Project 1 Mechanical design of battery pack

AIM:

To Prepare a detailed battery pack drawing along with its enclosure with ANR26650M1-B by a capacity of 18 kWh.

 ANR26650M1-B is a Nano phosphate high power lithium-ion cell which is made by lithium iron phosphate (LiFePo4). This is more power and have high energy than other cells and lower impedance it has high efficiency with more safety precautions also having long life. It has wide range of SOC with less losses which leads to less discharge for long range with lighter weight. These cells have low-capacity loss and impedance growth over time as well as high usable energy over wide state of charge range.

It is widely used in all areas which have necessity of high power and energy as, transmission and distribution, grids, power plants, EV and HEV vehicles, military machines and vehicles. And it uses also in system back-ups, industrial robotics, medical devices etc.

The view of the ANR26650M1-B is as shown below, by the A123 systems manufacturer.

 

The parameters of the ANR26650M1-B is as shown,

From this we can say that the nominal voltage is 3.3V, cell capacity 2.5Ah

If we observe the characteristics of the ANR26650M1-B by different conditions like constant power discharge characteristics, constant current discharge at various temperatures, and some other as shown below,

If we observe here that by changing the power that is by increasing the power at constant temperature it decreases the voltage respectively.

If we observe here by changing the temperature from 45 degrees to – 15 degrees  it reduce respectively as shown above.

In this as we can see that by changing the charging and discharging cases as shown its performance characteristics changed her (+) represents charging and (-) represents discharging. By changing the temperatures its performance change.

Design of the ANR26650M1-B cell with dimensions as shown below,

 

As we know that the safety, designing, sizing and some other things are more important to any of the object they play the key role for the transport, manufacturing etc. if we see these aspects in the lithium-ion cell batteries it is difficult to transport the battery because of the vibrations, exposure of high impact of the forces and thermal run away. To avoid all these to small the robust mechanical designs are necessary. Here the mechanical designs are play a major role before using in the vehicles or some others machines because if any problem occur in the designing time it leads to damage the battery or creates a major problem in the circuit. In the designing battery packing provide a greater degree of protection against so many of these.

Basic design of the cells.

The major parts off the battery cell are five those are, anode, cathode, separators, electrolyte and terminals. A battery consists of one or more electro chemical cells (battery cells) which are converting chemical energy into electrical energy at the time of discharging and electrical energy to chemical at the time of charging. The chemical reaction occurs at the time of charging and discharging is called chemistry of the battery. There are so any types of cells in use like cylindrical, flat, pouch etc.

A battery has a set of modules which is be in certain design with set of cells connected. The modules and batteries are connected or configured in a series, parallel or in both based in the requirement by this the outlook of the battery pack is decide. By changing the same cells with different design changes the voltage and capacity values but the power remains same in the circuit. The battery pack consist both hardware and software components which is cell and BMS respectively.

The inner parts of the battery pack are shown above by collecting all these software and hardware parts a complete battery pack be form. By changing the cell connections, the outlook be change but the parts and its functions are be same. The design of the battery is decided before the construction based on the palace available in the vehicle to fit.

The performance characteristics and other view of the ANR26650M1-B are,

By this we can identify or observe the overall view and its specifications be known.

In this graph if we see that the points in the line indicate the percentage of 25% each. In the specific energy line, it shows 2 points which is 50% of energy be given on our requirement. In the specific power it shows full that is it gives the 100% of power as an output from the battery. In the safety point of view also it gives 100% to protect. But in performance issue it gives only 50% from its life. It has 100% life span which is given by the manufacturer and its cost also less and easy to buy for the consumers.

Building steps of the battery pack:

Parts of the battery

The main parts of the battery system are, cells, modules, BMS, wires, strips, case, separators, insulators, sensors etc.\

The complete manufacturing processes of the battery pack look like as shown.  

These are the equipment’s that is used to complete the total battery pack through the machines.

The machines that we used for the battery packing are,

• Auto sticker machine, auto sorting machine, spot welding machine, shrinking machine, code printing machine, and aging machine.
• Auto sticker machine is used to stickering the names that is labelling to the cells based on the given values its condition and some other parameters basses.
• The sorting machine can execute the sorting test based on the voltage and internal resistance tests before assembly. the battery sorter machine has 8 channels for OK battery cells and 1 for NG battery cells, which greatly promote the sorting efficiency and ensure the normalization of cells sorting.
• To build the battery pack the cell parameters its working and mechanical design are very important. The battery calculations are used to build the pack with specific idea based on our requirement. By this we can find the exact size, its location, necessary of the cooling system etc can be find.

 Battery calculations.

