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.

From Datasheet,

Nominal Voltage = 3.3 V

Cell Capacity = 2.5 Ah

Internal Impedance = 6 m ohms

Cell Weight = 76 g

Cell Dimension = 26*65 mm

Operating Temperature = -30 to`55^0`C

Depth of discharge characteristic of a cell from datasheet :

• Total No. of Cells = Energy / (norminal voltage * Capacity)

= 18000 / (3.3 * 2.5)

= 2128 cells

We need around 2128 cells for 18kWh, battery Pack capacity

Let's assume battery pack voltage required for 18kWh is around 500 V

• No. of Series Cells = Required Voltage / Nominal Voltage

= 500 / 3.3

= 151.51

Let's assume the total no of sreies cells as 152.

• Total Cells = No. of Series / No. of Parallel

No. of Parallel = 2128 / 152 = 14.35

Let's assume the total no of parallel cells as 15.

Now the cell architecture is 152 series 15 parallel.

• Rated Capacity of Battery Pack = 15 * 2.5 = 37.5 Ah.
• After assumptions, the total battery pack capacity = (152 * 3.3) * (15 * 2.5) = 18.81 kWh.
• Length = No. of Series * Diameter = 152 * 26 = 3.95 m.
• Width = No. of Parallel * Diameter = 15 * 26 = 0.39 m.
• Height = 65 mm.
• Area required for 152 series 15 parallel = 2 (Length + Width) * Height

= 2 (3.95 + 0.39) * 65

= 0.564 `m^2`

• Total Weight of battery pack = Total cells * Each cell weight

= 2128 * 76

= 165.83 kgs

The battery given is a cylinderical battery so we will use cells holders to make 152 series and 15 parallel architectur and spot welding for connections in the battery pack.

Exterior Stability design and module of an battery pack

Various Interface in Battery pack

Interface	Remarks	Solutions
Mechanical	Design features for safety	Cell spacers, damping pads, gaskets and etc.,
Structural	Protection and isolation	Case, Cover, end plastes etc.,
Thermal	To maintain cell temperature	Coolant, fans, heat exchanger, etc.,
Electrical	Transmits power from and to battery pack	Bus bars,relays, fuse, etc.,
Control	To monitor and reguiate the battery pack	BMS, Various sensors

To maintain the temperature within battery pack coolant flow

Battery Module With BMS :

Characterisation of impact during performance :

• Customer Usage : The driving range on EV depends on the speed and acceleration characteristics of each trip.Trips with faster acceleration or including ascents over high altitude grades demand more kilowatts per kilometre travelled. Moreover, studies of the driving patterns of EVs indicate that, unlike conventional ICE vehicles, EVs are rarely driven under high-speed motorway conditions and more in rural and urban environments. Consequently, battery packs of EVs that are driven mainly on rural or urban terrain are exposed to a more strenuous life in comparison to those driven over more traditional compositions of road surfaces.
• Vibrations : Driving induces vibration profiles concentrated in the 1 Hz - 25 Hz frequency range with as much as 10% higher energy levels. Pouch cells, which are more common in EV applications, are more prone to localization of vibrational forces. This can in turn cause sharp increases in local stress levels in battery packs, resulting in mechanical and electromechanical failure.
• Ambient Temperature : Another factor that can have a significant effect on the available energy and cycle life of Li-ion batteries is the battery cell temperature. It has been found that with each degree increase in battery cell temperature in the operating range of 30 °C and 40 °C, the cycle life of batteries is reduced by approximately two months Moreover, an estimate by General Motors indicates that an EV can lose up to 85% of its range at sub-zero temperature if no thermal management system is used. In addition, the rate of self-discharge is also dependent on the storage temperature. The energy capacity of a battery also degrades in response to the ambient temperature and other factors throughout its cycle life.
• Cell-to-Cell Variations : Accidental and practically unavoidable physical and chemical variations among battery cells have a far-reaching effect on the structural dynamics of the battery pack. These random variations lead to the confinement of vibrational energy to a small portion of the cell structure. It is therefore vital to minimise any random cell-to-cell variations in order to define battery performance reliably, as each battery cell will react in a peculiar manner to stimuli received from other sources of disturbance, such as customer usage or the external environment.
• Auxiliary Load : System interactions, such as heat leakage from different electromechanical systems, chassis
  vibrations, electrical interference, and auxiliary loads like cabin heating/cooling, power steering and air compressors affect the quality of output frombattery packs.

Even the below factors have to be considered while designing the battery pack

• Lightweight
• Compactly packaged
• Ergonomic
• Structurally rigid
• Swappable
• Configurable and scalable
• Thermallv stable
• Impact-resistant
• Fire-proof
• Easy to manufacture
• Easy to service
• Low-cost.