Project 1 Mechanical design of battery pack

Aim:

Mechanical Design Of Battery Pack

Procedure:

Battery pack capacity: 18 kWh

Cell: ANR26650M1-B 

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

Introduction:

Details of Battery: Nanophosphate Technology26650 Lithium Ion Power Cell-

        

                Lithium-ion 26650 cells are capable of delivering very high power due to its use of patented Nanophosphate battery technology. Based on lithium iron phosphate

chemistry(LiFePO4), the cells are inherently safe over a wide range of temperatures and conditions.Whether the application requires outstanding cycle life or stable float reliability,

the Lithium-ion 26650 cells are suitable for a wide variety of power, pulse, or stand-by applications.

     

Nanophosphate battery technology offers stable chemistry, faster charging, consistent output, excellent cycle life and superior cost performance.

It provides the foundation for safe systems while meeting the most demanding customer requirements.

Multiple layers of protection are employed at the chemistry, cell and system level to achieve an energy storage solution with superior safety and abuse tolerance compared to metal oxide

lithium-ion chemistries.

Specifications of ANR26650M1-B :

   

Applications:

1.Energy storage

2.Uninterruptible Power Supplies

3.Communication technologies

4.Aerospace

5.Electrified mobility devices

6.Industrial equipment

7.Medical devices

8.Toys

 

Theory of Battery:

what is a cell: 

A cell refers to a single anode and cathode separated by electrolyte used to produce a voltage and current. A battery can be made up of one or more cells.

A single AA battery, for example, is one cell.

   

what is Battery:

Batteries are a collection of one or more cells whose chemical reactions create a flow of electrons in a circuit.

All batteries are made up of three basic components:an anode (the '-' side), a cathode (the '+' side), andsome kind of electrolyte (a substance that chemically reacts with the anode

and cathode).

when the anode and cathode of a battery are connected to a circuit, a chemical reaction takes place between the anode and the electrolyte. This reaction causes electrons to flow through

the circuit and back into the cathode where another chemical reaction takes place. When the material in the cathode or anode is consumed or no longer able to be used in the reaction,

the battery is unable to produce electricity.

Battery Pack :

Battery packs are any number of individual batteries arranged in series or parallel to provide the required power to electronic devices.

The most common type of battery used in battery packs is lithium-ion due to its high power density.

They may be configured in a series, parallel or a mixture of both to deliver the desired voltage, capacity, or power density.

The application of battery packs is wide-ranging from phones to lawnmowers to automobiles.

Here we are using Lithium Iron Phosphate cell some considerations.

       

A.Calculation of Battery:

1. Energy = 18KWh (required)

2. Number of cells(N) = energy/(nominal voltage*capacity)

N=18000/(3.3*2.5)

N=2182

We need a minimum of 2182 cells to get 18kWh energy, now based on that, we need to decide configuration – series and parallel.

In series configuration capacity remains the same and voltage will be the sum of individual cell voltage.

In a parallel configuration, the voltage remains the same and capacity accumulates.

Let’s need 330V to run our vehicle.

The nominal voltage of one cell = 3.3V

Number of cells required to connected in series connection to produce 330V(Ns) = voltage required/nominal voltage of one cell

Ns=330/3.3

Ns=100

100 cells connected in series will generate 330 voltage and the capacity of the whole module will be 2.5Ah.

Now we need to find the number of cells which will be connected in a parallel configuration

Np(cell in parallel) = total cell / Ns

Np=2182/100

Np=21.82

Several cells can’t be infracted, so we take 22 cells for each parallel row, although it is exceeding the required capacity, that is negligible.

Cell architecture = 100Series and 22Parallel = 100S22P

3. Battery capacity 

We know parallel configured cell multiplies individual cell capacity so,

Capacity = parallel cell row*individual cell capacity

Capacity =2.5*22

Capacity = 55.0Ah

4.Current supplied by the battery

We have already calculated battery capacity which is 55.0Ah means it is going to supply 55A current per hour. which can be considered as C-rate.

5. Range

Let’s powertrain energy consumption = 129 Wh/Km at 70% powertrain efficiency

Range = Capacity / energy consumed per kilometre

Range = 18000/129

Range = 139Km

So,our vehicle will be able to cover around 139Km with current parameters.

Internal Resistance of Battery:

The entire resistance encountered by a current as if it flows through a battery from the negative terminal to the positive terminal is known as internal resistance of battery .

6.Battery Dimensions :

                                        

ANR26650 cell has 26mm diameter and 65mm height. On the basis of that we need to decide battery size of battery casing.

