Project 1 Mechanical design of battery pack

Ans)

Mechanical design of a battery pack :-

One of the fundamental components of an electric powertrain is the battery pack. The battery pack is the energy source for the vehicle, and for high-performance vehicles, it must supply energy to the vehicle at very high power. The automotive environment is especially challenging for batteries, as the batteries are subject to a wide range of operating conditions. Thermal considerations are critical to the safety and performance of battery packs, a challenge that is intensified in cars because of the increased heat generation in batteries at high charge and discharge rates, which are necessary for high power output. Mechanical robustness is also a critical challenge, the battery pack must not only be able to withstand vibration and loads from normal driving conditions and accelerations and decelerations, but also maintain structural integrity in crash scenarios. This is especially important for safety because impac lithium ion batteries can be extremely dangerous and cause catastrophic failure of the entire battery pack.

A battery pack is a set of any number of (preferably) identical batteries or individual battery cells. They may be configured in a series, parallel or a mixture of both to deliver the desired voltage, capacity, or power density. The term battery pack is often used in reference to cordless tools, radio-controlled hobby toys, and battery electric vehicles.

Cells :-

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.

Cell: ANR26650M1-B Datasheet .

Li-ion cell(ANR26650M1-B):

This Li-ion cell is manufactured by Lithiumwerks.They deliver very high power due to their use of patented Nanophosphate battery technology.

Based on the Lithium iron phosphate chemistry (LiFePO4),the cells are inherently safe over a wide range of temperature and conditions, For outstanding cycle life,stable float reliability this cells are suitable for a wide varity of power,pulse and stand by applications.

Nanophosphate battery technology offers thermal stable chemistry,fast charging.consistent output,low capacity loss over time. It provides extremely safe conditions for while meeting most demanding customers requirements.Multiple layers of protections are employed on chemistry.cell and system level to acheive an energy storage solution with superior safety.

Electrical Configuration :-

Single cell has voltage of 3.3V and 2.56Ah of ratings.

Capacity of single cell :-

3.3V*2.56Ah = 8.448 watt hour

Assuming Battery pack voltage of 330 V.

Series connection of cells:-

Each cell voltage is 3.3V and pack voltage should be 330 Volt, therfore 100 cells are needed to be connected in series.

Ns = 330/3.3 = 100 cells.

Parellel connection of cells :-

Required capacity is 18000wh

As voltage is assumed to be 330 V

Therfore current output at terminals of battery pack is

18000/330 = 54.54Ah.

Single parallel path produces 2.56Ah,

Therfore,

54.54/2.56 = 21.3 = 22(approximately) parallel connections are required.

Total Number of cells are:-

Number of cells in series mulipiled by number of cells in parallel 100*22 = 2200 cells are required.

Cell architecture 100 Series and 22 Parallel = 100S22P

Mechanical design of battery pack :-

length of cell is 66mm

diameter of cell is 26mm

Module:-

To increase cell ratings , same types of cells are connected in series and parallel.

Extra 2mm length is taken for cell strips and distance between cells assume to be 4mm. Assuming 25 cells are connected in series in module.

Therefore,rating of cell is

Voltage = 25*3.3 = 82.5V

Ampere hour remains constant as cells are connected in series.

Therefore, One module consists of 25 cells.

Total modules = 2200/25 = 88

If we connect four modules in series, It deliver 330V and 2.35Ah and here it form one parallel path.

Each parallel path consist of four modules and these should be repeated for remaning 22 parallel paths.

If connect 88 modules then it will become battery pack.

This is one of the module configuration. Other module configurations are also possible.

Connections of cells :-

Cell are connected with the help of Nickel strips as shown in below figure.

Nickel strips are used because of their heat capablities.

Welding:-

To connect cells the nickel strips are used. Welding has to be done to connect cell to nickel strip.

Types of welding are

1. Spot Weld

2. Laser weld

3. wire bond

Calculating volume and weight of a module :-

considering Protection Venting, Nickle strip and Foil based component and battery the Length is 70mm.

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

L=[100*(30)]+60

L = 3060mm

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

B=[22*(30)]+60

B = 720mm

Height of casing (H) = 66 + 35 (Height of cell + margin for wiring Cell holders and metal strips)

H = 101mm

Weight of battery pack

Cell weight = 76g

Number of the cells = 2200

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

W=76 * 2200 + 4.5

W =167200 + 4.5

W =167.2 kg

Above fig. shows the total battery pack.