Project 1 Mechanical design of battery pack

Mechanical design of battery pack

Aim

Design a battery pack of 18 kWh with ANR26650M1-B cell.

Objective

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

Mechanical design of battery pack

In an electric vehicle (EV), thermal runaway, vibration or vehicle impact can lead to a potential failure of lithium-ion (Li-ion) battery packs due to their high sensitivity to ambient temperature, pressure and dynamic mechanical loads. Amongst several factors, safety and reliability of battery packs present the highest challenges to large scale electrification of public and private transportation sectors.

For designing the 18kWh battery pack we are using cell model ANR26650M1-B. These cells uses lithium iron phosphate (LiFePO4) batterytechnology delivers high power and energy density combined with excellent safety performance and extensive life cycling in a lighter weight, more compact package. Our cells have low capacity loss and impedance growth over time as well as high usable energy over a wide state of charge (SOC) range, allowing our systems to meet end-of-life power and energy requirements with minimal pack oversizing.

Technical Data of cell - ANR26650M1-B

Mathematical Designing of Battey Pack

Power of Battery Pack, E = 18 kWh = 18000 Wh

Nominal Voltage, Nv = 3.3 V

- Assume Battery Pack Voltage, Bv= 400 V

• Total no: of cells conncted in series, Ts = Assume Battery Pack Voltage (Bv) / Nominal Voltage (Nv)

= 400 /3.3

= 122 cells in Series

Cell Capacity, Cc = 2.5 Ah

• Capacity of Battery Pack, Cp = Power of Battery Pack (E) / Assume Battery Pack Voltage (Bv)

= 18000 / 400

= 45Ah

• Total no: of cells conncted in parallel, Tp = Capacity of Battery Pack (Cp) / Cell Capacity (Cc)

= 45 / 2.5

= 18 cells in Parallel

• Total no: of cells, Tt = cells conncted in series (Ts) x cells conncted in parallel (Tp)

= 122 x 18

= 2196 Cells

18 kWh 45 Ah Battery pack can be designed with 122S18P configuration

Cell Weight, Cw = 76 g

• Total Weight of the Battery Pack, Tw = Total no: of cells, Tt x Cell Weight, Cw

= 2196 x 76

= 167 Kg (Approx)

Cell Length, Cl = 65 mm = 0.065 m

Cell Diameter, Cd = 26 mm = 0.026 m

• Length of the battery pack, Lp = Cell Diameter, Cd x Total no: of cells conncted in series, Ts

= 0.026 x 122

= 3.17 m (Approx)

• Widgth of the battery pack, Wp = Cell Diameter, Cd x Total no: of cells conncted in parallel, Tp

= 0.026 x 18

= 0.49 m (Approx)

• Area of the Battery Pack, Ap = Length of the battery pack, Lp x Widgth of the battery pack, Wp

= 3.17 x 0.49

= 1.56 m^2 (Approx)

• Volume of the Battery Pack, Vp = Area of the Battery Pack, Ap x Cell Length, Cl

= 1.56 x 0.065

= 0.102 m^3 (Approx)

• Specific Energy Density, Es = Power of Battery Pack, E / Total Weight of the Battery Pack, Tw

= 18000 / 167

= 107.8 Wh/kg(Approx)

• Volumeteric Energy Density, Ev = Power of Battery Pack, E / Volume of the Battery Pack, Vp

= 18000 / (0.102 x 1000)

= 176.5 Wh/L (Approx)

Arrangement of 122S18P configuration Battery pack

10S3P configuration battery pack

Other Parts required for the designing of a battery pack

• Cell Holder

• Cell Connecting Nickel Strip

• Battery Management System (BMS)

Battery management system (BMS) is technology dedicated to the oversight of a battery pack, which is an assembly of battery cells, electrically organized in a row x column matrix configuration to enable delivery of targeted range of voltage and current for a duration of time against expected load scenarios. The oversight that a BMS provides usually includes:

• Monitoring the battery
• Providing battery protection
• Estimating the battery’s operational state
• Continually optimizing battery performance
• Reporting operational status to external devices

• Solder/Weld

Most battery packs are spot welded together using nickel strip for contacts. Soldering directly to the cells is dangerous for the cells. It is easy to melt or disturb the safety vent, thwack the seals, or cause internal shorting if the heat is too high. This damage might not be noticeable until later.

• Enclosure/Cases/Cainets

The most common battery enclosures are made from plastic materials that are resistant to alkaline solutions and have a high impact strength. Metal housings are sometimes used, but metal requires careful design and assembly to avoid shorting of the cells in the battery pack.

Conclusion

The mathematical design of battery pack has been carried out and calculted the the data required for the designing process. - The design consists of 122S18P configuration battery pack with a total of 2196 cells of ANR26650M1-B with a total energy 18kWh.

- The battery pack has a dimension of length 3170 mm and width 490 mm, with a total area of approximately 1.56 m^2.