Project 1 Mechanical design of battery pack
BATTERY PACK DESIGNING :
Cell: ANR26650M1-B :
A123’s high-performance Nanophosphate lithium iron phosphate (LiFePO4) battery technology 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 .
The data sheet for the above cell is given below ;
Diffrent characteristics of the cell are shown below :
18 kWh CAPACITY BATTERY PACK CONSTRUCTION :
The battery pack consists of diffrent comoonents like cells modules and cooling arrangement and all.
The battery pack is formed by secondary cells due to they are rechargable.
The arrangement or group of cells in an order is known as module .
The group of modules forms the battery pack.
The above cell has the specifications of nominal voltage (V)=3.3V
Cell capacity(Ah) =2.5Ah
Cell energy (E) =3.3*2.5 =8.25kwh .
We need to build 18kwh capacity battery pack .
let us assume the vehicle motor has the voltage rating of 120V .
Then the battery pack should have the same voltage rating to satisfy the load .ie, 120V.
The battery pack current rating (capacity )is given by Energy / votage
capacity (ah ) = 18000 /120 = 150Ah capacity .
Let us assume from the modules level ;
One module has 5S3P ie, 5 series and 3 parallel cells
5series cells voltage = 3.3*5= 16.5V
3parallel cells capcity=2.5*3=7.5Ah
so, 5S3P module can provide 16.5V and 7.5Ah.
5S3P provides 123.75 wh capacity .
So The no of 5S3P modules reiquire to provide 18000wh is given by
18000/123.75 =145.45 similar to 146 modules .
Cells for 1 module is 5*3 = 15 cells .
Total no cells required to form the battery pack are 15*146 =2190 cells.
WE can get 18067.5wh from the 123.75 kwh *146 modules
The remaing we will consider as losses .
Another thing is we can't get exact 18kwh if we arrange them theritically calculations due to their internal connection resistance and losses also.
MECHANICAL DESIGN OF THE BATTERY :
The mechanical battery Construction involves diffrent processes and components also like;
1.CELL SELECTION :
The first step is to select cell based on our requirement .
The cells should be secondary only . due to they are rechargable.
The cells have diffrent chemistries and all with diffrent energy density power density and all.
2.CELL HOLDERS :
The cell holders holds or mount the cells in them.
The no of cells to form the modules and modules form the battery pack by using the cell holders .
These holders are avilable in different shapes like recatangle ,hexgonal also
Molded plastic type holders are preferd mostly.
3.ELECTEICAL CONNECTIONS OF CELLS :
The battery pack consists of many cells in series & parallel so these should be properly conected electrically.
Before connecting them in parallel or series all cells are tested for voltage and currents for performance.
The connections should be Without any short circuits & loose connections .
If any loose connections cells may get heated up and damae the entire battery pack.
The mostly used elctrical connections welded by the conducting materials.
Spot welding techinique is used to connect the battery terminals.
Another type of electrical connections are there like lego connectors .
The lego connectors are like cell holders with electrical connections .
We can connect & dissconect the cells simply by connecting these connectors.
Nickel strips :
4. BMS - BATTERY MANAGEMMENT SYSTEM :
Battery Management System (BMS) is an intelligent component of a battery pack responsible for advanced monitoring and management.
It is the brain behind the battery and plays a critical role in its levels of safety, performance, charge rates, and longevity.
It is emmbeded system ie , software and hardware components .
Hardware takes care for electricals of battery pack .
Software coordinates with the user and battery .
It monitors and controll the voltage , current , temperature of the battery every time .
Give the SOC information of the battery.
It controlls the charging and discharging of the battery .
The cell balancing is also provided by the BMS of the battery.
It improves the performance of the battery.
4.FINAL ASSEMBLY OR ENCLOSURE :
The final assembly is last process in this all components are arranged properly .
Before that a cells volatge and currents are measured for the balancing condition .
It includes master level BMS for the entire battery pack .
The below image represents the assembling of the battery battery pack.
