Challenge

Project 1 Mechanical design of battery pack

TTom Thankachan24 Jul 2022

Battery pack capacity: 18 kWh

Cell: ANR26650M1-B

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

Nanophosphate High Power Lithium Ion C ell ANR26650M1-B A123’s high-performa nce Nanophosphate lithium iron phosph ate (LiFePO4) battery technology delive rs high power and energy density combin ed with excellent safety performance an d extensive life cycling in a lighter weight, more compact package.

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Based on the Lithium iron phosphate chemistry(LiFePO4),the cells are inherently safe over a wide range of temperature and conditions.

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APPLICATIONS

GRID SOLUTIONS
+ Frequency regulation
+ Renewables integration
+ Reserve capacity
+ Transmission and distribution

TRANSPORTATION SOLUTIONS
Hybrid, plug-in hybrid and electric vehicle battery systems for:
+Commercial vehicles
+ Off-highway vehicles
+Passenger vehicles

COMMERCIAL SOLUTIONS
Advanced lead acid replacement batteries for:
+ Datacenter UPS
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GOVERNMENT SOLUTIONS
+ Military vehicles
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Constant Power Discharge Characteristics at 23°C.

2.5C Constant Current Discharge at Various Temperatures

Cycle Life Performance, 100% DOD, Various Temperatures and Discharge Rates

The LithiumWerks ANR26650M1-B is the next generation of A123 Systems' pioneering 26650 cylindrical cell, now with greater power and energy density and lower impedance. This versatile lithium ion cell is suitable for a wide variety of applications and system designs.

Assuming that overall voltage required to operate the motor and other acessories of electric vehicle as 400V.

So we have construct the battery pack of 18KWh for a 400 V input voltage motor.

(i) Energy = 18 kWh

(ii) Number of cells (N) = energy / (nominal voltage*capacity)

N = 18000 / (3.3*2.5)

N = 2182

We need a minimum of 2182 cells to get 18 kWh energy, now based on that, we need to decide configuration – series and parallel.

In series configuration capacity remains the same and voltage will be the sum of individual cell voltage.

In a parallel configuration, the voltage remains the same and capacity accumulates.

And we assumed 400 Volts are need to run the vehicle.

The nominal voltage of one cell is 3.3 V

Number of series cells required to produce 400 V (Ns) = voltage required / nominal voltage of one cell

Ns = 400 / 3.3

Ns = 122

122 cells are connected in series will generate 400 voltage and the capacity of the whole module will be 2.5 Ah

Now we need to find the number of cells which will be connected in a parallel configuration

Np (cell in parallel) = total cell / Ns

Np = 2182 / 122

Np = 18

Hence we take 18 cells for each parallel row, although it is exceeding the required capacity, that is negligible.

Cell architecture = 122 Series and 18 Parallel = 122S18P

Battery capacity:

We know parallel configured cell multiplies individual cell capacity so,

Capacity = parallel cell row*individual cell capacity

Capacity = 18 * 2.5

Capacity = 45 Ah

Current supplied by the battery

We have already calculated battery capacity which is 45 Ah means it is going to supply 45 A current per hour. which can be considered as C-rate.

Range:

Let’s powertrain energy consumption = 100 Wh/km at 70% powertrain efficiency

Range = Capacity / energy consumed per kilometre

Range = 18000 / 100

Range = 180 km

So,our vehicle will be able to cover around 180 km with current parameters.

Internal Resistance of Battery:

The entire resistance encountered by a current as if it flows through a battery from the negative terminal to the positive terminal is known as internal resistance of battery.

Battery Dimensions:

ANR26650 cell has 26mm diameter and 65mm height. On the basis of that we need to decide battery size of battery casing.

Length of casing (L) = number of cells at series*(cell diameter (26) + margin at both side of cell (4)) + clearance at side (diameter of edged cell + margin)

L = 122*30 + 60

L = 3720 mm

Breadth of casing (B) = number of cells at parallel*(cell diameter (26) + margin at both side of cell (4) + clearance at side (diameter of edged cell + margin)

B = 18*30 + 60

B = 600 mm

Height of casing (H) = 65+35 (Height of cell + margin for wiring ,Cell holders and metal strips)

H = 100 mm

Weight of battery pack

Cell weight = 76g

Number of the cells = 2182

Battery pack weight (W) = cell weight*number of cells + weight of accessories

W = 76*2182 + 4.5 = 165.8 + 4.5 = 170.3 kg