Project 1 Mechanical design of battery pack
Battery pack capacity: 18 kWh
Cell: ANR26650M1-B
Prepare a detailed battery pack drawing along with its enclosure. State your assumptions.
Computing the cell parameters:
This calculation is to determine the capacity space required for a cell to have a capacity of 18 kW.
Cell energy = nominal voltage x nominal cell capacity
Cell energy=3.3*2.5
= 8.25 watts
The energy of each cell is 8.25 watt hours.
Cell volume = pi *r*r*h
=3.14*0.013*0.13*0.065
=0.0344929 m^3
Therefore, we need to calculate the watts per volume that the cell can produce.
Cell energy density = cell energy/cell volume
=8.25/0.0344929 Wh/m^3
=239.17Wh/m^3
Now we have to assume the battery pack.
To obtain an output power of 18 kW, we need to consider series and parallel cells to create a battery pack module with the required capacity.
Consider 58 cells in series and 38 cells in parallel.
So total number of cells required = 58 * 38 = 2204 cells
Closed voltage = nominal voltage * cells connected in series
=3.3*58
=191.4 V
Current capacity of battery pack = cell capacity x number of cells connected in parallel
=38*2.5
= 95 Ah
Total energy of the battery pack = voltage x current capacity
191.4*95
= 18.18 kW
Now that we know the total number of cells required for the battery pack, we can calculate the energy density and total weight of the battery pack.
Total volume = cell volume * total number of cells
0.0344929*2204
=76.022m^3
And Total battery weight = total number of cells * weight of each cell
2204 x 0.076 kg
The total weight of the battery is 167.504 kg. Now that we know the weight and volume of the 18kW battery pack, let's build the battery pack.
Battery pack:
A battery consists of one or more electrochemical cells (battery cells) that convert chemical energy into electrical energy (during discharge) and electrical energy into chemical energy (during charging).
The types of elements in the battery and the chemical reactions during the discharge/charge event define the battery cell chemistry. Battery cell chemistry consists of five main components: electrodes - anode and cathode, separator, terminals, electrolyte, and case.
Individual battery cells are grouped into a mechanical and electrical unit called a battery module.
3 Types of battery Pack Design:
- Cylinderical>> Hard Case
- Prismatic >> Hard case >> Pouch
Battery Pack construction:
There are 3 steps for the construction of the battery pack.
1)Battery holding and providing the spacing between the battries.
2)Connecting the battries with the strips (Series or Parallel)
3)making and manifacturing the battery enclosure housing with the thermal managment system and BMS.
Holding and Spacing:
- 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.
Single cell Holding and Spacing 
Connecting the cells:
- When the cells are plalced in the holders ,then the cells need to be connect in the proper manner in series or parallel to get the desired results.
- Ususally a nickle strip is used between the cells to make the conatct.
- Nickel strip is generally used in battery manufacturing.
- This is due to the efficiency of use in spot welding and soldering, as well as high resistance to corrosion over time.
- It has good properties and excellent resistance to many corrosive environments.
- Pure nickel never rusts when applied to batteries.
- It will not affect the current transfer between the batteries. Pure nickel tape is the material you want, but many dealers swap it out for nickel-plated steel tape, which is leaner and more durable - unsuitable for most battery projects. Band made of 100% pure nickel.
- verify all our strips to ensure you are getting high quality pure nickel. They also solder incredibly fast, so you can weld them onto your existing busbars to increase the supply of current you can pull through the busbars. The benefits are almost limitless.
3) Battery cover and battery thermal management and BMS
- The battery cover is the ultimate battery protection.
- So the battery cover has to be very strong and light.
- In case of any accident, batteries tend to catch fire if they leak in a car accident, so the battery module is enclosed in a very strong case for safety.
- The weight should be lower to get the best possible range.
- This metal case houses a temperature management system to cool and heat the batteries when the best performance of the batteries is needed.
- There are several models connected in series and in parallel to form a complete set of batteries.
BMS stands for Battery Management System, which is an electronic system that monitors and controls the performance of rechargeable batteries, including lithium-ion batteries, in various applications. The primary function of a BMS is to ensure that the battery operates within safe operating limits and is protected from damage or failure due to overcharging, undercharging, overheating, or over-discharging.
There are different types of BMS available in the market, depending on the application and battery type. Some of the common types of BMS are:
1. Centralized BMS: In this type of BMS, all battery cells are connected to a central control unit that monitors and manages the performance of the battery pack.
2. Distributed BMS: In a distributed BMS, each battery cell has its own control unit that communicates with other units in the pack to coordinate the operation of the battery pack.
3. Modular BMS: This type of BMS is designed for large battery packs where each module has its own BMS unit that can be connected to other modules in a series or parallel configuration.
4. Passive BMS: In a passive BMS, the system uses passive balancing circuits to equalize the voltage of each battery cell in the pack.
5. Active BMS: An active BMS uses active balancing circuits that can transfer charge from high voltage cells to low voltage cells in the pack, ensuring that all cells are balanced and the battery operates at maximum efficiency.
Coulomb counting is a method used by BMS to estimate the state of charge (SOC) of the battery pack. It works by measuring the amount of current flowing in and out of the battery over time and then integrating the current measurement to calculate the total charge transferred. The SOC of the battery pack is then estimated based on the remaining charge in the battery and its nominal capacity. By implementing coulomb counting, the BMS can accurately estimate the SOC of the battery pack and ensure that the battery operates within safe limits.
Conclusion:
Thus we have studied how to model a battery pack for 18kw battery with relevent figures and Formulae to calculate the cell parameters.