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.
Cell: ANR 26650 M1-B is Lithium Ion Phosphate Chemistry.
Voltage: 3.3 V
Capacity: 2.56Ah
Required Battery pack Capacity: 18 KWh = 18000Wh
Considering the Electrical and Mechanical Characteristics of the cell as shown below:
Electrical Characteristics:
Voltage = 3.3 V :
Capacity = 2.56+/-0.1 Ah ;
Energy = 8.25Wh;
Specific Power > 4000W/Kg;
Cycle lifetime 100% DOD >4000 cycles
Max continuous discharge current = 50A (20C rate)
Max Pulse Discharge Current 120A (48C rate);
Max Pulse Charge Current 20A (8C rate); Float voltage 3.45V;
Mechanical Characteristics:
Diameter = 25.96 +/- 0.5 mm;
Length = 65.15 +/- 0.5 mm;
Mass = 76g +/- 1.0g
Different combinations (Series and Parallel) of the cells are considered to get the 18Kwh capacity for the battery pack.
Values of Voltage, Capacity, Mass are considered as per the data sheet given below.
Different combinations of Series and Parallel sets are given below
Formulae use to fill the below table are:
Considered the number for Series and Parallel connection.
Example: No.of series cells 72;
No. of Parallel Cells: 30
Total battery pack voltage: No. of Series cells * Cell Voltage = 237.6
Total battery pack Charge = No. of Parallel cells * Cell charge = 76.8Ah
Total Capacity = V*Ah = 18.247Kwh
Total No. of cells = 30 *72 = 2160
As Mass of the cell considered as 76g;
Total weight of the battery = 76g *2160=164.160 Kg
Other combinations of series and Parallel sets of cells are considered to achieve the specific voltage and current ratings.
Total weight of the unit is also calculated for different combinations of Series and Parallel sets.
|
Series |
72 |
70 |
73 |
75 |
71 |
61 |
53 |
89 |
|
Parallel |
30 |
31 |
30 |
29 |
30 |
35 |
40 |
24 |
|
Total No.of batteries |
2160 |
2170 |
2190 |
2175 |
2130 |
2135 |
2120 |
2136 |
|
voltage |
238 |
231 |
241 |
248 |
234 |
201 |
175 |
294 |
|
Current |
76.8 |
79.36 |
76.8 |
74.24 |
76.8 |
89.6 |
102.4 |
61.44 |
|
Capacity |
18.25 |
18.33 |
18.5 |
18.37 |
17.99 |
18.03 |
17.9 |
18.04 |
|
Weight of the pack (Kg) |
164.160 |
164.920 |
166.440 |
165.300 |
161.880 |
162.260 |
161.12061 |
162.336 |
As per the above comparison table, the series and Parallel sets are chosen to the nearby value of the battery.
The assumed set of cells are 61 in Series ad 35 sets of series cells in parallel.
The total number of cells is 2135
Battery pack voltage is 201V, 89.6 A of current storage with 180.03 KWh capacity.
Weight of the battery pack with cells is 162.260Kg.
Now the space occupied by the cell is:
Length 65.15mm
Diameter: 25.96 mm
Volume of each cell = 3.14 *65 *26^2 = 0.03451 m^3
Energy of each cell = Cell Capacity * cell Voltage = 2.6 *3.3 = 8.58 Wh
Volumetric energy = Single cell energy/ Volume of each cell
= 8.58wh/0.03451 m^3
= 248.62 Wh/m^3
Gravimetric Energy (Wh/Kg) = Single Cell energy/Mass of each cell
= 8.58/0.076
=112.89 Wh/kg
Cell peak current (A) = Max charge Current (C rate) * Single Cell capacity
= 10 * 2.5
=25 A
Battery Pack peak current (A) = Cell peak current * No. of cells connected in parallel
=25*35
= 875 A
Battery pack Peak power (W) = Battery pack peak current *Voltage if cells connected in series
= 875 *201
= 175.875KW
Battery Pack Assembly:
- Selecting the No. of Cells and arrangement in series-parallel sets are calculated.
- Choosing the battery strips
- Welding the strips using either spot welding or soldering.
- Checking the cell voltage
- After checking each cell voltage, the battery pack is arranged and the final voltage and capacity of the pack are checked.
- Assemble the cells in the series and parallel combinations as per the requirement.
With the help of spot welding, Nickel strips are welded and the entire battery pack is available as per the requirement.
Now the Battery management system is to be added which is the electronic system that manages the lithium battery pack.
Finally adding the battery pack in the Printed Enclosure
Final assembly of the battery pack
Reference Data sheet:
References:
https://www.instructables.com/DIY-Professional-18650-Battery-Pack/