Project 1 Mechanical design of battery pack

                                                         PROJECT-1 MECHANICAL DESIGN OF BATTERY PACK

AIM:-

To develeop a battery pack of 18kw using ANR26650M1-B cell along with there machanical design.

THEORY:-

BATTERY PACK:-A battery pack is set of any number of identical batteries or inidividual battery cells.they may be configured in a series,parallel or mixture of both to deliver the desired volatge,capacity or power density.the term battery pack is often used in referenceto cordless tools,radio contrlled hobby toys,and battery electric vehicles.

components of battery packs include the individual batteries or cells,and the interconnects which provide electrical conductivity between them.rechargeable battery packs often contain a temperature sensor,which the battery charger uses to detectthe end of charging.interconnects are also found in batteries as they are the part which connects each cell,though batteries are most often only arranged in series strings.

when a pack contains group of cells in prallel there are differing wiring configurations which take into consideration the electrical balance of the circuit.battery regulators are sometimes used to keep the voltageof each individual cell below its maximum value during charging so as to allow the weaker batteriesto becomefully charged,bringing the whole pack back into balance.active balancing can also be performed by batteyr balancer device which can shuttle energy from cells to weaker ones in real time for a better balance.A  well balanced pack lasts longer and delivers better performance.

As we know that the electric vehicles market is gradually increasing.with the growth of an electric vehicle,the growth and interest in lithium-ion cells are used in aerospace,automotive electrice vehicle,mobile devices,medical devices and other electronic devices which is based on these cells.the battery pack installed in lowerfloor of the electric vehicle so that weight may distriubute equally and also the centre of gravity also maintain properly.

the high voltage battey pack is one of the most important components pf any electric vehicle.the traction battery of an electric vehicle must  achieve the following thing:

• provide maximum traction motor torque
• vehicle range in sense of kilometer
• to achieve the proper life cycle of battery

the battery pack of an electric vehicle is generally having a series or parallel combination.large battery pack have multiple cells modules.in which many number of cells are kept togeother to build a large battery pack.basically,a series connection is used to compound current capacity.a battery cell consists of five major components that are electrodes-anode and cathode,separators,terminals,electrilyte and enclosure.

Mechanical design of battery pack:

safety and reliablity are two major things for large battery packs.while mechanical designingof large battery pack we should follow some technical criteria so that the battery may not fail.

• machanical vinration should decrease
• controlling on high impact force
• better thermal runway for cooling
• serviceability and recyclability

For designing of KWh battery pack here,we use a base model of ANR26650M1B lithuim ion cell.ANR26650M1B cell consist of lithuim iron phosphate chemistry(lifePO4) and it is best for use in a wide range of temperatures and conditions.the ANR26650M1B lithuim ion cell may achieve the  following features.

• stable chamistry
• faster charging
• consistent output
• excellent life cycle
• superior cost performance.

 the provided battery cells type is ANR26650M1B and its datasheet is used to get all the required  information about it.after that,we will figure out many cells do we require to achieve the said 18KWh capacity amd also the configuration of their connection.in the end, a detailed  battery drawing along with its enclosure is given to understand the working of it more deeply.

CALCULATIONS:-

To make a battery pack, we have to  first finalze 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 18KWH=18000wh.

the individual cell=ANR26650M1-B has 

nominal voltage=3.3v

current capacity =2.5 ah

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

200 V = 33* cell in series.

cell in series =200/3.3=60.60=60

now,as we know that battery pack combiination is 60S36P

for this we decided to choose 5 series and parallel module connection.

each 5S3P configuration module voltage capacity=5*3.3=16.5 V

each 5S3P confioguration current module capacity=3.25* =7.5 Ah

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

total cells:

total number of cells= cell in module*144

total number of cells =(5*3) *144

total number of cells =2160

1 cell capacity=3.3*2.5=8.25Wh

so, the total cell capacity =2160*8.25

total cells capacity=17820Wh =17.82KWh(almost 18 KWh)

weight of one cell=76g =0.076kg

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

Module connection:

for 18Kwh of total 200V and 90 Ah battery pack capacity we need 18000/123.75=145.45 modules

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

we have to connect the cells in parallel to reach the desired capacity(mah) and connect such parallel group in series  to achieve the nimal voltage.

in this way,to achieve 200 V battery voltage number of 5S3P configuration in series connected modules are =200/16.5=12.12=12

for 90 Ah battery current,now we connected 12(90/7.5=12)times such in parallel to get 90 A current from this  battery pack.

the 5S3P connection of ANR M-B cell is shown below:

this 16.5V lithium ion battery pack has a 5S3P configuration with 7.5Ah(amp-hours)capacity.

a typical bill of materials (BOM) includes the following:-

• battery cell
• nickel or other tabbing
• PCB/PCM/BMS
• PVC shrink wrap
• insulating paper(barley paper)
• insulating foam 
• connectors and wires

Battery  pack construction:-

step 1:select the ANR26650M1-b cells for the battery pack

step2 

• before connecting the cells in parallel,first check the individual cell volatges.
• 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.
• this can damage the cells and even result in fire on rare occasions.

step 3:-assmeble the ANR26650M-B cells

• from the preivous step,it is clear that our battery pack is made up of 3 parallel groups connected in series and each parallel group have five cells.
• now we have to arrange the cell 15 cells properly for making the electrical connection among them and with the BMS board.
• palce the first parallel group of cells(5nos) positive side up,then place the second parallel group  negative side up and then finally the last parallel group positive side up.
• we can assemble the cells to  make the pack by using hot glue or by using plastic 18650 battery holder.We used the plastic the ANR2665M1-B cell holders/spacers to assemble 15 cells.
• it provides spaced between the cell which allow fresh air to pass and the battery get cooled easily.
• it also makes a battery pack solid and relaible and provide safety antivibration to our battery pack.

Step 4: choosing the right battery strips and spot weld the neickel strips

we have two options to connect the ANR2665M1-B cells togeother

• soldering
• spot welding 

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

• to  make the battery pack,we have connect the ANR2665M1-B cells togeother by means of nickel strips ot thicker wire.
• generally,nickel strips are widely used for this.
• in general,two types nickel strips are available in the market nickel-plated steel strips and pure nickel strips.
• the pure nickel is little bits costleir than the nickel-plated steel,but it has much lower resistance means,low resistance means less heat generation during the charging and discharge which leads to longer useful battery life.

step 5:adding the BMS

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

• monitors all the parellel groups in the battery pack and disconnect it from the input power source when fully charged.
• balance all the cells voltage equally 
• doesn't allow the pack from over-discharged.

step 6:Install cooling structures for air cooling or liquid cooling 

step 7:Install the battery pack inside the enclosure 

the battery pack have all around exposed nickel strips,to avoid any accidental shorting an enclosure used.