Project 1 Mechanical design of battery pack

AIM: Prepare a detailed battery pack of Cell: ANR26650M1-B, drawing along with its enclosure, & Battery pack capacity is 18kWh. State your assumptions.

Abstract:-

• In this project, we will calculate all the parameters required the build an EV battery pack.
• We are going to use Cell: ANR26650M1-B for our battery pack. In parameters, we will consider all electrical aspects like temperature, Depth of discharge, Operation current, Energy density, Work cycles, Battery capacity, State of Charge (SOC), State of Health (SOH), and Ampere-hour (Ah) Capacity.
• We also calculate all geometrical considerations like size, weight, volume, area, etc. In the end, we consider some enclosure models for our battery pack.

Theory:-

Battery pack architecture:

All high-voltage battery packs are made up of battery cells arranged in strings and modules., A battery cell can be regarded as the smallest division of the voltage.

Individual battery cells may be grouped in parallel or in 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 it is determined by the number of cells in a series. For example, the total (string)voltage of 6 cells connected in series will be the sum of their voltage.

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.

An example is the high voltage battery pack of the Tesla Model S, which has:-

• 74 cells in a parallel-group
• 6 groups in series for a module
• 16 modules in series
• 7104 cells in total

Battery pack production line:

PROCEDURE:-

1. First, we have to start with Cell calculation.
2. Then, we will make Battery Pack assumptions.
3. After assumptions, we have to do Battery pack calculations.
4. From Cell Dimensions, we calculate the surface required for a battery pack.
5. Depending upon the above calculations, we build Battery Pack construction.

Dimension of the cells:

Calculation :

This calculation determines how much space the cell will take in to have the capacity of 18kw.

Cell energy=Nominal voltage X nominal cell capacity

Cell energy=3.3X2.5

=8.25Wh

sor each cell has an energy of 8.25 wh.

Cell Volume=π*r*r*h

=3.14x0.013x0.13x0.065

=0.0344929 m^3

So now we have to calculate how many watts per volume the cell can produce:

Cell energy density =cell energy/cell volume

=8.25/0.0344929 Wh/m^3

=239.17 wh/m^3

Now we have to assume the battery pack:

To get 18 kW as an output power, we have to consider series and parallel cells to be connected to create the battery pack module of the required capacity.

Let us consider 58 cells connected in series a and 38 in parallel.

So the total number of cells required =58X38=2204 cells

The voltage of the pack =Nominal voltage X cell connected in series

=3.3x58

=191.4

The current capacity of the battery pack=Cell capacity X Cells conned in parallel

=38x2.5

=95Ah

The total energy of the battery pack =Volatage X current capacity

191.4x95

=18.18KW

Now we know the total number of cells that are required in the battery pack, we can now calculate the energy density, volume and weight of the entire battery pack.

Total volume =Cell volume X Total no of cells

0.0344929x2204

=76.022m^3

And

Total weight of the battery=Total no of cells X Weight of each cell

2204x0.076 kg

=167.504 Kg is the total weight of the battery

Now we know the weight and volume of the battery pack of 18kw.So, we will construct the battery pack.

Battery Pack:-

• A battery consists of one or more electrochemical cells (battery cells) which are converting chemical energy into electrical energy (during discharging) and electrical energy into chemical energy (during charging).
• The type of elements contained within a battery and the chemical reactions during discharging-charging events define the chemistry of a battery. A battery cell consists of five major components: electrodes – anode and cathode, separators, terminals, electrolyte and a case or enclosure
• Individual battery cells are grouped into a single mechanical & electrical unit called a battery module.
• The modules are electrically connected to form a battery pack.
• There are several types of batteries(chemistry) used in hybrid & electric vehicle propulsion systems but we are going to consider only Lithium-ion cells. The main reason is that Li-ion batteries have higher specific energy [Wh/kg] & specific power [W/kg] compared with other types.

Ev uses mainly 3 types of cells:Cylindrical,prismatic and pouch.

Battery Pack construction:

There are 3 steps for the construction of the battery pack.

1) Battery holding & providing the spacing between the batteries.

2) Connect the batteries with the strips (Series or Parallel).

3) making & manufacturing the battery enclosure housing with the thermal managment system and BMS.

1)Holding and spacing:

• Each cell now needs to be connected to form a big battery module.
• So, these holders are very important to provide the gap between the battery and correctly holding the batteries.
• The cells have a vent at the end cap of the cell.& should not be covered by any mechanical means. Blocking the cell vent and then sufficiently abusing the cell to build pressure in the cell. There must be a minimum of 1mm spacing between each cell to allow the vent to open under the fault condition.
• Holders will make placing the contact plate b/w the cells easy.

2) Connecting the cells:

• When the cells are placed in the holders, then the cells need to be connected properly in series or parallel to get the desired results.
• Usually, a nickel strip is used between the cells to make the contact.

• Nickel strip is generally used in battery building.
• It's due to its efficiency of usage in spot welding and soldering and its high corrosion resistance over time.
• It has good properties & excellent resistance to many corrosive environments.
• The pure nickel will never get rust after it is applied to battery packs.
• It will not affect the current transfer between batteries. Pure nickel strips are the material you want, but many vendors swap out for nickel-plated steel strips, which are poorer and have greater resistance – unsuitable for most battery projects. 100% pure nickel strip.
• verify all of our strips to ensure you get a high-quality pure nickel. It also solders incredibly quickly, so you can weld them onto your existing busbar connections to raise the supply of current you can pull through the busbars. The benefits are nearly limitless,

3)Battery enclosure and thermal management of battery and BMS-

• The battery enclosure is the final protection of the battery.
• So, the battery enclosure must be very strong and light in weight.
• In the case of any accident, the batteries tend to catch fire if they get leaked during the car crash, so the battery module is enclosed in a very strong enclosure due to safety.
• The weight should be less so we can get the best possible range.
• In this metal housing, a temperature management system is provided to cool and heat the batteries when there is a need to get the best performance.
• There are several numbers of models connected in series and parallel- to build an entire battery pack.

BMS:-

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

1. Monitors all of the parallel groups in the battery pack & disconnects it from the input power source when fully charged

2. Balance all the cell's voltage equally.

3. Doesn't allow the pack from over-discharged.

Conclusion:-

1. Thus, I have studied how to model a battery pack with an 18KW capacity.
2. Lithium Ion and Lithium Ion Polymer batteries are great power sources for some applications but require preventive protection during discharging and charging.