Project 1 Mechanical design of battery pack

Mechanical design of battery pack :-

To make the battery pack, we have to first finalize the Rated Capacity of the battery pack with the help of given below Datasheet

Total required Battery pack capacity is 18 kWh.

The individual Cell: ANR26650M1-B has

Nominal voltage = 3.3 V

Current Capacity = 2.5 Ah

So, let us assume that for 18 kWh battery,
Total Voltage = 72 Volt.

No. of Cells in series = Total Voltage/Nominal cell Voltage
= 72/3.3
= 21.819 = 21

Now, as we know that battery pack capacity (Wh) = Total current x Total voltage = (2.5 x Cell in parallel) x 72

18000 = (2.5 x cell in parallel) x 72

No. of Cells in parallel = Total current/Cell capacity
= 18000/(2.5 x 72)
= 100

Total No. of cells in battery pack = No. of Cells in series X No. of Cells in parallel
= 21 x 100
= 2100

Overall Output Voltage of Battery Pack = No. of Cells in series X Nominal Voltage of cell
= 21 x 3.3
= 96.3 Volt

Rated Capacity of Battery pack = No. of Cells in parallel X Cell Capacity
= 100/2.5
= 40 Volt

Now I will explain how a Battery Pack is formed and steps included...

Battery Connection:- We connect cells in two ways-
(i) Series connection
(ii) Parallel connection

(i) Series Connection:- Series connection is the connectivity of the components in a sequential array of components. In series, cells are joined end to end so that the same current flows through each cell. In case if the cells are connected in series the emf of the battery is connected to the sum of the emf of the individual cells.

(ii) Parallel Connection:- Parallel connection is the connectivity of the components alongside to other components. In a parallel combination, all the positive terminal are connected together and all the negative terminal are connected together.

Welding connection:- We can weld cells in two ways-
(i) Spot welding Connection
(ii) Laser welding Connection

(i) Spot welding Connection:- A form of resistance welding, spot welding is one of the oldest welding processes whereby two or more sheets of metal are welded together without the use of any filler material. The process involves applying pressure and heat to the weld area using shaped alloy copper electrodes which convey an electrical current through the weld pieces.

(ii) Laser welding Connection:- Laser welding is a good choice for joining battery tabs during battery pack assembly. The process is fast and efficient. It produces high-strength welds for all material combinations.

Holders:-

• Each of the cells are now need to be connected so that it could form a big battery module.
• So this holdes are very importatnt to provide the gapping between the battery and holding the battries in the correct manner.
• The cells has a vent at the end cap of the cell.and should not be covered by any mechinical means.Blocking the cell vent and then sufficiently abusing the cell so as to built the pressure in cell.There must be minimum of 1mm spacing between each cells to allow the vent to open under the fault condition.
• Holders will make it easy to palcethe contact plate between the cells.

Protection Vainting:- These vents help protect automotive battery packs and support battery life and reliability through four key functions:

• Sealing and guarding against water, dirt, contaminants and harsh automotive fluids.
• Continuous pressure equalization to help protect the battery housing against excess over- or under pressure during the life of the battery.
• Effective ventilation, allowing damp air which could accumulate inside the battery housing to be expelled with each warming-up cycle, helping to avoid potential internal condensation issues under certain atmospheric conditions.
• Help ensure proper mitigation in case of a thermal runaway event inside the battery, allowing large amounts of gases to be expelled in a short timeframe.
  

BMS:-

A battery management system (BMS) is any electronic system that manages a lithium battery pack and the main functionalities are

1. Monitors all of the parallel groups in the battery pack and disconnect it from the input power source when fully charged.
2. Balance all the cells voltage equally
3. Doesn't allow the pack from over-discharged.