Project 1 Mechanical design of battery pack
Q.
Battery pack capacity: 18 kWh
Cell: ANR26650M1-B
Prepare a detailed battery pack drawing along with its enclosure. State your assumptions.
A.
Battery Specifications
Nominal voltage - 3.3 V
Nominal capacity - 2.5 Ah
Battery Pack Requirements
Capacity - 18000Wh
- 900Ah*200V
- (2.5Ah *360) * (3.3V* 60)
- 60* [(2.5Ah *6) and (3.3V*1)]
Therefor, 60 battery modules, each with
- 1S6P configuration
- 300Wh capacity
- 6V
Each module
Cells are conncected together by means of Nickel strips or thick wire. Generally, Nickel strips are widely used for this and there are two types available: nickel-plated steel strips and pure nickel strips. Pure nickel is costlier than nickel-plated steel, but it has much lower resistance. Low resistance means, less heat generation during the charging and discharging, which leads to longer useful battery life. Each module contains 6 cells in parallel. Such 60 modules are connceted in series using spot welding with the nickel strips as shown in the figure above.
There are two ways of connecting these in series. Straight packing will give a narrower but long battery, but since there are gaps in between, it’ll be less compact compared to offset packaging.
Stack of 10 1s6p batteries. Six more similar stacks can be connceted in series to get the required capacity of 18kWh. For series connection, the positive of first set is spot welded to the negative of 2nd set. This is continued for all the sets.
The offset battery holders shown above are expandable and can be used to connect 60 1s6p sets.
After that, cells can be put in heat syncs for thermal management. Shown above are aluminium heat syncs that can minimise ruptures, avoid cell contact, arrests flames and protect from abuse. The right hand side figure shows an example of how he modules an be enclosed in a housing with voltage sensors and BMS with a cooling plate at the bottom.
Reference
http://www.diybatteries.com/category/instructions/
https://www.instructables.com/DIY-Professional-18650-Battery-Pack/