Project 1 Mechanical design of battery pack
The performance of the cell is given in the datasheet that is referred to for this project.
These images show the power discharge, current discharge, and the life cycle of the cells used for the battery pack.
Below given data is from ANR26650M1-B cell data.
Energy (Battery pack capacity) = 18 kWh
Cell = ANR26650M1-B
the cell datasheet is given below as attachment.
Voltage = 3.3 V
Capacity = 2.6 Ah
Battery pack Voltage = 231volts (Assumed value).
number of cells in series = Battery pack voltage / Individual cell voltage = 231 / 3.3 = 70
Capacity = Energy / Battery pack voltage = 18000 / 231 = 78Ah.
number of cells in parellel = Total capacity / Individual cell capacity = 78 / 2.6 = 30
now the Battery Pack Configuration is 70S30P.
Total number of cells in the Battery Pack = 70x30 = 2100 cells.
now these 70S30P will be divided into 100 modules each.
Each Module consists of 7S3P configuration with Capacity of 7.8Ah and Voltage of 23.1volts.
it's arrangement as shown below. for my understanding purpose configuration drawn in paper with hand and it's snip attached here.
like that each module will be arranged side by side as shown below. Module 1 positive and negitive terminals are attached to the Module 2 positive and negitive terminals respectively.
Cell Calculations:
Cell Dimensions -
Diameter = 26mm
Radius (r) = 13mm
Height (h) = 65mm
mass = 76g
Volume of a cylinderrical cell = pi*r^2*h = 34492 mm^3.
Density of a cylinderrical cell = 76/34492 = 0.0022 g/mm^3.
Energy of a cell = Cell capacity*voltage =2.6*3.3 = 8.58 Wh.
specific energy density of a cell = 8.58 / 34492 = 2.48x10^-4 Wh/mm^3.
Module Calculations:
In a battery pack, cells will be arranged with some distance in a module and this module will be grouped together to form a battery pack.
let's see the module calculations.
Each Module consists of 7S3P configuration with Capacity of 7.8Ah and Voltage of 23.1volts.
assuming that cell to cell distance in series and parellel(Dcc) = 4mm.
for a module, Length = 78mm
Width = 210mm
module with dimensions are shown below.
volume of the module = 78*210*65 = 10,64,700 mm^3.
capacity of the module = 7.8Ah*23.1v = 180 watts-hour.
weight of the module = 76*21 = 1596grams = 1.5 kg
Density of the module = 1596/10,64,700 = 0.0014 g/mm^3.
Specific Energy of a module = 180wh/ 1.596kg= 112.78 Wh/kg.
10,64,700 mm^3 = 1.064 litre
energy density of a module = 180 / 1.064 = 169 Wh/l.
cell to cell connections are made as shown in above figure. for connecting the cell Nickel strips will be used on top of the cells on both positive and negitive terminals. if we see the the figure these strips are connected in bottom and top.
Indirect cooling system is good for these type of packs because there will be no contact with cells and no damage for BMS. cooling system is needed for packs and module and each cell to control their temperature and it will do by thermal management system in BMS. Indirect cooling system figure is shown below and it is located in bottom of each module to make sure each cell is under thermal control.
Battery Pack Calculations:
if we connect such modules of 100 we get our capacity of 18kwh.
battery pack to get the 18kwh capacity we need below dimensions.
capacity of the battery pack for 100 modules = 180*100 = 18000 watts-hour.
weight of the battery pack for 100 modules = 1596*100 = 159600 = 159.6kg.
by assuming module to module length = 4mm
so, for 100 modules = 4*100 =400mm
Battery pack length for 100 modules is calculated approximately.
for a module Length = 78mm
Battery pack length for 100 modules = 78*100+ 400 = 8200mm
Battery pack Width for 100 modules = 210*100+ 400 = 21400mm
module with dimensions are shown below.
volume of the battery pack = 8200*21400*65 = 11,40,62,00,000mm^3
Area covered by battery pack = 17,54,80,000mm^3.
Density of the batttey pack = 159600/11,40,62,00,000 = 1.399*10^-5 g/mm^3.
Specific Energy of a module or battery pack = 18000wh/ 159.6kg= 112.78 Wh/kg.
energy density of a battery pack = 18000 / 11,406.2 = 1.57 Wh/l.