Length of casing(L) = number of cells at mid*(cell diameter (26) + margin at both side of cell (4)) + clearance at side (diameter of edged cell + margin)

L=98*30 + 60

L=3000mm

Breadth of casing(B) = cell diameter (26) + margin at both side of cell (4) + clearance at side (diameter of edged cell + margin)

B=20*30 + 60

B=660mm

Height of casing(H) = 65+35 (Height of cell + margin for wiring ,Cell holders and metal strips)

H=100mm

7.Weight of battery pack

Cell weight = 76g

Number of the cells = 2182

Battery pack weight(W) = cell weight*number of cells + weight of accessories

W = 76*2182 + 4.5 = 165.8 + 4.5 =170.3Kg

 

B.Battery Pack Assembly

Series /Parallel Batteries:

Battery cells can be connected in series, in parallel and as well as a mixture of both the series and parallel.

1.Series Batteries: When in a battery,positive terminal of one cell is connected with the negative terminal of succeeding cell, then the cells are said to be series connected or

simply series battery . Here, overall emf of the battery is algebraic sum of all individual cells connected in series. But overall discharged current of the battery does not exceed the

discharged current of individual cells.

  

If E is the overall emf of the battery combined by n number cells and E₁, E₂, E₃, …………… E_n are the emfs of individual cell

Similarly, if r₁, r₂, r₃, …………… r_n are the internal resistances of individual cells, then the internal resistance of the battery will be equal to the sum of the internal resistance of the

individual cells.

2.Parallel Batteries: When positive terminals of all cells are connected together and similarly negative terminals of these cells are connected together in a battery , then the cells

are said to be connected in parallel. These combinations are also referred as parallel batteries .

If emf of each cell is identical, then the emf of the battery combined by n numbers of cells connected in parallel, is equal to the emf of each cell. The resultant internal resistance of the

combination is, 

The current delivered by the battery is sum of currents delivered by individual cells.

3.Mixed Grouping of Batteries or Series Parallel Batteries: The cells in a battery can also be connected in mixture of both series and parallel. These combinations are some time

referred as series parallel battery . A load can require both voltage and current more than that of an individual battery cell.

For achieving the required load voltage, the desired numbers of battery cells can be combined in series and for achieving the required load current, desired numbers of these series

combinations are connected in parallel. Let m, numbers of series, each containing n numbers of identical cells, are connected in parallel.

    
Again assume emf of each cell is E and internal resistance of each cell is r. As n numbers of cells are connected in each series, the emf of each series as well as the battery will be nE.

The equivalent resistance of the series is nr. As, m number of series connected in parallel equivalent internal resistance of that series and parallel battery is nr/ m.  

C.Required Components of Battery Pack Assembly Tools:

Required – 2200 cells, Nickle strips, PVC heat sink film, Spot welder, Connectors, Cell holder and Solder.

Step 1: We are going to start with snapping square cell holder together. One can use cell terminal blocks, but they will consume more space than hexagonal holder.

Put insulator gasket on the positive side of cell.

   

                         Fig. Components of battery pack                                                                        Fig. Cell holder matrix

                               Fig. Cell with insulator gasket

Step 2: Now place cells in cell holder matrix. After loading all cells put second cell connector block to other side.

  

                Fig. Loded cell into holder

Step 3: Connect cell with nickel strips using spot welder. Series connection will be made by connecting cell positive to cell negative and parallel connection will be made by connecting

same terminals. Weld some nickel strips to terminal cells, which will be later used to attached balancing wire.

    

          Fig.Cell connection with Nickle strip using spot welding tool                 Fig. Connection matrix including terminasl for balancing wire

Step 4: After connections, stick PVC heat sink film to cell. solder balancing wire to terminals and battery management system’s current supply wire to battery pack.

  

                             Fig. Pack with heat sink film                                                     Fig. Soldering of balancing wire

 

                      Fig.Pack with balacing wires

Step 5: Connect balancing wire pin to BMS and glue it to side of battery pack with BMS.

  

                            Fig. Soldering of supply wires                                                             Fig.Battery pack with BMS

Step 6: Now put battery pack in an enclose, that can be made of plastic, metal or battery pack can be wrapped in a plastic sheet.

   

                            Fig. Battery in plastic case                                                                  Fig. Battery pack ready to use

Note: Pictures used in the battery pack assembly is just for understanding the purpose, they may not be relevant to battery pack calculation.

The Mechanical battery pack overall view from starting to end :

Battery Pack Enclosure View:

 

Conculsion:

Lithium Ion and Lithium Ion Polymer batteries are a great power source for projects but they require care during use and charging. They can be easy to damage or misuse and can hurt

 you/your property.