Project 1 Mechanical design of battery pack

                                                          EV LIVE BATCH -16

Battery pack capacity: 18 kWh

Cell: ANR26650M1-B 

Prepare a detailed battery pack drawing along with its enclosure. State your assumptions..,,??

SOLUTION :

TO MAKE THE BATTERY PACK, WE HAVE TO FIRST FINALIZE THE NOMINAL VOLTAGE AND CAPACITY OF THE PACK.

EITHER IT WILL BE IN TERM OF VOLT,MAH/AH OR WH..

Total required Battery pack capacity is 18000wh

The individual cell: ANR 26650M1-B 

Nominal voltage =3.3v

Current capacity=2.5Ah

so,let us assume that for 18kwh battery pack we need supply voltage of 200v and 90Ah

200v=3.3*cell in series

cell in series =200\3.3 = 60.60=60

NOW ,AS WE KNOW THAT BATTERY PACK CAPACITY (WH)= TOTAL CURRENT*TOTAL VOLTAGE =(2.5 cell in parallel) *200

CELL IN PARALLEL = 18000/(2.5*200)=36

MODULE CAPACITY :

The required battery pack combination is 60s36p

For this we decided to choose 5 series and 3 parallel module connection 

Each 5s3p configuration module voltage capacity =5*3.3=16.5v

Each 5s3p configuration module  curent capacity = 3*2.5=7.5Ah

so,total capacity of 1 module is = 16.5* 7.5=123.75wh

Total cells:

Total number of cells = cell in 1 module *144

Total number of cell = (5.3)*144

TOTAL NUMBER OF CELLS =2160

1 cell capacity = 3.3*2.5=8.25wh

so,total cell capacity =2160*8.25

TOTAL CELLS CAPACITY =17820 Wh = 17.82kwh(almost 18Kwh)

NOTE: WE SHOULD ALWAYS TARGET MORE KWH THEN REQUIRED CONSIDERING THE LOSSES AND CONNECTION LIMITATIONS,

weight of one cell= 76g=0.076kg

so,battery pack cell weight = 0.076*2160=164.16kg

MODULE CONNECTION:

for 18kwh of total 200v and 90kwh battery pack capacity we need 18000/123.75= 145.45modules

for simplicity of configuration we took 12*12 =144 modules of 5s3p

in this way , to achieve 200v battery voltage ,number of 5s3p configuration in series connected modules are = 200/16.6=12.12=12

For 90Ah battery current ,now we connected 12(90/7.5)=12 times such (series of 12 module of 200v) in parallel to get 90A current from this battery pack

The 5s3p connection of ANR26650M1-B CELL :

This 16.5v lithium ion battery pack has a 5s3p configuration with 7.5Ah (amp -hours )capacity

A TYPICALLY BILL OF MATERIAL (BOM) INCLUDES THE FOLLOWING:

• Battery cell 
• Nickel or other tabbing 
• PCB /PCM /BMS
• PVC shrink wrap
• insulation paper 
• insulation foam 
• connectors and wires

STEP-01 SELECT THE ANR 26650M1-B CELLS FOR THE BATTERY PACK 

STEP-02 CHECK THE CELL VOLTAGE

• Before connecting the cells in parallel,first check the individual cell voltage 
• For paralleling the cells, the voltage of each cells should be near to each other, otherwise a high amount of current will flow from the cell with higher voltage to the cell with lower voltage 

STEP -03 :ASSEMBLE THE ANR 26650M1-B CELLS:

• From the previous step, it is clear that our battery pack is made up of 3 parallel groups connected in series and each parallel group have 5 cells
• now we have to arrange the 15 cells properly for making the electrical conection among them and with the BMS board 
• it provides space between the cells which allow fresh air to pass and the battery get cooled easily
• it also makes our battery pack solid and reliable and provide safety anti vibration to our battery pack.

STEP-04: CHOOSING THE RIGHT BATTERY STRIPS AND SPOT WELD THE NICKEL STRIPS:

We have two options two connect the ANR26650M1 -B cells together:

1. soldering
2. spot welding

• the best choice is always spot welding ,but spot welder is much costlier than a good quality soldering iron.

• To make the battery pack,we have to connect the ANR 26650M1 -B cell together by means of nickel strips or thick wire
• In Generally, two types of  nickel strips are available in the market : nickel -plated steel strips and pure nickel strips

STEP-05 : ADDING THE BMS,

A battery management system ( BMS) is any electronic system that manages a lithium battery pack and the main functionalities are:

• Monitors all of the parallel groups in the battery pack and disconnect it from the input power source when fully charged
• balance all the cells voltage equally 
• doesnt allow the pack from over-discharged

THE BATTERY PACK HAVE ALL ROUND EXPOSED NICKEL STRIPS ,TO AVOID ANY ACCIDENTAL SHORTING AN ENCLOSURE USED...