Given data

Battery energy = 18 kWh

From the ANR26650M1-B data sheet

Nominal voltage = 3.3 V

Cell capacity = 2.5 Ah                  

Internal impedance = 6 mΩ

Cell weight = 76 g

Cell Dimensions = 26*65 mm

Operating temperature = -30°C to 55°C

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

N = 18000 / (3.3*2.5)

N = 2182 cells nearly

We need minimum of 2182 cells to get 18 kWh energy, now based on that, we need to decide configuration – series and parallel but it not exact cells.

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.

And we assumed 300 Volts are need to run the vehicle.

The capacity of the total battery for 18kWh is,

Capacity            = 18000/300

Battery capacity = 60 Ah

The nominal voltage of one cell is 3.3V.

Number of series cells required to produce 300 V (Ns) = voltage required / nominal voltage of one cell

Ns = 300/3.3

Ns = 90.9

Ns = 91 cells in series

So, to produce 300 V of voltage we require 91 cells of ANR26650M1-B in series which having 3.3V. the excess of voltage be consider in losses.

The capacity of the whole module will be 2.5

To find the number of cells which will be connected in a parallel configuration

Np = 60 / 2.5

Np = 24

Np = 24 cells in parallel

Here we use 24 cells are in parallel to run the battery with 60 Ah capacity.

The total cell model is having the pack of 91S24P configuration

• The spot-welding machine has anintelligent welding function which can improve the efficiency of the battery pack during the welding process. It’s equipped with built-in temperature sensors and an intelligent cooling system which can automatically work according to machine’s internal temperature. It is used to weld the strips which is used to connect the cells for series a parallel.

Battery module:

The total battery power = (91*3.3 V) * (24*2.5 Ah)

                                      = 18018 Wh

                                      = 18.018 kWh

The battery requirement is 18.018 kWh battery pack, the required configuration of that pack is 91S24P, i.e., 91 series, and 24 cells connected in parallel

To build such a large grid, we need to slip the battery packs into the battery module, which reduce the complexity of monitoring and optimising battery management and minimizing battery damage.

For that we use the modules which take care of cells protection, monitoring, connections of set of the cells.

In this we are dividing the set of cells from battery pack 91S24P into 7S4P

So, the no of cells in each module are = 7*4

                                                            = 28 cells

Total no of cells = 2184 cells

Therefore, no of modules = 2184 / 28

                                         = 78 modules

We have already calculated battery capacity which is 60 Ah means it is going to supply 60 A current per hour. which can be considered as C-rate of the battery.

Let us assume the energy consumption for 1 km is 100 Wh. So, the total range of the battery for 18kWh is 180 Km.

There fore the no of kilometres that a vehicle run with full charge of 18kWh is 180Km.

Battery enclosure pack size:

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

Length of casing (L) = number of cells at series*(cell diameter (26) + margin at both side of the cell which to free up space called holders and gaps for the sheet protectors etc (4) + clearance at side (diameter of edged cell + margin) (All should be in value with mm)

L = 91*30+80

L = 2810 mm

Cells in series

Cell holders,

Breadth of casing (B) = number of cells at parallel*(cell diameter (26) + margin at both side of the cell (4) + clearance at side (diameter of edged cell + margin) for protection

B = 24*30 + 80

B = 800 mm

Cells in parallel,

Side clearances,

There fore the total area of the battery is = 2810 * 800

                                                                 = 224800 mm

                                                                 = 2.248 m

Height of the battery (H) = 65 (height of the cell) + 35 (wires, holders, strips etc)

                                         = 100 mm

Therefore, the volume of the battery is = L*B*H

                                                            = 2810*800*100

                                                              = 0.224 m

Weight of battery pack

Cell weight = 76g from data sheet

Number of cells = 2184

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

W = 76*2184 + 4.5 = 165.984 + 4.5 = 170.48kg     

Here we got the battery sizes its weight, no of cells and modules, pack size with its accessories like wires etc.

The Battery Management System (BMS) is connected to the cells modules and battery which is used to identify the critical situations like the voltage, temperature, battery capacity values at the running of the battery time. It is mainly used for the monitoring purpose and balancing of the cells in the battery pack. By this we can operate with out and damages which leads to explode at critical situations. The outlook of the BMS with the cells look like as shown.

shrinking machine is used to shrink the battery pack with certain heated temperature in the form of air in the closed loop. The code printing and the aging machine are used to print he code value of the battery cell like ANR26650M1-B and life time of the battery be calculated respectively.

The testers are used to confirm the cell total parameters like voltage, capacity, temperature, pressure, BMS, chemicals etc.