Project 1 Mechanical design of battery pack

CHARGE/DISCHARGE

While the battery is discharging and providing an electric current, the anode releases lithium ions to the cathode, generating a flow of electrons from one side to the other. When plugging in the device, the opposite happens: Lithium ions are released by the cathode and received by the anode.

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.

Nanaophosphate High Power LithiumIon Cell ANR26650M1-B

A123’s high-performance Nanophosphate® lithium iron phosphate (LiFePO4) battery technology delivers high power and energy density combined with excellent safety performance and extensive life cycling in a lighter weight, more compact package. Our cells have a low capacity loss and impedance growth over time as well as high usable energy over a wide state of charge (SOC) range, allowing our systems to meet end-of-life power and energy requirements with minimal pack oversizing.

Applications of the battery.

There are various applications of Lithium-ion cells

1. COMMERCIAL SOLUTIONS

This is a large-scale application for the battery where high power is required.

• Datacenter UPS
• Telecom backup
• IT backup
• Autonomously guided vehicles
• Industrial robotic and material handling equipment

2. GOVERNMENT SOLUTIONS

• Military vehicles
• military power grids

3. GRID SOLUTIONS

• Frequency regulation
• Renewable integration
• REverse capacity
• Transmission and distribution

4. TRANSPORTATION SOLUTIONS

• Plug-in hybrid vehicles, hybrid cars, electric vehicles
• Commercial vehicles
• Off-highway vehicles
• passenger vehicles.

The performance of the cell is given in the datasheet that is referred to for this project.

These images show the power discharge, current discharge, and the life cycle of the cells used for the battery pack.

Here you can see the voltage capacity of the battery for different power ratings.

DESIGN CALCULATION

All the parameters of this calculation are taken from the datasheet

PROCEDURE FOR THE CALCULATIONS-

The capacity of the battery pack is set to be 18kWh.

For making a high voltage battery pack many cells are arranged in a particular pattern and sequence to improve the voltage and the power rating.

Individual battery cells may be grouped in parallel and/or series as modules. Further, battery modules can be connected in parallel and/or series to create a battery pack. Depending on the battery parameters, there may be several levels of modularity.

The total battery pack voltage is determined by the number of cells in series. For example, the total (string) voltage of 6 cells connected in series will be the sum of their individual voltage.

In order to increase the current capability of the battery capacity, more strings have to be connected in parallel. For example, 3 strings connected in parallel will triple the capacity and current capability of the battery pack.

Now for calculating our required battery pack based on the cell manufacture data provided.

The calculation for the battery pack is as follows.

ANR26650M1-B Specifications
Nominal Ratings
Voltage: 3.3 Volts
Capacity: 2.5 Ah
Energy: 8.25 Wh
Specific Power: 2600 W/kg
Impedance (1KHz AC Typical) 6 mΩ
Cycle Life at 1C/1C, 100% DOD: > 4000 cycles
Cell Type: 26650 Lithium Ion Power Cylindrical Cell

Discharging
Max Continuous Discharage: 50 A
Max Pulse Discharge Current >50% SOC (10s): 120 A
Minimum Voltage: 2 Volts
Temperature: -30ºC to 55ºC

Charging
Recommended Standard Charge: 2.5 Amps
Max Charge Rate: 10 Amps
Max Pulse Charge Current <50% SOC (10s): 25 A
Float Voltage: 3.45 Volts
Recommended charge V & Cut-off Current: 3.6 Volts, taper to 125mA
Temperature
(reduce charging current to 250mA when under 0ºC): 0ºC to 55ºC

Mechanical
Diameter: Ø25.96 +/- 0.5 mm (1.0")
Length: 65.15 +/- 0.5 mm (2.6")
Mass: 76 g

Calculation as per assumptions:- 18kWh Battery Pack

calculation for designing an 18kWh battery pack, basically 18kWh is energy require to achieve the vehicle its proper range. It is depending upon the voltage (V) parameter and ampere-hour or capacity (Ah).

Here we design a high voltage battery pack for an electric vehicle to achieve its range up to 220 km.

For this calculation, I assumed 145.2 V a nominal voltage for series connection.

Basically, the value of the volume of the cell is used to find out the total volume of the battery pack.

Single Cell Energy (Wh)

= Cell Capacity (Ah) x Cell Voltage (V)

= 2.6 x 3.3

Single Cell Energy (Wh)= 8.58 Wh

The value of a single cell is used to calculate the total energy of the battery pack.
-Single Cell Energy Density

Volumetric energy (Wh/m^3) = Single Cell Energy / Volume of each cell

= 8.58 Wh / 0.03451 m^3

= 248.62 Wh/m^3

Gravimetric energy (Wh/kg) = Single Cell Energy / Single Cell Mass

= 8.58 Wh / 0.076 kg

= 112.89 Wh/kg

Calculation of High Voltage Battery Pack
For design and calculation of battery pack here, I assume a vehicle to achieve 250 km in 18 kWh battery pack. Also, I assume 145.2 nominal voltage for series connection.
So,

Vehicle Range = 250 KM (assumed)
Battery Pack capacity = 18.121 kWh or 18120.96 Wh (For better and accurate calculation here I change kWh)
Now,
We will calculate per km average energy = 18120.96 / 250
= 72.483 Wh/km

Therefore,
Battery Pack total energy = Average energy x km
= 72.483 x 250
= 18120.96 Wh or 18.120 kwh

Let’s assume Nominal voltage for series connection = 145.2 V, Basically, this depends upon the motor power, We can decide the value according to the motor.

