Challenge

Project 1 Mechanical design of battery pack

GGaurav Hole14 Mar 2022

1. Aim: -

To make Mechanical design of battery pack

2. Objective: -

Using the following information makes the mechanical design of the battery pack.

Battery pack capacity: 18 kWh

Cell: ANR26650M1-B

Prepare a detailed battery pack drawing along with its enclosure. State your assumptions.

3. Introduction: -

As we know that the electric vehicle market is gradually increasing. With the growth of an electric vehicle, the growth and interest in Lithium-ion cells are also increasing. The energy source for an electric vehicle is stored in cylindrical cells.

Lithium-ion cells are capable of delivering very high power. Lithium-ion cells are used in aerospace, automotive electric vehicles, mobile devices, medical devices, and other electronic devices based on these cells. The battery pack is installed on the lower floor of the electric vehicle so that weight may distribute equally and also the center of gravity also maintain properly. The high voltage battery pack is one of the most important components of any electric vehicle. The traction battery of an electric vehicle must achieve the following thing:

Provide maximum traction motor torque
Vehicle range in sense of kilometer
To achieve the proper life cycle of battery

The battery pack of an electric vehicle is generally having a series or parallel combination. Large battery packs have multiple cell modules, in which many cells are kept together to build a large battery pack. Basically, a series connection is used to compound the voltage whereas the parallel connection is for compound current capacity. A battery cell consists of five major components that are electrodes - anode and cathode, separators, terminals, electrolytes, and enclosure.

4. Mechanical design of battery pack: -

Battery packs must also be contained physically within the vehicle in such a way as to be safe in the event of crashes and during normal vehicle use and vibrations. A typical vehicle passenger zone is defined as the area between the wheel axles and inside the rocker panels on either side. Placing a battery pack outside this zone is possible, but typically requires significant structural reinforcement to be added to ensure crash integrity, adding significant cost, weight, and volume burdens to the pack. Due to the restrictive nature of volume limitations on the battery pack, the engineering of the battery packaging envelope is always a critical feature in the design of an electric vehicle. Mechanical packaging location also influences the level of robustness against water and dust intrusion which is required, with pack surfaces external to the vehicle structure requiring the greatest control. Additionally, packing location and battery chemistry type will influence whether a gas vent routing system to the vehicle exterior is necessary for the event of a cell vent during a malfunction.

5. Design consideration: -

Cell: ANR26650M1-B

6. Cell level calculation: -

Calculation as per assumptions: 18kWh Battery Pack The mathematical calculation for designing an 18kWh battery pack, basically 18kWh is the energy required to achieve the vehicle’s proper range. It is depending upon the voltage (V) parameter and ampere-hour or capacity (Ah). Here I used to design a high voltage battery pack for an electric vehicle to achieve its range up to 250 km. I assumed 145.2 V a nominal voltage for the series connection for this calculation.

General required value depending upon a single cell:

Diameter = 26 mm = 0.026m
Length = 65 mm = 0.065m
Mass = 76g = 0.076 kg
Single-cell Voltage =3.3 V
Capacity = 2.6 Ah
Max Continuous Charge Current (C - rate) = 10 A
Max Pulse Charge Current (C-rate) = 20 A

Volume of cylinder = π r^2

= x 0.0132 x 0.065

= 3.45104 x 10^-5

= 3.14 (0.026)2 * 0.065

= 0.03451 m^3

the value of the volume of the cell is used to find out the total volume of the battery pack.

Single Cell Energy (Wh)

= Cell Capacity (Ah) x Cell Voltage (V)

= 2.6 x 3.3 = 8.58 Wh

The value of a single cell is used to calculate the total energy of the battery pack.

Single Cell Energy Density

Volumetric energy (Wh/m3)

= Single Cell Energy I Volume of each cell

= 8.58 Wh / 0.03451 m3

= 248.62 Wh/m

Gravimetric energy (Wh/kg)

= Single Cell Energy / Single Cell Mass

= 8.58 Wh / 0.076 kg

= 112.89 Wh/kg

7. Battery pack calculation: -

Let's assume Nominal voltage for series connection =145.2 V, Basically, this depends upon the motor power, we can decide the value according to the motor.

Number of cells connected in series

= Nominal voltage of series connection / Nominal voltage of a single cell

= 145.2 V / 3.3 V

= 44

44 Cells will be connected in a series connection to provide a proper voltage.

Energy for battery pack (Wh)

= No. of cells connected in series x Single-cell energy

= 44 x 8.58

= 377.52 Wh

Number of cells connected in parallel

= Battery pack total energy / Energy for battery pack

= 18120.96 / 377.52

= 48

48 cells will be connected in parallel to provide a proper capacity power.

Battery pack total energy (wh) = No. of cells connected in parallel x Energy for battery pack (wh)

= 48 x 377.52

= 18120.96 wh or 18.120 kWh

Battery pack capacity

= No. of cells connected in parallel x Single cell capacity (Ah)

= 48 x 2.6 Ah

= 124.8 Ah

The value of battery pack capacity is used for the total power required by the vehicle.

