Project 1 Mechanical design of battery pack

Project 1:

To Prepare a detailed battery pack drawing along with its enclosure

Battery pack capacity: 18 kWh

Cell: ANR26650M1-B 

 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.

OBJECTIVE: 

1) Collecting the data of Cell: ANR26650M1-B from Nanophosphate High Power LithiumIon Cell PDF.

2) Calculating all Electrical parameters for 18 kWh Battery Pack.

3) Calculating all Physical dimensions for Battery Pack.

4) Consider perfect enclosure for dimensions that we calculated for the Battery Pack

Specifications:

ANR26650M1-B Specifications
 Nominal Ratings
  Voltage: 3.3 Volts
  Capacity: 2.5 Ah
  Energy: 8.25 Wh
  Specific Power: 2600 W/kg
  Impedance (1KHz AC Typical) 6 mΩ
  Cycle Life at 1C/1C, 100% DOD: > 4000 cycles
  Cell Type: 26650 Lithium Ion Power Cylindrical Cell

 Discharging
  Max Continuous Discharage: 50 A
  Max Pulse Discharge Current >50% SOC (10s): 120 A
  Minimum Voltage: 2 Volts
  Temperature: -30ºC to 55ºC

 Charging
  Recommended Standard Charge: 2.5 Amps
  Max Charge Rate: 10 Amps
  Max Pulse Charge Current <50% SOC (10s): 25 A
  Float Voltage: 3.45 Volts
  Recommended charge V & Cut-off Current: 3.6 Volts, taper to 125mA
  Temperature
    (reduce charging current to 250mA when under 0ºC): 0ºC to 55ºC

DATAS FROM DATASHEET:

CONSTANT POWER DISCHARGE:(23* C)

2.5C Constant Current Discharge at Various Temperatures:

Our cells have a low capacity loss and impedance growth over time as well as high usable energy over a wide state of charge (SOC) range, allowing our systems to meet end-of-life power and energy requirements with minimal pack oversizing.

A123’s high-performance Nanophosphate lithium iron phosphate (LiFePO4) battery technology delivers high power and energy density combined with excellent safety performance and extensive life cycling in a lighter weight, more compact package. 

PROCEDURE:

1) First we have to start with Cell calculation.

2) After assumptions, we have to do Battery pack calculations.

3) from Cell Dimensions we calculate the surface required for a battery pack.

4) Depending upon the above calculations we build Battery Pack construction

CALCULATION PARTS:

A)CELL DIMENSIONS:

Assumptions: We Assume EV Battery Pack Voltage is 230 V

KNOWN DATA FROM DATASHEET:

• Cell Diameter = 26 mm or Cell Radius = 13 mm
• Cell Height = 65 mm
• Cell Capacity = 2.5 Ah
• Cell Voltage = 3.3 V
• Cell Weight = 76 g

Calculations:

Single Cell Calculations:

1) Volume Of the Cell:

For Cylindrical Cells Voume = pi*r^2*h

Where, Radius = 0.013m

             Height = 0.065m

Volume = 3.14*(0.013)^2*0.65

Volume = 0.0000344929 m^3 or 3.45*10^5 m^3 //

2) Energy Of Single Cell:

E_cell = C_cell * U_cell

_Where,

• E_cell [Wh] – battery cell energy, in watts-hour
• C_cell [Ah] – battery cell (current) capacity, in amperes-hour
• U_cell [V] – battery cell voltage, in volts

Energy, E_cell = 2.5 * 3.3 = 8.25 Wh

Energy, E_cell = 8.25 Wh//

3) Energy Density Of A Cell or Volumetric Energy:

Volumetric energy (Wh/m³) = Single Cell Energy / Volume of each cell

Volumetric energy (Wh/m³) = 8.25 Wh / 0.0000344929 m³

Volumetric energy (Wh/m³) = 239179.65 Wh/m³

4) Specific Energy Density Of A Cell:

Specific Energy Density (Wh/kg) = Single Cell Energy / Weight of each cell

Specific Energy Density (Wh/kg) = 8.25 Wh / 0.076 kg

Specific Energy Density (Wh/kg) = 108.55 Wh/kg //

B) Battery Pack Calculation:

By using Cell Dimension, We can Calculate Battery Pack Calculation by using series and Parallel Connections.

1) Number Of Cells in a Battery Pack:

W.k.t, Energy Of Single Cell =  8.25 Wh//

Required Battery Pack Energy = 18,000 Wh

No.of Cells = 18000/8.25 = Approx 2182//

So, it Clear that minimum No. of Cells Required is 2182//

a) Series Cell Connections,

Assumptions, We Assume EV Battery Pack Voltage is 230 V//

Voltage Depends on the series Connection,

No. of Cells in series = Assumed EV Voltage / Voltage Of a Single Cell

No. of Cells in series = 230 / 3.3 = 69.69

No. of Cells in series =70//

b) Parallel Cell Connections,

Current Capacity Depends on the Parallel Connection,

E_Pack= C_Pack * U_Pack

W.k.t, E_{Pack ,}Required Battery Pack Energy = 18,000 Wh

          U_Pack,Assume EV Battery Pack Voltage = 230 V

C_Pack= E_Pack / U_Pack

C_Pack= 18000/230 = 78.26 Ah//

To Attain this Current Capacity,

No. of Cells in Parallel = Current Capacity of Pack / Current Capacity Of a Single Cell

No. of Cells in Parallel = 78.26 / 2.5 = 31.3

No. of Cells in Parallel=32//

Total No. of Cells For Battery pack = No.of cells in series * No.of cells in Parallel

Total No. of Cells For Battery pack = 70*32 = 2240//

Total No. of Cells For Battery pack =2240//

2) Energy Of a Battery Pack:

Energy of a single cell, E_cell = 8.25 Wh

Total No. of Cells For Battery pack =2240

Energy Of a Battery Pack = Energy of a single cell * No. of Cells

Energy Of a Battery Pack = 8.25 * 2240 

Energy Of a Battery Pack = 18.48 Kwh//

3)Mass of the battery pack:

It is the product of the total number of cells  and the mass of each battery cell.

