Project 1 Mechanical design of battery pack

From the datasheet and it is attached

Nominal Voltage: 3.3 V

Cell Capacity: 2.5 Ah

Internal Impedance: 6m ohms

Cell weight: 76 g

Cell dimension = 26*65 mm

Operating Temperature = -30 to 55 ⁰C

Depth of discharge characteristics of a cell form the datasheet

• Total no of Cells = Energy/ (nominal voltage * Capacity)

= 18000/ (3.3*2.5) =2182 cells

We need around 2182 cells for 18 KWh, battery pack capacity

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

• No of series cells = Required Voltage/Nominal Voltage

=500/3.3

= 151.51

Let’s assume the total no of series cells as 152

• Total cells = no of series * no of parallel

No of parallel = 2182/152= 14.35

Let’s assume the total no of parallel cells as 15

Now the cell architecture is 152s15p

• 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*26m = 3.95 m
• Width = No of parallel*diameter = 15*26m = 0.39 m
• Height = 65mm
• Area required for 152s15p = 2(Length + Width) *Height

= 2(3.95+0.39) *65m

= 0.564 m²

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

=2182*76

= 165.83 kgs

The battery given is a cylindrical battery so we will use cells holders to make 152s15p architecture and spot welding for the connections in the battery pack.

Exterior stability design and module of a battery pack

Various Interface in battery pack

Interface	Remarks	Solutions
· Mechanical	Design features for safety	Cell spacers, damping pads, gaskets etc
· Structural	Protection and isolation	Case, cover, end plates etc
· Thermal	To maintain cell temperature	Coolant, fans, heat exchange etc
· Electrical	Transmits power from and to battery pack	Bus bars, relays, fuse etc
· Control	To monitor and regulate the battery pack	BMS, various sensors

To maintain the temperature within the battery pack the coolant flow

Battery Module with BMS

Characterisation of the impact during performance :

• Customer Usage : The driving range of an 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 from

battery packs.

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

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