Total number of cells for battery pack

= No. of cells connected in parallel x No. of cells connected in series

= 48 x 44

= 2112

Cells will be used to make a complete battery pack.

Mass of the battery pack

= Total no. of cells for batter pack x Mass of single-cell

= 2112 x 0.076 kg

= 160.512 kg

It is the total weight of cells connected in parallel or series.

Total volume of the battery pack

= Total no. of cells for batter pack x Volume of single cell

= 2112 x 0.0345

= 72.89 m^3

This is the volume of 2112 cells that are used in the battery pack system.

Cell peak current (A)

= Crate (Max Pulse Charge Current) x Single cell capacity

= 20 x 2.6

= 52 A

Battery pack peak current (A)

= Cell peak current x No. of cells connected in parallel

= 52 x 48

= 2496 A

It is used for the operation of the battery pack. In this way, a vehicle will decide how much power is required to move.

Battery pack peak power (W)

= Battery pack peak current x Voltage of series connection

= 2496 A x 145.2

= 362419.2 or 362.42 W

Cell continuous current (A)

= C-rate (Max Continuous Charge Current) x Single cell capacity

= 10 x 2.6

= 26 A

Battery pack continuous current (A)

= Cell continuous current x No. of cells connected in parallel

= 26 x 48

= 1248 A

This is the power which is supply continue to the whole battery pack system.

Battery pack continuous power (W)

= Battery pack continuous current x Voltage of series connection

= 1248 x 145.2

= 18120.96 or 18.120 kWh

The above calculation is to find the total number of cells for a full battery pack for an Electric vehicle, also the battery pack weight, current, capacity, and voltage. For design purposes and easy installation here, I configure this large battery pack into a small module. the small modules consist of 32 cells into 66 modules and every single module will have 8S / 4P.

8. Battery pack dimensions: -

Length of casing (L) = number of cells x (cell diameter + margin at both side of cells) + clearance at side L

= 44 x (26 + 4) + 60

= 1380 mm

Breadth of the casing (B) Breadth = number of cells x (cell diameter + margin at both side of cell) + clearance at side B

= 48 x (26 +4) + 60

= 1500 mm

Height of casing (H)-Height = Height of cell + margin for wiring H

= 65+35

= 100 mm

9. The final battery pack assembly: -

9.1 Arrangement and assembly of 8S/4P module with 32 cells.

The detailed technical specification of the module is as follow:

Package: 8S/4P
Capacity: 10.4 Ah
Voltage: 26.4 V
Weight:2.432 kg (Only Cells)
Power: 274.56 Wh

9.2 Assembly of the full battery pack with 44S / 48P.

Battery module: - 32 cells with 8S / 4P 32 cells x 66 pack = 2112 cells. 2112 cells will have 44S / 48P Here I arrange the pack such that it will build a proper battery pack. That is 32 modules of 8S4P. The detailed technical specification of the battery pack is as follow:

Package: 44S / 48P
Capacity: 124.8 Ah
Voltage: 145.2 V
Weight: 160.512 kg (Only Cells)
Power:18120.96 Wh or 18.12 kWh

Battery Calculation	Value	Unit
Single Cell Calculation
The volume of a single cell	0.03451	M^3
Single Cell Energy	8.58	Wh
Single Cell Energy Density Volumetric energy Gravimetric energy	248.62 112. 89	Wh/m^3 Wh/kg
Calculation of High Voltage Battery Pack for 18 kWh
Average energy	72.483	Wh/km
Nominal voltage for series connection	145.2	V
Number of cells connected in series	44
Energy for battery pack	377.52	wh
Number of cells connected in parallel	48
Battery pack capacity	124.8	Ah
Total number of cells for battery pack	2112
Mass of battery pack	167.2	kg
The total volume of the battery pack	73.89	m^3
Cell peak current	52	A
Battery pack peak current	2496	A
Battery pack peak power	362.42	kw
Cell continuous current	26	A
Battery pack continuous current	1248	A
Volume of cell	0.03451	m^3
Volume of battery pack	72.8851	m^3

10. The main parts in battery pack design; -

11. Mechanical testing: -

12. Standard for the battery: -

13. Comparison of structural characteristics of different types of battery cells: -

14. Assembly and Testing line for battery pack: -

15. Conclusion: -

From the single-cell technical data here I have designed a battery pack for the electric vehicle which is having total energy of 18.121 kWh or 18 kWh. The total number of cells is 2112 which are in the configuration of 44S / 48P. Also, the nominal voltage from the 44 series connection of the battery gives 145.2 V and the capacity power we get from the arrangement of 48 parallel cells is 124.8 Ah.

All design is used to achieve a 250 km range by the vehicle, which is an assumption to calculate the battery pack. Here if I will increase the number of cells in parallel then the power will increase but at that time the distance will not be achieved by the vehicle, that's why here I use 44S / 48P cell configuration for the battery pack. Also, the whole battery pack is subdivided into 66 packs in which each block has 32 cells and this configuration is prepared to set up 44S / 48P cell configuration.

16. References: -

Project 1 Mechanical design of battery pack

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