Project 1 Mechanical design of battery pack

Project 1 Mechanical design of battery pack

Battery pack capacity: 18 kWh

Cell: ANR26650M1-B

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

Basic definitions:

Battery :- A battery is a device that stores and provides electrical energy through a chemical reaction.

Battery module:- A battery module is a structured assembly of individual battery cells designed to work together within a larger battery system or battery pack.

Battery pack:- A battery pack is a collection of individual batteries or cells that are interconnected and housed within a single unit. The purpose of a battery pack is to provide a higher combined voltage, capacity, and energy storage than what a single individual battery cell can offer.

Battery Holders or Casings:- Battery cells are typically enclosed in holders, casings, or modules to protect them from physical damage and to provide a structured form factor for the battery pack.

Enclosure or Housing:- An outer protective casing or housing is often used to contain and safeguard the battery pack.

Solution:

The mechanical design of a battery pack involves the physical structure, layout, and enclosure of the battery assembly. Several key considerations and components are required for a well-designed battery pack, some are listed below:

ü Battery Module/Cell Arrangement

ü Enclosure or Housing

ü Mounting and Fastening

ü Thermal Management

ü Ventilation

ü Seals and Gaskets

ü Wiring and Cable Routing

ü Shock and Vibration Isolation

ü Compliance with Standards

ü Material Selection

ü Testing and Validation

Battery pack is designed to meet the below requirements:

Battery pack capacity, E_bp: 18 kWh

Battery pack voltage, U_bp: 320V

Cell used: ANR26650M1-B

Cell voltage: 3.3V

Cell capcacity: 2.5Ah

Cell (ANR26650M1-B) datasheet:

PROCEDURE FOR THE CALCULATIONS:

1. Volume of each cell

Cylindrical volume V_c [m³]

Diameter of cell, D_c = 26mm = 0.026m I.e. r = 0.013m

Length of cell, L_c = 65mm = 0.065m

V_c = πr² × h

V_c = π. 0.013² × 0.065

Volume of cell, V_c = 3.45 × 10⁻⁵ m³

2. Battery Cell Energy

Capacity of cell, C_c = 2.5Ah

Voltage of cell, U_c = 3.3V

E_c = C_c . U_c

E_c = 2.5 x 3.3

Energy of cell, E_c = 8.25 Wh

3. Battery cell energy density

l Volumetric energy density

l Gravimetric energy density

4. Total energy of the battery pack

The total energy of the battery pack which is required is given as 18 kWh

E_bp = 18000 Wh

5. Number of cells connected in series

It is calculated by dividing the nominal battery pack voltage U_bp [V] by the voltage of each battery cell V_c [V]. The number of strings must be an integer. Therefore, the result of the calculation is rounded to the higher integer.

Let us assume that the battery pack voltage which is required to be 320V and the nominal voltage of the battery as per the data sheet is given as 3.3V.

The total number of cells in series is 97.

6. Energy Content of a string

The product between the number of battery cells connected in series and the energy of a battery cell.

E_bs = N_{cs .} E_c = 97 x 8.25 = 800.25 Wh

7. Number of strings in the battery pack

It is calculated by dividing the battery pack's total energy E_bp [Wh] by the energy content of a string E_bs [Wh]. The number of strings must be an integer. Therefore, the result of the calculation is rounded to the higher integer.

All the 23 strings will be connected in parallel.

8. Battery pack Capacity

It is calculated as the product between the number of strings N_sb [-] and the capacity of the battery cell C_c [Ah].

C_bp = N_sb . C_c = 23 x 2.5 = 57.5 Ah

9. Total number of cells of the battery pack

It is calculated as the product between the number of strings N_sb [-] and the number of cells in a string N_cs [-].

N_cb = N_sb . N_cs = 23 x 96.96 = 2230.08

The total number of cells required for the design pack is 2230.

10. Mass of the battery pack

It is the product of the total number of cells N_cb [-] and the mass of each battery cell M_c [kg].