Number of cells connected in series

= Nominal voltage of series connection / Nominal voltage of a single cell
=145.2 V / 3.3 V
= 44

44 Cells will be connected in a series connection to provide a proper voltage.

- Energy for battery pack (wh)

= No. of cells connected in series x Single-cell energy

= 44 x 8.58 wh

= 377.52 wh

-- Number of cells connected in parallel

= Battery pack total energy (wh) / Energy for battery pack (wh)

=18120.96/377.52

= 48

48 cells will be connected in parallel to provide a proper capacity power.

-- Battery pack total energy (wh)
= No. of cells connected in parallel x Energy for battery pack (wh)
= 48 x 377.52
= 18120.96 wh or 18.120 kWh

-- Battery pack capacity
= No. of cells connected in parallel x Single cell capacity (Ah)
= 48 x 2.6 Ah
= 124.8 Ah

The value of battery pack capacity is used for the total power required by the vehicle.
-- Total number of cells for battery pack

= No. of cells connected in parallel x No. of cells connected in series

=48x44

= 2112

2112 Cells will be used to make a complete battery pack.
-- Mass of battery pack

= Total no. of cells for batter pack x Mass of single cell

= 2112 x 0.076 kg

= 160.512 kg

it is the total weight of cells connected in parallel and series.

-- Total volume of the battery pack
= Total no. of cells for batter pack x Volume of single cell
= 2112 x 0.0345
= 72.89 m^3

This is the volume of2112 cells which are used in the battery pack system.

-- Cell peak current (A)
= C rate (Max Pulse Charge Current) x Single cell capacity
= 20 x 2.6
= 52 A

-- Battery pack peak current (A)
= Cell peak current x No. of cells connected in parallel
=52X48
= 2496 A

It is used for the operation of the battery pack. By this way, a vehicle will decide how much power is required to move.

-- Battery pack peak power (W)
= Battery pack peak current x Voltage of series connection
= 2496 A x 145.2
= 3624192 or 362.42 W

-- Cell continuous current (A)
= Crate (Max Continuous Charge Current) x Single cell capacity
= 10 x 2.6
= 26 A

-- Battery pack continuous current (A)

= Cell continuous current x No. of cells connected in parallel

= 26 x 48

= 1248 A

This is the power which is supply continue to the whole battery pack system.

-- Battery pack continuous power (W)

= Battery pack continuous current x Voltage of series connection

=1248 x145.2

= 18120.96 or 18.120 Kwh

detailed battery pack drawing along with its enclosure.

Battery dimensions-

1. Length of casing

length = number of cells x (cell diameter + margin at both side of cells ) + clearance at side

L = 100 x (26 + 4) + 60 = 3060 mm

2. Breadth of the casing (B)

Breadth = number of cells x (cell diameter + margin at both side of cell) + clearance at side

B = 22 x (26 +4) + 60 = 720 mm

3. Height of casing (H)-

Height = Height of cell + margin for wiring

H = 65+35 = 100 mm

Assembly of the battery pack

Component of the battery pack

1. 2200 cells
2. Nickel strip
3. PVC heat sink film
4. spot welder
5. Connected
6. Cell holder
7. Solder

Step 1 -

The first step is to start snapping the square cell holder together. One can use the cell terminal block but they will take more space than a hexagonal block.

this is the cell holder block

This image shows the insulate gasket

Step 2 -

Placing the cells in the holder matrix. Place all the cells in the holder and put the second holder in the place.

Step 3 -

Now we will be connecting the cells with nickel strips using the spot welding process. The series connection will be made by connecting the positive terminal of the cells to the negative terminal. The parallel connection will be made by connecting the same terminal.

Connecting the complete matrix of the cell together.

Step 4 - Connecting the heat sink to the battery pack

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Now we will be soldering the battery wire

Now the internal structure of the battery pack is assembled and all the terminals are connected as per the connections.

Step 5 -

Connect the balancing wire pin to the battery management system.

Step 6

After the battery management system, the next and final step is to place the enclosure for the battery pack.

This is the final battery pack model created.

CONCLUSION

The design calculation for the battery pack was carried out and calculated and a table has been made for the same. The steps involved in the making of the battery pack have been listed out.

REFRENCE:

https://x-engineer.org/ev-design-battery-calculation/