Mass of Battery pack = no.of cells * Weight Of Each Cell

Mass of Battery pack = 2240 * 0.076

Mass of Battery pack = 170.24 kg//

4) Volume of Battery Pack:

It is the product of the total number of cells and the mass of each battery cell. This volume is only used to estimate the final volume of the battery pack since it does not take into account the auxiliary components/systems of the battery.

Volume of Battery pack = no.of cells * Volume Of Each Cell

Volume of Battery pack = 2240 * 0.0000344929

Volume of Battery Pack = 0.07726 m³

5) String peak Current of a cell:

It is the product of the Peak C Rate and Cell Capacity.

String peak Current of a cell = Peak C Rate * Cell Capacity

From Datasheet,W.k.t Peak C Rate =24//

String peak Current of a cell = 24 * 2.5

String peak Current of a cell = 60 A//

6) Battery peak Current :

It is the product of the No.of Cells in parallel and String Peak Current.

Battery peak Current = No.of Cells in Parallel * String peak Current of a cell

Battery peak Current = 32*60

Battery peak Current = 1920 A//

7) Battery Pack Peak Power:

It is the Product Of Battery Peak Current and Battery Pack Voltage.

Battery Pack Peak Power = Battery Peak Current * Battery Pack Voltage

Battery Pack Peak Power = 1920 * 230

Battery Pack Peak Power = 441.6 KW//

8) String Continuous Current:

It is the Product Of the Continuous C Rate And Cell Capacity.

String Continuous Current  = Continuous C Rate * Cell Capacity

From Datasheet,W.k.t Continuous C Rate =10//

String Continuous Current = 10 * 2.5

String Continuous Current = 25 A//

9) Battery pack Continuous Current :

It is the product of the String Continuous Current and No.of Cells In parallel

Battery Continuous Current = No.of Cells in Parallel * String Continuous Current of a cell

Battery Continuous Current = 32*25

Battery Continuous Current = 800 A//

10) Battery Pack Continuous Power:

It is the Product Of Battery Continuous Current and Battery Pack Voltage.

Battery Pack Continuous Power = Battery Continuous Current * Battery Pack Voltage

Battery Pack Continuous Power = 800 * 230

Battery Pack Continuous Power = 184 KW//

C) Battery Casing dimensions:

Battery Casing Dimension are calculated below:

1. Length of casing 

Length = number of cells in series x (cell diameter + margin at both side of cells ) + clearance at side 

L = 70 x (26 + 4) + 60 =  2160 mm

2. Breadth of the casing (B) 

Breadth = number of cells in parallel x (cell diameter + margin at both side of cell) + clearance at side 

B = 32 x (26 +4) + 60 = 1020 mm

3. Height of casing (H)-

Height = Height of cell + margin for wiring 

H = 65+35 = 100 mm

Here I also configure battery pack into electric vehicle lower floor panel case, a simple layout of the battery pack in an electric vehicle is shown below:

Design of cell holder (Bottom and Top):

The main function of a battery holder is to keep cells fixed in place safely and securely also it is used to keep cells in a proper arrangement so that there will be a decrease in mechanical vibration, and have a better thermal runway in between the cell gaps. Most of the cell holder is made up of polypropylene or nylon bodies rated for 80–100 °C.

Design of pack cover

Basically, Pack cover is made up of Aluminium and the reason behind is to keep battery pack for lightweight. The casing/cover thickness is 0.5 mm and the design is as shown below: A bottom cover is shown to cover below the bottom of battery Holder.

          

Design of Lower floor case for battery pack

Basically, the lower case is a part which is fitted in an electric vehicle for the assembly of the battery pack. A lower case is also made up of aluminum and it has top cover and bottom cover to battery pack from dust and environmental pollution.

The design of the lower case is shown

Install BMS for the battery pack:

Install cooling structures for air cooling/ liquid cooling

Install thermal pads for battery pack with air cooling

Battery pack with liquid cooling:

Battery pack with convection cooling structure:

RESULTS:

Calculated Parameters are Tabulated Below:

CRITERIA	RESULTS
Manufacture	A123 - Systems
Number of cells in the series	70
Number of cells in the Parallel	32
Cell energy	8.25 Wh
Battery pack energy	18.48 Kwh
Total number of cells	2240
Battery pack mass	170.24 kg
battery pack volume	0.07726 m^3
Battery pack peak current	1920 A
Battery pack peek power	441.6 kW
Battery pack continuous current	800 Ah
Battery pack continuous power	184 kW

Conclusion:

Thus,a detailed battery pack drawing along with its enclosure is Prepared And Calculated.

References:

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

2) https://datasheetspdf.com/datasheet/search.php?sWord=ANR26650M1-B