Project 1 Mechanical design of battery pack

Mechanical design of battery pack capacity 18kWh

for the Design of the battery pack used the following cell (Datasheet)

Desing Assumptions are as follow:

1) Battery energy = 18 kwh

2) Voltage (to run the vehicle) = 400V

Stage 1st: battery pack configuration

To calculate the number of cells required for the battery pack

Number of cells (N) = energy / (nominal voltage*capacity)

N = 18000 / (3.3*2.5)

N = 2182

We need a minimum of 2182 cells to get 18 kWh energy, now based on that, we need to decide on configuration – series and parallel.

And we assumed 400 Volts are needed to run the vehicle.

The nominal voltage of one cell is 3.3 V

Number of series cells required to produce 400 V (Ns) = voltage required / nominal voltage of one cell

Ns = 400 / 3.3

Ns = 121.21 = 122

122 cells are connected in series will generate 400 voltage and the capacity of the whole module will be 2.5 Ah

Now we need to find the number of cells which will be connected in a parallel configuration

Np (cell in parallel) = total cell / Ns

Np = 2182 / 122

Np = 17.8 = 18

Hence we take 18 cells for each parallel row, and although it is exceeding the required capacity, that is negligible.

Cell architecture = 122 Series and 18 Parallel = 122S18P

The capacity of battery pack is,

Capacity = parallel cell row*individual cell capacity

Capacity = 18 * 2.5

Capacity = 45 Ah.......... mean that battery supplied 45 amp current per hrs (C- rate)

Range :

Let’s powertrain energy consumption = 100 Wh/km at 70% powertrain efficiency

Range = Capacity/energy consumed per kilometer

Range = 18000 / 100

Range = 180 km

Stage 2nd: battery pack dimensions and weight

battery pack dimensions:

Length of casing (L) = number of cells at series*(cell diameter (26) + margin at both side of cell (4)) + clearance at side (diameter of edged cell + margin)

L = 122*30 + 60

L = 3720 mm

Breadth of casing (B) = number of cells at parallel*(cell diameter (26) + margin at both side of cell (4) + clearance at side (diameter of edged cell + margin)

B = 18*30 + 60

B = 600 mm

Height of casing (H) = 65+35 (Height of cell + margin for wiring ,Cell holders and metal strips)

H = 100 mm

Weight of battery pack

Cell weight = 76g

Number of the cells = 2182

Battery pack weight (W) = cell weight*number of cells + weight of accessories

W = 76*2182 + 4.5 = 165.8 + 4.5 = 170.3 kg

W=171 kg

Stage 3rd: battery assembly

The cells are gone through the following process:

battery pack ready to use of 18 kwh