Project 1 Mechanical design of battery pack
Mechanical design of battery pack
To prepare a detailed battery pack drawing along with its enclosure with ANR26650M1-B by a capacity of 18kWh.
ANR26650M1-B is a nano phosphate high power lithium ion cell which is made by lithium iron phosphate (LiFePo4). This is more powerfull and have high energy than other cells and lower impedance it has high efficiency with more safety precautions also having long life. It has wide range of SOC with less losses which leads to less discharge for long range with lighter weight. These cells have low capacity loss and impedance growth over time. The application of the these type battery are used for high power and energy as transmission and distribution, grids, power plants, Ev and HEV vehicles, military machines and vehicles.
From the datasheet of the ANR26650M1-B,
ANR26650M1-B Battery
ANR26650M1-B Technical data
From the above 3 different graphs it shows the,
1.Constant power discharge characteristics at 23℃ : From observing the graph changing the power that is by increasing the power at constant temperature it decreases the voltage respectively.
2.Constant current discharge at various temperatures : From the graph changing the temperature from 45 degrees to -15 degrees it reduce respectively as shown above.
3.Cycle life performance,100% DOD, various temperature and discharge rates : In this as we can see that by changing the charging and discharging cases as shown its peformnace characteristics changed here (+) represents charging and (-) represents discharging. By changing the temperatures its performance change.
Design of the ANR26650M1-B cell,
As we know that the safety, designing, sizing and some other things are more important to any of the object they play the key role for the transport, manufacturing etc. if we see these aspects in the lithium-ion cell batteries it is difficult to transport the battery because of the vibrations, exposure of high impact of the forces and thermal run away. To avoid all these to small the robust mechanical designs are necessary. here the mechanical designs play a major role before using in the vehicles. So the designing of battery packing provide a greater degree of protection against so many of these.
The major parts of the battery cell are five they are, anode, cathode, separators, elctrolyte and terminals. A battery consist of one or more elctro chemical cells which are converting chemical energy into electrical energy at the time of discharging and electrical energy to chemical energy at the time of charging.The chemical reaction occurs at the time of charging and discharging is called chemistry of the battery. And the types of cells used are cylindrical, flat, pouch etc.
A battery has a set of modules which is be in certain design with set of cells connected. The modules and batteries are connected or configured in a series, parallel or in both based on the requirement by this the outlook of the battery pack is decided. By changing the same cells with different design, it changes the voltage and capacity values but the power remains same in the circuit. The battery pack consist both hardwares and software components which is cell and BMS respectively.
The perfomance chracteristics:
In this graph, The points between the line is 25% each. In the specific energy line, it shows 2 points which is 50% of energy. In the specific power shows 4 full points means 100% of power as an output from the battery. In the safety point of view, is also shows 4 full points that is 100%. From the performance side it shows only 75%. The life span of the battery is 100%. In view of cost its less compared to other.
Assembly line of a cylindrical battery:
The main parts of a battery system are cells, modules, BMS, wires, strips, case, separators, insulators, sensors etc. 
These are process to make cylindrical battery cell and to make battery pack it is made by,
This how a battery pack is made in this process we use different machines such as Auto sticker machine, auto sorting machine, spot welding machine, shrinking machine, code printing machine, and aging machine.
Battery calculations
Values from the datasheet
- Number of cells(n) = Energy / (Nominal voltage*capacity)
N = 18000/(3.3*2.5)
N = 2182 cells
To get 18kWh energy we need minimum of 2182 cells and need to decide the configuration as series or parallel.
In series configuration capacity remains the same and voltage will be the sum of individual cell voltage.
In parallel configuration voltage will be the same and capacity accumulates.
And here we assume 300 volts needs to run the vehicle.
The capacity of the total battery for 18kWh is
Capacity = 18000/300
Battery capacity = 60Ah
The nominal voltage of 1 cell is 3.3V
Number of series cells required to produce 300V (Ns) = voltage required/nominal voltage of one cell
Ns = 300/3.3
Ns = 90.9
Ns = 91 cells in series
So, to produce 300V of voltage we required 91 cells of ANR26550M1-B in series which having 3.3V, the excess voltage be considered in losses.
The capacity of the whole module will be 2.5
The number of cells which will be connected in a parallel configuration
Np = 60/2.5
Np = 24
Np = 24 cells in parallel
Here we use 24 cells are in parallel to run the battery with 60Ah capacity.
The total cell model is having the pack of 91S24P configuration.
Battery module:
The total battery power = (91*3.3V) * (24*2.5Ah)
= 18018Wh
= 18.018kWh
The battery requirement is 18.018kWh, The required configuration is 91 series cells and 24 parallel cells.
To build such a large grid , we need to slip the battery packs into the battery module, which reduce the complexity of monitoring and optimising battery management and minimizing battery damage. For that we use the modules which take care of cells protection, monitoring, connections of set of the cells.
here we divide the cells from 91S24P into 7S4P.
so the no of cells in each module are = 7*4
= 28cells
Total no of cells = 2184 cells
no of modules = 2184/28 = 78 modules
We have already calculated battery capacity which is 60Ah means it is going to supply 60A current per hour. Which can be considered as C-rate of the battery.
Let us assume the energy consumption for 1km is 100Wh. So, the total range of the battery for 18kWh is 180Km
So the vehicle will run 180km in a full charge.
Battery enclosure pack size:
ANR26650 cell has 26mm diameter and 65mm height. on the basis of that we need to decide battery size of battery casing which is total battery pack.
Length of casing (L) = number of cells at series * (cell diameter (26) + margin at both side of the cell which to free up space called holders and gaps for the sheet protectors etc (4) + clearance at side (diameter of edged cell + margin) (all should be in value with mm)
L=91*30+80
L=2810mm
Breadth of casing (B) = number of cells at parallel * (cell diameter (26) + margin at both side of the cell (4) + clearance at side (diameter of edged cell + margin)
B=24*30 +80
B=800mm
Total area of the battery is = 2810 * 800
= 224800mm
=2.248
Height of the battery (H) = 65 (height of the cell) + 35 (wires, holders, strips etc)
= 100mm
Volume of the battery = L*B*H
= 2810*800*100
= 0.224m
Here we find all the values for our battery.