M_bp = N_cb x M_c = 2230 x 0.076 = 169.48 kg.

11. Volume of the battery pack

It is the product of the total number of cells N_cb [-] and the mass of each battery cell M_c [m3]. This volume is only used to estimate the final volume of the battery pack since it does not take into account the auxiliary components/systems of the battery.

Vbp = N_cb x V_c = 2230 x 3.45 × 10⁻⁵ = 0.0769 m³

^{Battery dimensions-}

^{1. Length of casing (L)}

^{length = number of cells x (cell diameter + margin at both side of cells ) + clearance at side}

^{L = 97 x (26 + 1.5 + 1.5) + 60 = 2873 mm = 2875mm (rounded to nearest round number for easy manufacturing)}

^{2. Breadth of the casing (B)}

^{Breadth = number of cells x (cell diameter + margin at both side of cell) + clearance at side}

^{B = 23 x (26 + 1.5 + 1.5) + 60 = 727 mm = 730mm (rounded to nearest round number for easy manufacturing)}

^{3. Height of casing (H)}

^{Height = Height of cell + margin for wiring}

^{H = 65 + 45 = 110 mm}

^{Assembly process of the battery pack}

^{Coomponents required:}

Ø ^{Battery Cells: These are the individual cells that store electrical energy. Ensure they are of the same type and specifications to create a consistent pack.}

Ø ^{Battery Holder: The battery holder or frame is used to securely arrange and hold the battery cells in place within the pack.}

Ø ^{Spot Welding Equipment: Spot welding is a method used to create strong and precise electrical connections between the battery cells, nickel strips, and other components. You'll need a spot welding machine.}

Ø ^{Safety Components: These components include safety features like fuses and a protection circuit board (PCB) to protect the battery from overcharging, over-discharging, and other faults.}

Ø ^{Insulator: Insulating materials are used to separate the battery cells and prevent electrical shorts. They can be placed between cells and around connections.}

Ø ^{Cooling Plate/Heat Sink: A cooling plate or heat sink helps regulate the temperature of the battery pack, dissipating heat to prevent overheating.}

Battery with battery holder

Battery with insulator

Nickel strip

^{The assembly process of a battery pack involves several critical steps to create a functional and safe power source. It begins by carefully arranging battery cells within a battery holder or frame. These cells are then interconnected using spot welding equipment, creating strong and precise connections through nickel strips. Safety components like fuses and protection circuit boards (PCBs) are installed to safeguard against overcharging, over-discharging, and short circuits. Insulating materials are used to prevent electrical shorts, and if required, a cooling plate or heat sink is added for temperature regulation. The assembly is tested to ensure proper electrical connections and safety measures, and the final battery pack is labeled with important information such as voltage and safety warnings. Quality control measures are taken to verify the functionality and safety of the assembled battery pack.}

^Conclusion:

^{Number of cells in parallel = 23}

^{Number of cells in series = 97}

^{Total number of cell = 2230}

^{Size of enclosure = 2875 (L) x 730 (B) x 110 (H)}

^{Designed value of Battery pack voltage = 320 V}

^{Designed value of Battery pack capacity = 18 KWh}

^{Mass of battery pack = 170 kg}

^{The mechanical design of a battery pack is a critical process that encompasses a range of considerations to ensure the safe and efficient operation of the battery system. Key factors in this design include the selection of appropriate battery cells, the arrangement of cells in series and parallel configurations to achieve the desired voltage and capacity, and the integration of safety features like thermal management components, safety disconnects, and secure enclosures. Attention to detail in the mechanical design, such as providing adequate clearances, insulation, and secure fastening of components, is crucial for preventing hazards and ensuring reliability. Furthermore, adherence to safety standards and thorough testing and quality control measures are essential to verify the integrity and functionality of the battery pack. Successful mechanical design balances performance and safety, making it suitable for various applications, from portable devices to electric vehicles and renewable energy storage systems. Collaboration with experienced professionals and compliance with relevant regulations are essential for a successful battery pack mechanical design.}