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.
Aim: To design a battery pack capacity of 18KWh using a cells of ANR26650M1-B and discuss steps involved in designing a battey pack.
Cell:ANR26650M1-B
A123's high - performance Nanophosphate lithium iron phosphate ( LiFePO4 ) battery technology delivers high power.
The energy density combined with excellent safety performance and extensive life cycling in a lighter weight , more compact package.
cells have low capacity loss and impedance growth over time as well as high usable energy over a wide state of charge ( SOC ) range These allows the systems to meet end-of-life power and energy quirements with minimal pack oversizing.
Data sheet of cell ANR26650M1-B
Electrical Configuration
Single cell has voltage of 3.3V and 2.56Ah of ratings.
Capacity of single cell=3.3V * 2.56Ah = 8.448 watt hour
Assuming Battery pack voltage of 330V.
Series connection of cells:
Each cell voltage is 3.3V and pack voltage should be 330 Volt, therfore 100 cells are needed to be connected in series.
Ns=330/3.3=100 cells.
Parellel connection of cells
Required capacity is 18000wh
As voltage is assumed to be 330 V
Therfore current output at terminals of battery pack is 18000/330=54.54Ah
Single parallel path produces 2.56Ah,
therfore Total Number of cells are: 54.54/2.56=21.3=22 ( approximately ) parallel connections are required.
Total Number of cells are:
Number of cells in series mulipiled by number of cells in parallel=100*22=2200 cells are required.
Mechanical design of battery pack:
Cell:
cell is used to store chemical energy at the time of charging and at the time of discharging it delivers electrical energy. Cell consist of anode, cathode and lithium iron phosphate ( LiFePO4 ) material.
Nominal voltage of cell is 3.3V at 1 C rate and this voltgae decrease if the c rate increases, which can be observed from above data sheet.
length of cell is 66 mm
diameter of cell is 26 mm
Module:
To increase cell ratings, same types of cells are connected in series and parallel.
Extra 2mm length is taken for cell strips and distance between cells assume to be 4mm.
Assuming 25 cells are connected in series in module.
Therfore rating of cell is
Voltage = 25 * 3.3 = 82.5V
Ampere hour remains constant as cells are connected in series.
Therfore One module consists of 25 cells.
Total modules = 2200/25 = 88
if we connect four modules in series, It deliver 330V and 2.35Ah and here it form one parallel path.
Each parallel path consist of four modules and these should be repeated for remaning 22 parallel paths
If connect 88 modules as shown in above figure then it will become battery pack.
This is one of the module configuration. Other module configurations are also possible.
Connections of cells:
Cell are connected with the help of Nickel strips as shown in below figure.
Nickel strips are used because of their heat capablities.
Foil Based components:
It is one large component, and it can easily handled.
Parts Replacement is very easy.
It has cell voltage sensor and Temperature sensore.
It has fuse, if a module is utlizied beyond its limits, then fuse will blow off protecting Module.
Welding:
To connect cells the nickel strips are used. Welding has to be done to connect cell to nickel strip.
Types of welding are
1. Spot Weld
2. Laser weld
3. wire bond
Protection Venting:
These are Plastic or metal shells helps to protect from dust , debris and maintain pressure difference between battery and atmosphere.
Calculating Volume and Weight of a Module.
considering Protection Venting, Nickle strip and Foil based component and battery the Length is 70mm.
This module contains 5 cell in a row and 5 cells in column ( 5 * 5 )
Breadth of Module = ( 26 + 4 ) * 5 = 150mm = 15cms
Volume of Module = Length * Breadth * Height = 70 * 150 * 150 = 1575000mm^3
Volume of Battery Pack=1575000*number of Modules =1575000*88 =138600000mm^3
Weight of Battery Pack = Weight of single cell number of cells=76grams*2200=167200grams = 167.2Kgs
Above figure shows total battery pack