Project 1 Mechanical design of battery pack

Aim - Prepare a detailed battery pack drawing along with its enclosure by stating assumptions.

Theory -

Battery Pack Cell type - ANR26650M1-B

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.

Calculation of battery pack is as follows -

1. Volume of each cell :

Dimention = 26x65mm

`v = pi r^2h`

so, `v = pi*13^2*65` = 35mm3.

2. Battery Cell Energy :

Energy = Voltage * Capacity

E = V*C = 3.3V * 2.5Ah

E = 8.25Wh

3. Battery Pack :

The total energy required is 18KWh.

Converting KWh to Wh i.e., 18000Wh.

4. Number of cells in Series :

Let us assume that the battery pack voltage which is required to be 330V and the nominal voltage of the battery as per the datasheet is given as 3.3V.

To find total number of cells in series :

total cell voltage/single cell voltage = 240/3.3 = 72.72, or 73

cells in series = 73

5. Number of cells in Parallel :

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

And we assumed 240 Volts are need to run the vehicle.

The capacity of the total battery for 18kWh is,

Capacity = 18000/240 = 75, or 75Ah.

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

No. of cells in parallel = 75/2.5 = 30 cells.

6. Now the total power of a battery module :

(cells in series*nominal voltage) * (cells in parallel*nominal current) = (73*3.3V)*(30*2.5Ah)

total power = (240.9)*(75)

total power = 18067.5Wh or 16KWh.

7. Cell model :

The total cell model is having the pack of 73S30P configuration i.e., 73 series, and 30 cells connected in parallel

So, total number of cells = 2190 cells

Mechanical Design of Batterty Pack :

Component of the battery pack

1. 2190 cells
2. Nickel strip
3. 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.

Gasket insulator :

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

Now we will be soldering the battery wire

Step 5 -

Connect the balancing wire pin to the battery management system.

Battery Types and Welding Methods

The connecting process is a challenge because it combines highly conductive materials that vary in thickness. The common energy storage methods include lead-acid, nickel-cadmium, nickel-metal hydride, sodium-nickel, and lithium-ion batteries. Usually, spot welding, projection welding, or ultrasonic and laser welding are used to combine batteries, with spot welding being the most common method.

How does it Work?

The first takeaway of battery spot welding is that the process does not need any filler material. It involves pressure and heat applying to the welding area. A copper-alloy electrode transmits current through the material so that it melts and fuses the parts. The current is off while the pressure maintains to solidify the weld and so the joint forms. Usually, the current only runs in a flash whereas the pressure stays a bit longer

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.

1. Length of casing

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

L = 73 x (26 + 4) + 60 = 2250 mm or 2.25m

2. Breadth of the casing (B)

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

B = 30 x (26 +4) + 60 = 960 mm or 0.96m

3. Height of casing (H)-

Height = Height of cell + margin for wiring

H = 65+35 = 100 mm

4. Weight of the battery :

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

W = 76*2190 + 4.5 = 166.44 + 4.5 = 170.94kg

Battery Management System :

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 any damages which leads to explode at critical situations.

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.

Conclusion -

So the design calculation for the battery pack was carried out. The steps involved in the making of the battery pack have been listed out