Project 1 Mechanical design of battery pack
Preparing a battery pack using cell: ANR26650M1-B
CAPACITY:18KWh.
cell details and specifications
ANR26650M1-B is a Nano phosphate High power Li-ion cell.
The dimensions of the cell are from the name we can find. that is 26 represents the diameter and 65 represents the height and 0 represents the cylindrical structure.
The Nominal voltage of the cell is 3.3volts.
The capacity of the cell is 2.5Ah.
To make a battery pack of 18KWh capacity , we need to design the cell configuration
we knew in series connection of cells , the voltages all added up together.
and in parallel configuration of cells , the currents will added up.
In the above image ,
each cell having 1.5 volts connected in parallel have the same voltage,
but in series connection of same cells we are getting 6volts.
the currents in series connections are equal.
based on the above knowledge we are able to design the configuration of the battery pack of 18KWh.
here we already know the cell voltage 3.3 volts and each cell capacity is 2.5 Ah .
capacity = voltage * current * time
18,000wh = 3.3(x) * (ampere* hour)y
18,000Wh= 3.3(x) * 2.5(y)-----------(i)
here x and y are variables which represents no.of series and parallel connections
x = no of series connections
y = no of parallel connections
Here 3.3(x) determines the battery pack voltage, and 2.5(y) represents the Ah capacity
Assuming the Batterypack voltage to be 363volts.
so , 3.3(x)=363volts
x=110 ; The no.of series connections are 110
it means 110 cells are connected in series.
from equation(i)
2.5(y)=18,000/363
y=20; The no.of parallel connections are 20
The total no. of cells are 110*20=2200 cells.
Estimation of Total Battery pack Capacity:
we know the Ah capacity depends on the no.of parallel legs of the battery pack.
here 110 cells are connected in series forming a group.
and such groups of 20 are connected in parallel.
so amp hour capacity increased by 20 times.
The total amp hour capacity of the battery is = 20*2.5Ah= 50Ah.
for electric vehicle battery pack cell are connected in series and parallel configuration and then stacked to form a module . again these modules are connected in a series parallel fashion according to the required voltage and capacity of the battery pack.
Finally all these modules are stacked together to form the Battery pack.
Estimation of the volume of the Battery pack:
Assuming cube structure of the battery for better calculation of the volume , To account for the gaps between the cells.
That is why we are not calculating the cylindrical volume.
height =65mm
and width =26mm
volume =65*26*26 mm^3
volume=43940mm^3.
for 2200 cells , the estimated volume of the batterypack is 2200*43940mm^3=0.09666m^3.
Estimation of Energy Density:
energy density is energy per unit volume .
energy of one cell is voltage * current*time= 3.3v *2.5Ah= 8.25Wh
so we are getting 8.25Wh energy from the volume of 0.09666m^3.
for 1m^3 we get the energy of,
energy density =8.25/0.09666 =85.3wh/m3
Estimation of Total weight:
each cell weight is 76grams
so 2200 cells contains a minimum weight of 2200*76g=167.2kg
packaging and assembly of the cells:
There is a proper sequence involved to package and assembling the cells into a batterypack.
To account for the safety and vibration effects and insulation and etc.
we connect cells positive and negative terminals to other cells using nickel material.
we are having different styles of nickel strips according to the size of the cell.
different cell dimensions and their configuration of series and parallel connection decides the
style of nickel strip to be used.
The following figures shows the nickel metal strips for 26650 model cells
Spot welding:
spot welding is a process to connect the nickel metal strips to the battery terminals.
we are not advised to use soldering because the heat developed from the soldering operation may decrease the life of the batteries.
The Design of Encloser:
An encloser is something that stores the whole batterypack,
It has to incorporate battery pack and the battery management system and vents and provide good insulation properties and encounter unwanted surrounding changes like temperature and rain and accidents.
An encloser should support for the mechanical vibrations , thus cells and the connections inside the batteries should not be disturbed.
References:
https://link.springer.com/article/10.1007/s00158-018-1901-y
http://micahmartin.com/eflight/2018/08/06/welding-batteries.html
https://www.compositesworld.com/articles/ev-battery-enclosure-inspires-material-process-innovations