Project 1 Mechanical design of battery pack

1. Battery pack capacity: 18 kWh

Cell: ANR26650M1-B

Prepare a detailed battery pack drawing along with its enclosure. State your assumptions.

Solution:

Aim:

Prepare a detailed battery pack drawing along with its enclosure. Of Cell: ANR26650M1-B and State the assumptions.

Objectives:

• Collecting the data’s of Cell: ANR26650M1-B.
• Calculating all Electrical parameters for 18 kWh Battery Pack.
• Calculating all Physical dimensions for Battery Pack.
• Consider perfect enclosure for dimensions that we calculated for the Battery Pack.

Theory:

• The Cell: ANR26650M1-B datas are refferd from the link, https://sklc-projects-2021.s3.amazonaws.com/projects/2021/53263/59106.txt

https://a123batteries.com/anr26650m1-b-lithiumwerks-nanophosphate-3-3v-2-5ah-lithium-iron-phosphate-battery/

ANR26650M1-B Specifications

• Nominal Ratings
  Voltage: 3.3 Volts
  Capacity: 2.5 Ah
  Energy: 8.25 Wh
  Specific Power: 2600 W/kg
  Impedance (1KHz AC Typical) 6 mΩ
  Cycle Life at 1C/1C, 100% DOD: > 4000 cycles
  Cell Type: 26650 Lithium Ion Power Cylindrical Cell
• Discharging
  Max Continuous Discharage: 50 A
  Max Pulse Discharge Current >50% SOC (10s): 120 A
  Minimum Voltage: 2 Volts
  Temperature: -30ºC to 55ºC
• Charging
  Recommended Standard Charge: 2.5 Amps
  Max Charge Rate: 10 Amps
  Max Pulse Charge Current <50% SOC (10s): 25 A
  Float Voltage: 3.45 Volts
  Recommended charge V & Cut-off Current: 3.6 Volts, taper to 125mA
  Temperature
  (reduce charging current to 250mA when under 0ºC): 0ºC to 55ºC
• Mechanical
  Diameter: Ø25.96 +/- 0.5 mm (1.0")
  Length: 65.15 +/- 0.5 mm (2.6")
  Mass: 76 g
• Calculation as per assumptions- 18kWh Battery Pack
• Calculation for designing an 18kWh battery pack, basically 18kWh is energy require to achieve the vehicle its proper range. It is depending upon the voltage (V) parameter and ampere-hour or capacity (Ah).
• Here we design a high voltage battery pack for an electric vehicle to achieve its range up to 220 km. For this calculation, I assumed 145.2 V a nominal voltage for series connection.

Cell calculation:

• Volume of the cell: For the calculation of the volume of the cell we use the formula of Volume of cylinder.

So the formula is: π r² h

From Datasheet of Cell, we have 'r' and 'h' values

R = 0.013m and h = 0.065 m

Volume of the cell: π r² h

= 3.14 * 0.0132 * 0.065

= 0.0000344929 m³

The volume of the cell is 0.0000344929 m³

Basically, the value of the volume of the cell is used to find out the total volume of the battery pack.

• Cell Energy = Cell Capacity (Ah) × Cell Voltage (V)

= 2.5 × 3.3

= 8.25 Wh

Cell Energy is 8.25 Wh

The value of a single cell is used to calculate the total energy of the battery pack.

• Single Cell Energy Density

Volumetric energy (Wh/m³) = Single Cell Energy / Volume of each cell

= 8.25 Wh / 0.0000344929 m³

=2, 39,179.6572 Wh / m³

Single Cell Energy Density is 2, 39, 179. 6572 Wh / m³

• Assume:

Vehicle Range = 250 KM
Battery Pack capacity = 18 kWh or 18000 Wh
Now,
We will calculate per km average energy = 18000/ 250
= 72 Wh/km

Therefore,
Battery Pack total energy = Average energy x km
= 72 x 250
= 18000 Wh or 18.120 kwh

• Battery Pack Assumptions:

There are 50 cell are in series and 44 cells are in parallel, and as above maintained we are going to use Cell: ANR26650M1-B this cells.

• Battery Pack calculation:

Now we calculated parallel and series combinations so we can now calculate total no of cells required

Total no of cells = Series cells * parallel cells

= 50*44

Total no of cells = 2200.

So from series and parallel combination, we can calculate the voltage of battery pack and the current of the battery pack.

Voltage = no of cell in series* nominal voltage.

= 50*3.3

= 165V

The total value of voltage is 165V.

Current = No of parallel cells * cell capacity

= 44*2.5

=110Ah.

The total value of Current is 110Ah

So now we can calculate the how much mount of energy this combination have by product of voltage and current, and check the it will satisfied or not our requirement

Energy= Voltage * Current

= 165 * 110

= 18150WAh

The total value of Energy is 18150WAh.

So our calculation is satisfied requirement what we need.

Now we have total no of cells and volume of single cell so we can calculate the total volume required for battery pack

Total volume = no of cells * Volume of single cell

= 2200 * 0.0000344929

=0.07588438 m³

Total volume required for battery pack is 0.07588438m3m3

We also have single cell weight from that we can calculate the total weight of battery pack without other mechanical and electrical connections.

Weight = No of cells * weight of single cell.

= 2200 * 0.076

= 167.2kg

Weight of battery pack is 167.2kg

Energy density = volume * battery pack energy

= 0.07588438 * 18150

= 1, 377. 301497 kWh/m³

Energy density is 1, 377. 301497 kWh/m³

Now we all parameters which we need to construct the battery pack in physically.

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 together into a single mechanical and 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 and 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] and 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 and providing the spacing between the batteries.

2) Connecting the batteries with the strips (Series or Parallel)

3) Making and manufacturing the battery enclosure housing with the thermal management system and BMS

1) 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.

2) 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 building.
• Its due to its efficiency of usage in spot welding and soldering as well its high corrosion resistance over time.
• It has good properties and excellent resistance to many corrosive environments.
• The pure nickel will never get rust after it applied to battery packs.
• It won’t affect the current transfer between batteries.Pure nickel strips are the material you want, but many vendors swap out it for nickel-plated steel strips, which are poorer and have greater resistance – not suitable for most battery projects. 100% pure nickel strip.
• verify all of our strips to assure that you are getting the high-quality pure nickel. It also solder 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 managment of battery and BMS

• The battery encolsure is the final protection of the battery.
• So the battery enclose must be very strong and light in weight.
• In the case of any accident the batteries has the tendentcy of catch fire if it get leaked during the car crash,so the battery modle is enclose in a very strong encolsure due to the safety.
• The weight should be less so we can get the best pssible range.
• In this metal housing there is a temperature managment system provided to cool and heat the battries when there is a need to get the best performace of the battries.

There a several numbers of models connected in series and parallel to build a entire battry pack.

TESLA 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 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

Conclusion:

Thus we have studied how to model a battery pack for 18kw battery.

NO	Calculated Parameters	Value Get
1	Cell Volume	0.0000344929 m^2
2	Cell Energy	8.25Wh
3	Cell Density	239179.6572kWh/m^2
4	Pack assumptions	50s 44p
5	Total no of cells	2200
6	Voltage	165V
7	Capacity	110Ah
8	Energy	18150WAh
9	Total volume	0.07588m^2
10	Total Density	1377.30kWh/m^2
11	Weight	167.2kg