Project 1 Mechanical design of battery pack
AIM:-
Prepare a detailed battery pack of Cell: ANR26650M1-B, drawing along with its enclosure, & Battery pack capacity is 18kWh. State your assumptions.
Abstract:-
- In this project, we are going to calculate the all parameters which are required for the build EV battery pack.
- We are going to use the Cell: ANR26650M1-B for our battery pack. In parameters, we will consider all electrical aspects like temperature, Depth of discharge, Operation current, Energy density, Work cycles, Battery capacity, State of Charge (SOC), State of Health (SOH), Ampere-hour (Ah) Capacity.
- We also calculate all geometrical considerations like size, weight, volume, area, etc. In the end, we consider some enclosures model for our battery pack.
Theory:-
Battery pack architecture:
All high voltage battery packs are made up from battery cells arranged in strings and modules., A battery cell can be regarded as the smallest division of the voltage.
Individual battery cells may be grouped in parallel or series as modules. Further, battery modules can be connected in parallel and/or series to create a battery pack. Depending on the battery parameters, there may be several levels of modularity.
The total battery pack vtg is determined by the number of cells in series. For example, the total (string)voltage of 6 cells connected in series will be the sum of their individual voltage.
In order to increase the current capability the battery capacity, more strings have to be connected in parallel. For example, 3 strings connected in parallel will tripple the capacity and current capability of the battery-pack.
An example is the high voltage battery pack of Tesla Model S, which has:-
- 74 cells in a parallel-group
- 6 groups in series for a module
- 16 modules in series
- 7104 cells in total
Battery pack production line:
PROCEDURE:-
- first we have to start with Cell calculation.
- Then we will do Battery Pack assumptions.
- After assumptions, we have to do Battery pack calculations.
- From Cell Dimensions we calculate the surface required for a battery pack.
- Depending upon the above calculations we build Battery Pack construction.
Dimension of the cells:
Calculation :
This calculation is to determine how much space of volume the cell will take in the to have the capacity of 18kw.
Cell energy=Nominal volatge X niminal cell capacity
Cell energy=3.3X2.5
=8.25Wh
sor each cell has the energy of 8.25 wh.
Cell Volume=π *r*r*h
=3.14x0.013x0.13x0.065
=0.0344929 m^3
So now we have to calculate how much Watt per volume the cell can produce:
Cell energy density =cell energy/cell volume
=8.25/0.0344929 Wh/m^3
=239.17 wh/m^3
Now we have to assume the battery pack:
To get 18 kw as a output power we have to conside serises and paraller cells to be connected to create the battery pack module of the required capacity.
let us consider 58 cells connected in series a and 38 cells connected in parallel.
- So the toatal number of cells required =58X38=2204 cells
Voltage of the pack =Nominal volatge X cell connecetd in series
=3.3x58
=191.4
current capacity of the battery pack=Cell capacity X Cells conned in parallel
=38x2.5
=95Ah
The total energy of the battery pack =Volatage X current capacity
191.4x95
=18.18KW
Now we know the total number of cells which are required in the battery pack we can now calaculate the energy density,volume and weight of the enitre batery pack.
Total volume =Cell volume X Total no of cells
0.0344929x2204
=76.022m^3
And
total weight of the battery=Total no of cells X Weight of each cell
2204x0.076 kg
=167.504 Kg is the total weight of the battery
Now we know the weight and volume of the battery pack of 18kw .So, we will consturct the battery pack.
Battery Pack:-
- A battery consists of one or more electrochemical cells (battery cells) which are converting chemical energy into electrical energy (during discharging) and electrical energy into chemical energy (during charging).
- The type of elements contained within a battery and the chemical reactions during discharging-charging events define the chemistry of a battery.A battery cell consists of five major components: electrodes – anode and cathode, separators, terminals, electrolyte and a case or enclosure
- Individual battery cells are grouped together into a single mechanical & electrical unit called a battery module.
- The modules are electrically connected to form a battery pack.
- There are several types of batteries(chemistry) used in hybrid & electric vehicle propulsion systems but we are going to consider only Lithium-ion cells. The main reason is that Li-ion batteries have higher specific energy [Wh/kg] & specific power [W/kg] compared with other types.
Ev uses mainly 3 types of cells:Cylindrical,prismatic and pouch.
Battery Pack construction:
There are 3 steps for the construction of the battery pack.
1) Battery holding & providing the spacing between the battries.
2) Connecting the battries with the strips (Series or Parallel).
3) making & manifacturing the battery enclosure housing with the thermal managment system and BMS.
1)Holding and spacing:
- Each of the cells are now needto be connected so that it could form a big battery module.
- So this holdes are very importatnt to provide the gapp between the battery and holding the battries in the correct manner.
- The cells has a vent at the end cap of the cell.& should not be covered by any mechinical means.Blocking the cell vent and then sufficiently abusing the cell so as to built the pressure in cell.There must be minimum of 1mm spacing between each cells to allow the vent to open under the fault condition.
- Holders will make it easy to palcethe contact plate b/w the cells.
2) Connecting the cells:
- When the cells are plalced in the holders; then the cells need to be connect in the proper manner in series or parallel to get the desired results.
- Ususally a nickle strip is used between the cells to make the conatct.
- Nickel strip is generally used in battery building.
- It's due to its efficiency of usage in spot welding and soldering as well its high corrosion resistance over time.
- It has good properties & excellent resistance to many corrosive environments.
- The pure nickel will never get rust after it applied to battery packs.
- It willnot affect the current transfer between batteries.Pure nickel strips are the material you want, but many vendors swap out it for nickel-plated steel strips, which are poorer and have greater resistance – not suitable for most battery projects. 100% pure nickel strip.
- verify all of our strips to assure that you are getting the high-quality pure nickel. It also solder incredibly quickly, so you can weld them on-to your existing busbar connections to raise the supply of current you can pull through the busbars. The benefits are nearly limitless,
3)Battery enclosure and thermal managment of battery and BMS-
- The battery encolsure is the final protection of the batery.
- So the battery enclose must be very strong and light in weight.
- In the case of any accident the batteries has the tendentcy of catch fire if it get leaked during the car crash;so the battery modle is enclose in a very strong encolsure due to the safety.
- The weight should be less so we can get thesuitable best possible range.
- In this metal housing there is temperature managment system provided to cool and heat the battries when there is a need to get the best performace of the battries.
- There a several numbers of models connected in series and parallel- to build a entire battry pack.
BMS:-
A battery management system (BMS) is an electronic system that manages a lithium battery pack and the main functionalities are-
1. Monitors all of the parallel groups in the battery pack & disconnect it from the input power source when fully charged
2. Balance all the cells voltage equally.
3. Doesn't allow the pack from overdischarged.
Conclusion:-
Thus we have studied how to model a battery pack with 18KW battery capacity.