Project 1 Mechanical design of battery pack
Aim :
To prepare a detailed battery pack drawing along with its enclosure and state assumptions
In this Project, we'll figure out all the numbers needed to construct an EV battery pack. For our battery pack, we're going to use Cell: ANR26650M1-B. All electrical factors, including temperature, Depth of Discharge, Operation Current, Energy Density, Work Cycles, Battery Capacity, State of Charge (SOC), State of Health (SOH), and Ampere-Hour (Ah) Capacity, will be taken into account when determining parameters. Additionally, we compute every geometrical factor, including size, weight, volume, area, etc. Finally, we take into consideration a few different battery pack container models.
Battery pack architecture :
Battery cells are organised in strings and modules to form the basis of all high voltage battery packs. A battery cell can be thought of as the voltage's smallest division. Modules made up of individual battery cells can be arranged in parallel or series. Additionally, battery modules can be linked in series or parallel to form a battery pack. There may be different levels of flexibility depending on the battery's specifications. The quantity of series-connected cells determines the voltage of the entire battery pack. For instance, the sum of the individual voltages of six cells connected in series will equal the total (string) voltage of those cells.
Battery pack production line :
In order to build a battery pack, we must first determine the voltage needed to support the vehicle's whole weight. As noted earlier, we had assumed a 400V system. The battery modules should then be designed so that the overall voltage matches the voltage needed to power the load. Individual cells can be connected in series or parallel to build the modules. The final battery pack should then be constructed by connecting all modules in series and parallel. Voltage is added via a series connection while the current stays constant. Current is added while the voltage is kept constant in a parallel connection. In this instance, the voltage of a single cell is 3.3V, and its capacity is 2.56Ah. 8.25Wh of energy are provided by a single cell. Therefore, we require around (18000/8.25=2162) cells for an 18KWh battery pack. In order to meet our load demand, we must design a single module that can provide 400V. Therefore, cells are connected in series so that voltage is added while current is kept constant to provide an output of 400 V. The approximate number of cells needed to produce 400V is (400/3.3=122 cells). As a result, a single module produces 400V from 122 cells, but the energy it produces is insufficient to power the car because the motor has a greater power rating. A single module produces (122*8.25Wh=1006.5Wh) of energy. In order to link the modules in parallel and build a battery pack of 18KWh while keeping the voltage under 400V, The voltage in these parallel connections stays at 400V as the currents are applied. As current rises, the battery pack's power rises to support the high power rating motor load. To get an 18KWh battery pack, we must now determine how many comparable modules should be connected in parallel. Calculating (18KWh/1006.5Wh =17.88) reveals that nearly 18 similar modules need to be connected in parallel to produce an 18KWh battery pack. As a result, the battery model is described as having 122 series and 18 parallel connections, giving us (122*18 = 2196 cells). From this, we calculated the battery pack's overall capacity, which is just over 18 KWh (2196*8.25Wh=18117Wh). The battery pack's total capacity is given as (2.5Ah * 18 = 45Ah). This indicates that it continuously supplied 45 A of current for one hour till complete discharge. In order to accommodate 18 modules into an EV chassis, they must be placed similarly to a battery pack.
Procedure :
1) The cell computation must come first.
2) After that, battery pack assumptions will be made.
3) After making assumptions, we must calculate the battery pack.
4) Using Cell Dimensions, we determine how much surface area a battery pack needs.
5) Based on the aforementioned calculations, we construct the battery pack.
The battery pack's complete cell (Cell: ANR26650M1-B) specifications are listed below :
We will calculate additional parameters from the ones mentioned above that are used in the construction of battery packs.
100% DOD, various cell discharge rates, and cycle life performance -
Characteristics of Constant Power Discharge at Cell 23 °C -
Temperatures for 2.5C Constant Current Discharge -
High-performance LiFePO4 (nanophosphate lithium iron phosphate) battery technology from A123 provides high power and energy density along with excellent safety performance and extensive life cycling in a lighter weight, more compact package. Our cells' low capacity loss and impedance growth over time, combined with their high usable energy over a broad state of charge (SOC) range, enable our systems to satisfy end-of-life power and energy demands with a minimum amount of pack oversizing.
Dimensions :
Cell calculation :
Volume of the cell: The formula for the volume of a cylinder is used to calculate the volume of the cell.
hence, the equation is πr^2h
We have the values for "r" and "h" from the Datasheet of Cell.
r=0.013m and h=0.065m = Volume of the cell: πr^2h
: 3.14 * 0.0132 * 0.065
: 0.0000344929 m^3
In essence, the volume of the cell value is utilised to calculate the battery pack's overall volume.
Cell Energy= Cell Capacity (Ah) × Cell Voltage (V)
= 2.5 × 3.3
= 8.25 Wh
The total energy of the battery pack is calculated using the value of a single cell.
Single Cell Energy Density
Volumetric energy (Wh/m3) = Single Cell Energy / Volume of each cell
= 8.25 Wh / 0.0000344929m^3
=2,39,179.6572 Wh/m^3
Battery pack assemptions :
44 cells are in parallel with 50 cells in series, and as previously said, we'll be using ANR26650M1-B cells.
Battery pack calculation :
Now that we have calculated parallel and series combinations, we can determine the overall number of cells needed.
Total no of cells: Series cells * parallel cells
:50*44
:2200
We can therefore compute the battery pack's voltage and current using a series and parallel combination.
Voltage= no of cell in series* nominal voltage.
= 50*3.3
= 165V
Current=No of parallel cells * cell capacity
= 44*2.5
=110Ah
Now that we know how much energy this combination has based on the product of its voltage and current, we can determine whether it will satisfy our requirements or not.
Energy= Voltage * Current
= 165 * 110
= 18150WAh
Therefore, our calculations meet the criteria that we set. Now that we know the total number of cells and the volume of each cell, we can determine the total volume needed for the battery pack.
Total volume = no of cells * Volume of single cell
= 2200 * 0.0000344929
=0.07588438 m^3
Additionally, we have the weight of a single cell, from which we can determine the overall weight of a battery pack devoid of other mechanical and electrical connections.
Weight = No of cells * weight of single cell.
= 2200 * 0.076
= 167.2kg
Energy dencity= volume * battery pack energy
= 0.07588438 * 18150
= 1,377.301497kWh/m^3
We currently have all the necessary parameters to physically create the battery pack.
| NO | Calculated Parameters | Result |
| 1 |
Cell Volume |
0.0000344929m^2 |
| 2 | Cell Energy | 8.25Wh |
| 3 | Cell Density | 239179.6572kWh/m^2 |
| 4 | Pack assumptions | 50s 44p |
| 5 | Total no of cells | 2200 |
| 6 | Voltage | 165V |
| 7 | Capacity | 110Ah |
| 8 | Energy | 18150WAh |
| 9 | Total volume | 0.07588m^2 |
| 10 | Total Density | 1377.30kWh/m^2 |
| 11 | Weight | 167.2kg |
Joining technologies of cells :
Various welding techniques are used to practise the linkages between cells and modules. Among them are,
Ultrasonic metal welding, Resistance welding, Laser beam welding, Wire bonding, Mechanical Jooining
Although cylindrical cells have low packaging efficiency due to their round cross-section, they have improved thermal management efficiency due to their compact shape. Here, I connect multiple cells using a positive and negative tab. Following is an illustration of how joining techniques can be used to construct battery packs using cylindrical cells:
