Mechanical design of 18kwh battery pack

AIM:

To model a battery pack of 18kwh energy using ANR26650M1-B cell.

 Procedure:

# ANR26650M1-B cell datasheet is used to refer to the data for energy calculations.

# Once calculation for no. of. cells to be used for building an 18kwh energy battery pack is done then the cad software is used.

# Here Solidworks software is used to build the model. 

# IV, INDIAN VERNATION is the name used here for the model build.

Introduction for the 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), and some 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:

# 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 for radio-controlled 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 detect the end of charging. Interconnects are also found in batteries as they are the part that connects each cell, though batteries are most often only arranged in series strings.

# An advantage of a battery pack is the ease with which it can be swapped into or out of a device. This allows multiple packs to deliver extended runtimes, freeing up the device for continued use while charging the removed pack separately.

# Another advantage is the flexibility of their design and implementation, allowing the use of cheaper high-production cells or batteries to be combined into a pack for nearly any application.

# At the end of product life, batteries can be removed and recycled separately, reducing the total volume of hazardous waste.

Some basic terms related to the Battery:

# Voltage:

Total voltage, voltages of individual cells, minimum and maximum cell voltage, or voltage of periodic taps. To maximize the battery's capacity and to prevent localized undercharging or overcharging, the BMS may actively ensure that all the cells that compose the battery are kept at the same voltage or the State of charge, through balancing.

# Temperature:

Average temperature, coolant intake temperature, coolant output temperature, or temperature of individual cells.

# State of Charge(SOC):

Depth of charge(DOD) to indicate the charge level of the battery.

# State of Health(SOH):

A variously defined measurement of the remaining capacity of the battery as % of the original capacity.

# State of Power(SOP):

The amount of power available for a defined time interval given the current power usage, temperature, and other conditions.

# Current:

Current in or out of the battery.

Cell specification:

Calulations:

1. Total energy needed = 18kwh (or) 18000wh

2. Cell voltage = 3.3V

3. Cell capacity = 2.5Ah

# A module is designed in the configuration of 3s 5p

# Series connection of a module = No. Of. cells x single cell voltage

# Series connection of a module = 3 x 3.3

# Series connection of a module = 9.9V

# Parallel connection of a module = No. Of. cells x single cell capacity

# Parallel connection of a module = 5 x 2.5

# Parallel connection of a module - 12.5Ah

# Energy capacity for a single module = 9.9 x 12.5

# Energy capacity for a single module = 123.75wh

Let us consider the pack voltage is 69V

# NSM = Pack Voltage/Series connection of a module

# NSM = 69/9.9

# NSM = 7 Modules in the series placement of the battery pack

# Pack energy = Total energy/pack voltage

# Pack energy = 18000/69

# Pack energy = 261Ah

# NPM = Pack energy/parallel connection of a module 

# NPM = 261/12.5

# NPM = 22 modules in the parallel placement of the battery pack

Cell:

# Total no. of cells in the battery pack = 7 x 22 = 154 modules

# Total no. of cells in the module = 3 x 5 = 15 cells

# Total no. of cells in the battery pack = 154 x 15

# Total no. of cells in the battery pack = 2310 cells

Mechanical Design:

step 1: Drawing cell model

# The dimensions of the cell are 26650 given in the datasheet. 

# 26mm is the diameter of the cell & 65mm is the height of the cell are the dimensions used to draw the cell.

Step 2: Module Assembly

The cells are arranged in 3s5p. For the space storage and neat connection of cells, the position of the middle cell is changed the negative terminal is kept upwards.

Step 3: Making of the spacer model

# Spacer is used to separate the cells for air ventilation with a minimum gap of 1mm.

# Here carbon fiber material is used for weight reduction and for maintaining strength. The manufacturing method is made up of 3d printing.

Step 4: Connectors assembly with the module and spacer 

# The cells are placed in the spacer and the module is made.

# Where at the top of the cells a connector is used for the connection.

# The connector is called the nickel strip. By using the welding process the strips are welded on the battery terminal.

# For a series connection in a row a positive terminal and negative terminal are connected in each row. 

# For parallel connection first column of the cells is connected with all positives and the third column cells are connected with all the negatives. That is the positive and negative terminal of a module.

These are the two types of connectors used in this battery pack design.

Step 6: Module holder making

# The part is named module holder.

# There are 154 modules in this pack for maintenance purposes the holder is created for user-friendly to identify the module problem and to replace it without affecting any damage to the other module.

Step 7: Module assembly with the holder

The modules are placed inside the module holder.

Step 8: Battery enclosure model making

# Battery pack cover labels with IV 2310C154M3S5P which denotes

IV - Manufacturer name

2310C - NO.OF.CELLS

154M - NO.OF.Modules

3s5p - Cell connection in the module

Exhaust fans are used for ventilation purposes to regulate the airflow for the safe working of the battery.

Step 9: Complete assembly of 18kwh battery pack

# The final assembly of 18kwh battery pack. The red and green pins are the positive and negative terminal of the pack

# The overall dimension of the battery pack is 1043m.m Length x 996mm Width x 120mm Height

The total energy of the pack actually used is = pack voltage x pack energy

pack energy = 12.5 x 22modules =275Ah

The total energy of the pack actually used is = 69 x 275

The total energy of the pack actually used is = 18975wh (or) 18.9kwh