Project 1 Mechanical design of battery pack

Objective: To prepare a detailed battery pack drawing along with its enclosure.

Battery pack capacity:18kwh

Cell: ANR26650M1-B

Nanophosphate Technology 26650 Lithium-Ion power cell

Key features and benefits of Nanophosphate high power Lithium-Ion cell ANR26650M1-B

• excellent abuse tolerance and superior life cycle from A123's patented nano phosphate lithium-ion chemistry.
• high power with over 2,600W/kg and 5,800 W/L, 10 sec, 50% SOC.
• high useable energy over a wide state of charge range.

Specs of ANR26650M1-B

Dimensions

Nanophospahte battery technology offers stable chemistry, faster charging, consistent output, excellent cycle life and superior cost performance. it provides the foundation for safe systems while meeting the most demanding customer requirements. multiple layers of protection are employed at the chemistry, cell and system level to achieve an energy storage solution with superior safety and abuse tolerance compared to metal oxide lithium-ion chemistries.

Applications

commercial solutions

advanced lead-acid replacement batteries for

• datacentre UPS
• telecom backup
• IT backup
• autonomously guided vehicles [AGVs]

government solutions

• military vehicles
• military power grids
• directed energy

Grid Solutions

• frequency regulation
• renewable energy integration
• reserve capacity
• transmission and distribution

Transportation Solutions

• commercial vehicles
• off-highway vehicles
• passenger vehicles

Battery Pack(definition)

a battery pack is a set of any number of (preferably) identical batteries or individual battery cells. they may be configured in a series, parallel, or mixture of both to deliver the desired voltage, capacity or power density. components of a battery pack include the individual batteries or cells, and the interconnects which provide electrical conductivity between them. rechargeable battery packs often contain a temperature sensor, which the battery charger uses to detect the end of charging.

figure: images of battery pack

Stages of Battery Pack Design

Cell configuration

series batteries:

the positive terminal of one cell is connected to the negative terminal of the succeeding cell to achieve a series connection. the series configuration is used where the voltage of a single cell is not sufficient. the series configuration is achieved by connecting the positive of a cell to the negative of another cell. in series configuration capacity remains the same and voltage will be the sum of individual cell voltage.

parallel configuration

here the positive terminals of the cells are connected together, similarly, negative terminals are connected together in order to achieve parallel connection. the cells are connected in parallel to fulfill higher current capacity requirements if the device needs a higher current but there is not enough space available for the battery. that device can use the parallel configuration to fit high-current capability in a small space.in this configuration, the voltage remains the same and capacity accumulates.

series-parallel configuration/mixture of series and parallel battery cells

in this configuration, the cells are connected in both series and parallel. the series-parallel configuration can give desired voltage and capacity in the smallest possible size.

design elements to be considered while designing a battery pack

Battery Management System

electrical vehicles run on rechargeable battery packs that are made of multiple cell modules arranged in series and parallel. these battery packs produce several hundred volts of electricity. various functions inside the car are dependent on them. that is why it becomes a critical component of the vehicle that requires constant monitoring and control. this requires Battery Management System(BMS) an embedded system, which monitors the components closer to the battery cell as each cell needs to be closely monitored so that there is no voltage fluctuations or imbalance in voltage conditions.

the main function of BMS is to ensure that the battery is protected and any operation out of its safety limit is prevented. it monitors the battery packs state of charge along with its state of health. BMS also manages the battery optimistaion via cell balancing that improves the life of the battery in the long run. the BMS will also monitor the voltage, different temperature parameters and coolant flow.

Battery Pack Construction

connection system

• the connection system transforms cells into a battery pack.
• the bms and battery pack must be interfaced with each other .
• nickel strips are the preferred method for connecting battery pack to the control system. these strips are capable of carrying high amount of current , they are flexible, durable and can be attached to cell with using excessive heat.

battery pack casing/ housing

battery housing consists of actual stainless steel housing, which creates the structural load capacity between the components, batteries and control components in the interior. housing ensures that the components remain safely located and provides clean package for the eventual use of by the consumers.the type of housing depends on where the battery pack is installed .

Thermal design

thermal management is a major issue in high power designs, particularly for automotive applications. as part of the battery system, it may be necessary to provide air or water cooling ducts, pumps or fans and heat exchangers for high temperature working or heaters for operating low-temperature environment. the layout of the cells should be conducive to managing heat flows within the pack.

Electrical Distribution System

Battery pack assembly line

Mechanical Design Process

Cell parameters used for mechanical design:

cell voltage=3.3V battery pack capacity= 18kwh(given)

cell capacity=2.5 Ah

cell weight =76g

cell diameter=25.96mm

cell height=65mm

cost of each cell=$6.55

Calculations

let pack voltage = 400V

pack capacity= energy capacity/ pack voltage

=18000/400= 45Ah

in a series configuration, capacity remains the same and voltage will be the sum of individual cell voltage

No. of cells in series

Ns= pack voltage/cell voltage=400/3.3=121.2

Ns=122 cells(approx.)

in a parallel configuration, the voltage remains the same, and capacity accumulates

no. of cells in parallel

Np=pack capacity/cell capacity= 45/2.5

Np=18 cells

total number of cells in battery pack

= no. of cells in series * no. of cells in parallel

=Ns * Np

=122*18

=2196 cells

weight of the battery pack

cell weight=76g=0.076kg

weight of battery pack= total no. of cells in battery pack * cell weight

=2196 * 0.076kg

=166.896

=167kg(approx.)

length of the battery pack

no. of cells in series * cell diameter

=122 * 0.026

=3.172m

Width of the battery pack

no. of cells in parallel * cell diameter

= 18 * 0.026

=0.468 m

Area of the battery pack

area = length * width

= 3.172 * 0.468

= 1.4845 m^2

Volume of the battery pack

volume= length * widht * height

= 1.486 *0.065

=0.0965m^3

=96.5 litres

specific energy density

= pack energy capacity/weight of battery pack

=18000/167= 107.784Wh/kg

Volumetric Energy Density

= pack energy capacity/volume

=18000/96.5= 186.53Wh/litre

Cost of the battery pack

cost of each cell=$6.55 = Rs 490.78

cost of battery pack= total no. of cells * cost of each cell

=2196 * 490.78

=Rs 10,77,796.8/-