 0.076 (kg/cell) = 81 kg.

Estimating the Surface area & volumetric energy density of the battery pack:

Below picture is only for symbolic representation (ref: https://voltaplex.com/7s12p-25.2v-42ah-li-ion-18650-battery-pack-lg-mj1-cuboid )

1. Length of the battery pack:
   1. Diameter of each cell x no. of cells in series = 96 x 0.026 = 2.496m (L)
2. Breadth of the battery pack:
   1. Diameter of each cell x no. of parallel sets = 23 x 0.026 = 0.598m (B)

• Height of the battery pack:
  1. This will be the length of each cell (if all cells are staked in single layer) = 0.065m (H)

1. Total surface area of the pack
   3. Surface area of a cuboid: 2*(LxB) + 2*(LxH) + 2*(BxH) = 3874 m²
2. Total volume of the battery pack: L*B*H = 0.09702 m³ or 97.02 L
3. Volumetric energy density of the battery pack is: 18216/97.02 = 187.756 Wh/L