Aim:- To design a battery pack

Objectives:-

            1)design a battery pack with 18kWh capacity

            2)to know about high performance litium iron phospate battery

Theory

• A cell is a component that produces potential diffrence and current duee to the moment of ion between anode and cathode. it works on redox reaction .it consists of positively charged olivines or metal oxide  known as cathode and negatively charged carban based materials like graphite  is known as anode. The space between the anode and cathode is filled with electrolytic material like ethylene carbonate ,dimethyl carbonate,propylene carbonate which contains desolved lithium salts.  

• Use of lithium ion battery is  increased due to its below characterstics

1. High Specific power-ampere hour rateing
2. Long life-depending upon charge discharge and temperature conditions life can be expected to as high as 10 years
3. Safe to operate
4. Intoxic and causes no emmisions dureing  operations

• Battery terminology

            Depending upon form factor litium ion cells are classified as

1. Cylindrical cell-                     

  2.Priesmatic cell

  3. pouch cell

• BATTERY CONECTIONS 

1. Series connection

 when we are connecting a battery with end to end connection i.e positive terminal of one battery is connected to negative terminal of other battery and neagtive terminal on one battery to positive terminal of other battery the connection form is a series connection

 in series connection  the resultant voltage of battery pack is the sum of voltages of individual battery and current is constant i.e no change in current.

eg nominal voltage of battery pack =no. of cells in series *nominal voltage of cell

   2. PARALLEL CONNECTIONS

when positive terminal is conected to positive terminal of other cell  and negative terminal of other cell is connected to negatve terminal of cell then this type of connection is called as parrellel connection. i  this connection current adds up while voltage remains constant

i.e Rated capacity of battery pack=no of cells in parallel*rated capacity of cell

• Nanophospate High power Lithiumion Cell ANR26650M1-B

 A lithium iron phospate battery delevers high power and energy density combined with excellent safety, performance and extensive life cyclweing in a lighter weight and more compact packages .

• Performance characterstic of ANR26650M1-B

 As per manufacturers data sheet  cell has following specifications

• Mechanical designing of a battery pack 

Vehichle sector demands safety and reliablity of a vehicle . Lithium ion batterys are  more affected by traction ,Vibrations caused due to vehicle moment and thermal run away. these incapabilities can be reduced by  designining a robust battery pack which allows cooling and isolating the vibrations

Based on the manufacturers data sheet  we can calculate  energy content,volume,gravimetric density and volumetric density.

• Volume of cell

where Dbc=26mm=0.026m

Lbc=65mm=0.065m

substituting values in above equation

The volume of cell is 0.0345m^3

• Energy of battery cell(Ebc)

where Cbc=2.5

Ubc=3.3V

substituting values in above equation 

Ebc=2.5*3.3

Ebc=8.25W

The energy of unit battery cell is 8.25W

• Volumetric energy density(Wh/m^2)

Ebc=8.25

Vcc=0.0345

substituting these values in above equation

uV=8.25/0.0345=239.13Wh/m^2

The volumetric energy density is 239.13Wh/m^2

• Gravemetric energy density

uG=8.25/0.076=108.55Wh/kg

The gavavemetric energy density is 108.55Wh/kg

• The total battery pack energy is given as 18000W
• Number of cells connected in series in a string-It is evaluated by divideing nominal battery pack voltage to the voltage of each cell. here  as the no of cells are integers we ave to round it up to form integer

Let us assume that nominal battery pack voltage is 360 v 

Ubc=3.3v

substituting these values in above equation

Ncs=360/3.3=110 cells

The number of cells connected in series are 110 

• Energy content in a string(Wh) 

It is the product of number of cells connected in series and energy of battery cell.

Ebs=110*8.25=907.5Wh

The energy content in a string is 907.5Wh

• Number of strings in a battery pack are calculated by dividing total battery energy to energy content of a string

Nsb=18000/907.5=20 strings

i.e no of strings connected in parallel is 20

The number of cells connected in parallel are 20

We can again calculate the battery pack total energy( Eb) as a product  between number of string and energy content of each cell (Es) in Wh

Eb=20*907.5=18150Wh

• Battery pack capacity Cbp [Ah]  is calculated as product between number of strings and the capacity of battery cell Cbc[Ah] 
•                                

              =20*2.5=50Ah

The battery pack capacity is 50Ah

• Total no of cells in a battery pack  B are calculated as a product between the number of strings and number of cells in a string

                                      Nb=Ns*Np

            =110*20=2200 cells

The total number of cells required to design a battery pack of 18 Kw are 2200

the size and mass of the high voltage battery are very important parameters to be considered while designing a battery electric vehicle.In this example we are going to consider only battery cells .in reality other factors are also considered such as electronic circuits,cooling circuit,battery caseing ,wireing.

• The battery pack weight is calculated by product between no of cells in a battery pack and unit cell weight

                                        Mb=Nb*mc

=2200*0.076=167.2kg

The weight of battery pack is 167.2 kg

• The volume of battery pack is calculated by product of number of cells in a battery and volume of single cell

Vb=2200*0.0345=75.9m^3

The volume of battery pack is 75.9m^3

Battery dimensions

1.  Length of caseing

=number of cells*(cell diameter+margin at both the side of a cell)+cleareance

=110*(26+4)+60

L=3360mm

     2.  Breadth of the caseing

breadth=number of cells *(cell diameter+margin at both side of cell)+cleareance

B=20*(26+4)+60

 B=660mm

       3.  Height of the caseing

height =height of cell+marging for wireing

H=65+35

H=100mm

 RESULTS

The number of cells connected in series are 110 

The number of cells connected in parallel are 20

The total number of cells required to design a battery pack of 18 Kw are 2200

The weight of battery pack is 167.2 kg

The volume of battery pack is 75.9m^3

Enclosure dimensions

Length=3360mm

 Bredth=660mm

Height=100mm

Assembly of battery pack

• Components of battery pack

1)2200 cells 

2) Nickel strip for cell conections

3)PVC heat sink film

4)spot welder

5)connectors

6)cell holder

7)solder wire

Step 1

take a cell golder block and snap it according number of  to parallel and series connected cells. the figure below shows cell holder

Step 2

place the cells in a holder matrix

Step 3-

now we are going to connect the cells with nickel strips useing spot welding process. the series connection is made by connecting the positive terminals to negative terminal of other cell while parallel connection is made by  connecting positive terminals together and negative terminals together.

Step 4

Connecting the complete matrix of the cell together

Step-5

connecting the heat sink to the battery pack

now all internal connections are connected as per connections ,battery pack is assembeled

Step 5-

Connect the balanceing wire pin to the BMS

Step 6-

Enclose all the components such as Battery pack , BMS module inside enclosure.

REFRENCES

1)EV design – battery calculation – x-engineer.org

 Conclusion

In this way we had designed a battery pack