Project 1 Mechanical design of battery pack

Battery pack capacity: 18 kWh

Cell: ANR26650M1-B

Battery contributes one of the most important factor in ev vehicles as pricing of the vehicle depends on what type of electric vehicle are we using and it should be taken care.

Battery contains number of cells and there are hundreds number of cells, the packaing of the cell alos really matters and they should be occupied in such a way that they occupy least volume and also they should not get damaged by heat.As battery should be taken well acre becuse it divides overall capacity and kilometers it's going to ride.Nominal capacity: 2.5Ah at 0.5C rate
Minimum capacity: 2.4Ah at 0.5C rate,Nominal voltage: 3.3V,Charge end voltage: 3.6V
Standard charge current: 2.5A (1C),Fast charge current: 10A (4C)
Max continuous discharge current: 25A (10C),Max pulse discharge current (10 sec): 60A (24C),Discharge cut-off voltage: 2.0V,AC impedance at 1KHz: 6mΩ,Weight: 76g.

depending upon the above conditions for the cell the battery pack is to be decided,before deciding that we should also consider the dimension of the battery-

it has a length of 0.065meter

diameter- 0.026m

mass- 0.076

capacity- 2.5

voltage - 3.3

c-rate(const)- 10

c-rate(peak)-24

volume of the battery peak-

volume of cylinder- (3.14/4)*D^2*h;

= 0.03451m^3.

single cell energy of the battery-

cell capacity *cell voltage(V0=

2.6*3.3

8.58Wh.

volumetric energy(wh/m^3)

8.58/0.03451 = 248.62 wh/m^3.

Gravemtric energy=

8.58/0.076= 112.89wh/kg.

1. The Battery pack total energy E_b[Wh]

To calculate the battery capacity i am using a distance of 220km and Eb(wh-km)=Eb/kilometer= 18000/220=82wh(km)

2. The Battery pack Voltage, Ub[V]

The battery pack capacity is to be considerd to be at voltage of 300v,so number of series cells requiredm for that voltage.

3. The number of battery cells connected in series N_s

Number of cell connected in series dpends upon the battery pack capacity/cell capacity= 300/3.3=91

4. The energy content of a string E_s[Wh]

so the total energy content in the cell is equal to number of cells in series and the energy in each cell- 91*8.25= 750.75wh

E_s = 91 * 8.25 = 750.75 Wh

5. The number of battery cells connected in Parallel, Np

This depends upon net energy of the pack divided by the capacity of the each cell in series =

18000/750.75 = 24.

6. The battery pack capacity C_b[Ah]

This depends upon the capacity of each string and number of strings which are in parallel-

24*2.5 = 60Ah.

7. The total number of cells of the battery pack Nb

This depends upon number of cells in series and number of such strings in parallel-

91*24= 2184 cells

8. The battery pack mass (cells only) m_b [kg]

The net weight of battery pack capacity is total number of cells multiplied by weight of each cell- 2184*0.076 = 165.98kg

9. The volume of the battery pack (cells only) V_b[m³]

The volume of the battery pack is equal to number of cells multiplied to the volume of each cell-

V_b = 2184 * 0.034510 = 75.37 m³

10. The string peak current I_spc[A]-

It's the peak capacity rate of the battery and the battery capacity rate of the battery-

24*2.5=60A

11. The battery pack peak current I_bp[A]

The battery peak current is the peak coulumb rate of the battery and the battery peak capacity of the battery -

60*24 = 1440A

12. The battery pack peak power P_bp[W]

the peak power of the battery is voltage of the battery and the peak ccurrent -

1440*300= 432 kw

BATTERY MODULE

• The battery requirment is 91series and 24parallel and this is creating a huge modle and let's break it down to module which are good enough to do all this let's break it down to 8s and 5p and this will be better than previous one.

So, we are Splitting the 91S24P 2184cells into no of 8S5P Cell Modules

no of cells which are in battery pack is 2184 cells.

No of cells in battery module is 8s5p.

2184/40 = 55 cells in each module.

Cell Configuration in a module = 8s5p

Cell dimensions-

Here each cell weight 0.076kg.

Cell holder-

This also plays a very important rule as cell holder should be stiff enough to not get loose wile vibration and it should make the battery connection easier, and the design is done in such a way that it should give required space to battery to expand, while charging and discharging.

the above is 8 series sand 5 parallel battery cell.

Nickel Strips/Tabs:

• Conductive metal strips are spot welded between all the cells of an electric bicycle battery pack. Nickel is the material of choice due to its low relative resistance and ease of spot welding.
• Pure nickel strip is ideal for use in the building of batteries. As the alloy has high corrosion resistance, can be efficiently spot welded and soldered and offers good conductivity with low electrical sensitivity, it allows battery sources to perform well, even in highly corrosive environments.
• Resistance spot welding, micro TIG welding, and laser welding processes all enable high quality volume production. The selection of one technology over another is usually made based on the application’s specific requirements and the alignment of the technology to these needs.
• We use a nickel tab to connect the cells to make a battery pack. It has 4 markings, which can be spot welded between the battery and the trip using any spot weld technique.
• The thickness of the strip is 0.3 mm, length and width are 38.7 mm and 10.7 mm.
• Connections are made by connecting parallel and in series.

Battery manament system -

This play the most crucial role of the battery and this helps to control over voltage and under voltage and controls the discharge current and the soc of each cell.It has been designed in such a way that it controls the discharge current and the charging limits of each cell so that no battery undergoes overvoltage which may harm his battery life.

No of cells in string [-]	91
String energy [Wh]	750.75
No of strings [-]	24
BP energy [kWh]	180.2
BP capacity [Ah]	60
No total cells [-]	2184
BP mass [kg]*	165.98
BP volume [l]*	75.37
BP peak current [A]	1440
BP peak power [kW]	432

Refrence-

https://x-engineer.org/ev-design-battery-calculation/

https://mpoweruk.com/pack_construction.htm