Project 1 Mechanical design of battery pack
Mechanical design of battery pack
Battery pack capacity:18 kWh
Cell:ANR26650M1-B
The high voltage battery is one of the most important component of a battery electric vehicle(BEV).the battery parameters have a significant influence on other components and attributes of the vehicle,like
- maximum traction motor torque
- maximum regeneration brake torque
- vehicle range
- vehicle total weight
- vehicle price
A battery cell consists of five major components:electrodes-anode and cathode,seperator,terminals,electrolyte and a case or enclosure.
Individual battery cells are grouped together into a single mechanical and electrical unit called a battery module.The modules are electrically connected to form a battery pack.
battery pack consists of number of series and parallel combination.large battery pack consists of large number of modules.
Series connection is used to obtain required voltage and parallel connection is used to obtain required current capacity.
In order to ensure safe and reliable operation of battery pack design should follow certain technical criterias
- Mechanical vibration should be less
- controlling on high impact force
- Better thermal runaway for cooling
- Serviceability and recyclability
Technical specifications of ANR26650M1-B
Calculations as per the assumptions : 18kWh battery pack capacity
18kWh is the energy required to achieve vehicle its proper range.it depends on the voltage parameter and ampere hour or capacity(Ah).
The design is for high voltage battery pack of electric vehicle in order to achieve range upto 250km.
Assumed value for nominal voltage for series connection is 145.2V
Diameter=26mm=0.026m
Length=15/65mm=0.065mm
Mass=76g=0.076kg
single cell voltage = 3.3V
capacity=6Ah
Max continous charge current(C-rate)=10A
Max pulse charge current(C-rate)=20A
Mathematical battery calculation
single cell calculation ,volume of cell=πr^2h
πr^2h=3.14*0.013^2*0.065
=0.03451m^3
single cell energy(Wh)=Cell capacity (Ah)*Cell voltage(V)
=2.5*3.3
=8.25Wh
volumetric energy (Wh/m^3)=single cell energy/volume of each cell
=8.25/0.03451
=235714Wh/m^3
Gravimetric energy(Wh/kg)=single cell energy/single cell mass
=8.25/0.076
=108.55Wh/kg
Total number of the battery pack
Ebp=18000Wh
Number of cells connected in series
It is calculated by dividing the nominal battery pack voltage of each battery cell.The number of strings must be an integer.
Ns=(Ubp/Ubc)
By assuming the battery pack voltage to be 330V and the nominal voltage of the battert as per the datasheet as 3.3V
Nbc=Ubp/Ubc=100
Total number of cells in series is 100
Energy content of a string
The product between the number of battery cells connected in series and the energy of a battery cell
Ncs=Ubp/Ubc
Ebs=Ncs.Ebc=100*8.25=825Wh
Number of strings in the battery pack
It is calculated by dividing the battery pack's total energy Ebp(Wh) by the energy of the string Ebs(Wh)
Nsb=Ebp/Ebs=18000/825=21.81
All the 2 strings are connected in parallel
Battery pack capacity
it is calculated as the product between the number of strings Nsb and the capacity of the battery cell Cbc(Ah)
Cbp=Nsb.Cbc
=22*2.5
=55Ah
Total number of cells of the battery pack
It is calculated as the product between the string Nsb and the number of cells in a string Ncs
Ncb=Nsb*Ncs
=22*100
=2200
Total number of cells required for the design pack is 2200
Mass of the battery pack
It is the product of total number of cells Ncb and the mass of each battery cell Mbc
Mbp=Ncb*Mbc
=2200*0.076
=167.2kg
Volume of the battery pack
It is product of the total number of cells Ncb and the mass of each battery cell Vcc(pc)(m3)
It is used to estimate the final volume of the battery pack since it does not take into account the auxillary components of the battery
Vbp=Ncb*Vcc(pc)
=2200*3.5*10^-5
=77000mm^3
String peak current
It is the product between the peak C-rate of the battery cell C-rate bcp(h^-1) and the battery cell capacity Cbc(Ah)
lspc=C-ratebcp*Cbc=24*2.5=60A
Battery pack peak current
It is the product between the string peak current lspc(A)and the number of strings of the battery pack Nsb
lbpp=lspc*Nsb
=60*22=1320A
Battery pack peak power
It is the product between battery peak current lbpp and the battery pack voltage Ubp
pbpp=lbpp*Ubp=1320*330=435.6kW
String continous current
It is the product between the continous C-rate of the battery cell C-ratebcc(h^-1)and the battery cell capacity Cbc(Ah)
lscc=C-rate bcc.Cbc=10*2.5=25A
Battery pack continous current
It is the product between the string continous current lscc(A) and the number of strings of the battery apck Nsb
lbpc=lscc.Nsb
=25*22=550A
Battery pack continous power
It is the product between battery pack continous current lbpc(A) and the battery pack voltage Ubp(V)
Pbpc=lbpc*Ubp=550*330=181500w
The battery pack continous power will be 181.5kW
Assembly of the battery pack
Step 1:Snap the square cell holder together
Step 2:Place the cells in the holder matrix.Place all the cells in the holder and place the second holder in the place.
Step 3:Connect the cells with nickel strips using spot welding process.Series connection will be made by connecting positive terminal of the cell to the negative terminal of another cell.parallel connection is made by connecting the same terminals.
Step 4:Connect the heat sink to the battery pack
Step 5:Connect the balancing wire pin to the battery management system.
Step 6:Place the enclosure for the battery pack
Cell holder
cell cover
Final battery model
CONCLUSION
From the single cell data,battey pack has been designed for electric vehicle application which is having total energy of 18kWh
The steps involved in the design and developement of the battery has been mentioned.