Project 1 Mechanical design of battery pack
OBJECTIVE 1 : Battery pack capacity: 18 kWh
Cell: ANR26650M1-B
Prepare a detailed battery pack drawing along with its enclosure. State your assumptions.
SOLUTION : To design a battery pack of 18kwh a cells of ANR26650M1-B and discuss steps involved in designing a battery pack.
A123's high performance Nanophosphate lithium ion phosphate (LiFePO4) battery technology delivers high power. The energy desity combined with excellent safety performance and extensive life cyclling in a lighter weight, more compact package cells have low capacity loss and impedance growth over time as well & high usable energy over a wide state of charge (SOC).
These allows the systems to meet end-of-ilfe power and energy reqirements with minimal sizing.
Specification of cells are :-
Electrical Configuration :-
Single Cell Voltage = 3.3V
Rating = 2.56Ah
Capacity of single cell = 3.3*2.56 = 8.448 Wh
Now assuming battery pack voltage of 330V
Series & Parallel Connection :-
Cell voltage = 3.3 V
Battery Pack Voltage = 330V
Ns(Series) = 330/3.3 = 100 cells
As per question required capacity = 18000wh
Voltage = 330V
Current = 18000/330 = 54.54 Ah (High voltage and low current combination is prefereed to avoid thermal losses)
Rating = 2.56Ah
So 54.54/2.56 = 21.3
So Np (Parallel) = 22 cells
So total no cells in battery is given by 100*22 = 2200 cells
MECHANICAL DESIGN OF BATTERY PACK :-
Cell : It is used to store the energy in the form of chemical energy and converts it into electrical energy while charging and discharging
Nominal voltage of cell is 3V at 1C rate
MODULE :-
To improve the cell rating cells are connected in combination of seriesand parallel as shown below
Let 25 cells be in series
Voltage = 25*3.3 = 82.5 V
AH is constant in series
Therefore one module have 25 cells
Total module =2200/25 = 88
So 4 modules each with 25 cells will be in series with 22 such parallel connections.
VARIOUS TYPES OF CONNECTION OF CELLS
FOIL BASED COMBINATION
It is one large component and it can easily be handled with easy replacements
It has both voltage and temperature sensor with fuse for protection.
WELDING
To connect cells the nickle strips are used. Welding has to be done to connect cell to nickel strip.
Types of welding are
1. Spot Welding
2. Laser Welding
3. Wire Welding
CALCULATION OF VOLUME AND WEIGHT
Considering Nickle strip and foil based component and battery with length = 70mm
Let the battery is of 5*5
Width = 26+4 = 150mm = 15cm
Volume of module= L * b * h = 70*150*150 = 1575000mm^3
Volume of battery pack = 1575000*88 = 1686*10^4
Weight of battery pack = Single cell*No of cells= 76*2200 = 167200gm = 167.2kg
