Project 1 Mechanical design of battery pack
The cell used is ANR26650M1-B for making battery pack with capacity 18 kwh.
The cell specifications are given below-
Therefore,the cell parameters are given below-
Nominal voltage-3.3 V
Rated capacity-2.5 Ah
cell dimensions- 26mm(diameter) x 65mm (height)
weight of cell - 76g
The objective is to get a battery pack capacity of 18 Kwh
Therefore,we have to find out the number of cells needed
This can be done by back calculating-
Energy=voltage x current
voltage = no of parallel cells x cell capacity
current = no of series cells x nominal voltage
therefore,energy = total no of cells x nominal voltage x cell capacity
18000 = 2.5 x 3.3 x total no of cells
total no of cells = 2182.
On back calculating it is found that the number of cells is close to 2200 cells
therefore we assume that there are 2200 cells and they can be made into different combinations of parallel and series ,they are divided into 50 cells series and 44 cells parallel ,so that it can be compact.(50S44P)
then while finding the total energy,
total energy = total no of cells x cell capacity x nominal voltage
= 2200 x 3.3 x 2.5 = 18150 kwh
hence,we can assume this as the number of cells required for the energy requirement
This is the dimension of the cell
From this,we can find the volume of the cell
volume of one cell = 3.14 x radius^2 X height = 3.14 x 13 x 13 x 65 = 34492.8 mm^3 =0.0000344929 m^3
Therefore,Total volume for battery pack = 2200 x 0.0000344939 = 0.07588438 m^3
Total weight of battery pack can also be found out-
Cell weight = 76 g
Number of cells = 2200
Battery Pack weight (W) = cell weight * number of cells + weight of accessories(5 kg)
W = 76 * 2200 + 5
W = 172.2 kg
Cells are made into combinations and are connected using the nickel strip.
Then these combinations are made into a battery module by placing in a cell holder.
The battery module along with the cooling tubes ,pcm are placed into the battery pack enclosure.
Nickel Strip
It is generally useful in the welding of battery points together to connect the batteries in combinations.These Nickel strips are popular because of their good performance while soldering as it gets soldered very quickly;easily with normal soldering metal with High tensile tension and Low resistivity.They have a thickness of 0.1 mm.
Battery Cell holders
Battery Cell Spacer/Holder is a cylindrical battery spacer, made of flame retardant ABS+PC materials, with high-temperature resistance and crack resistance. There are slots on the edge of the holder, that can be combined into many different sizes and shapes of the battery pack;after welding nickel tabs, the pack can pass the vibration test without any other connecting device.It can hold different no of cells depending on the cells of the battery pack.The bore diameter is 26.3 mm for keeping the cell.
the Dimension are 40 x 20 x 8 mm (LxWxH).
By using the battery holders and nickel strip ,the cells are made into a battery module.
now the battery module has to be kept in an enclosure.
This is the typical image of battery pack enclosure containing all the components.
To design the battery pack for our 18 kwh battery pack-
Assume that cooling tube and a PCB is kept together with the battery in the enclosure.
Assume the thickness of the cooling tubes to be 5 mm,two sets of kept on the lower and upper portion of the enclosure to provide sufficient thermal management.The thickness of the pcb can be taken to be 3mm.
Dimensions of battery pack casing are calculated-
Length of casing (L) = number of cells at series * (cell diameter (26) + margin at both side of cell (4) + clearance at side (diameter of edged cell + margin)
L =50*30 + 60
L =1560 mm.
Breadth of casing (B) = number of cells at parallel * (cell diameter (26) + margin at both side of cell (4) + clearance at side (diameter of edged cell) + margin)
B = 44*30 +60
B =1380 mm.
Height of casing (H) = 65 +35 (height of cell + margin, cell holder and nickel strips) +thickness of cooling tubes + thickness of pcb
H = 100 +30+10+3=143mm.
Final design of the battery pack enclosure
This is the top view of the battery pack enclosure
This is the side view of the battery pack enclosure
50S44P configuration of cells are placed in this enclosure.
Therefore ,design of battery pack with enclosure is done.