Project 1 Mechanical design of battery pack
Mechanical design of a Battery pack
Aim :
To configure the Mechanical design of Battery pack for 18 kWh energy with the Lithium-ion cells and state our assumptions.
Theory :
ANR26650M1-B cell :
This LiFePO4 battery is a A123's high-performance Nanophosphate lithium iron phosphate (LiFePO4) battery technology delivers high power and energy density combined with excellent safety performance and extensive life cycling in a lighter weight, more compact package. The cells have low capacity loss and impedance growth over time as well as high usable energy over a wide state of charge (SOC) range, allowing our systems to meet end-of-life power and energy requirements with minimal pack oversizing.This versatile lithium ion cell is suitable for a wide variety of applications and system designs. Proven performance in the toughest conditions, combining durability, reliability and safety.
Cylidrical Cell primary Applications :
- Portable high power devices
- Stationary battery backup systems
- Grid stabilisation energy storage system
- Commercial truck and bus hybrid electric vehicles (HEVs)
Nanophosphate LiFePO4 Benifits :
- Cycle Life 1C/1C, 100% DoD,> 4000 cycles
- Safety:Excellent abuse tolerance and environmentally friendly
- Life: Excellent calender life, 10X cycle life vs. conventional lithium ion
Data sheet :
The datasheet for this LiFePO4 is downloaded from the internet as the PDF file from that the battery dimesions, voltage, capacity, temperature, charging and discharging charecteristics are present in the datasheet. And we going to make the battery pack for the required 18kWh by this cell for that this datasheet will used for the calculations.
Specifications :
Dimensions :
Discharge charecteristic with Temperature :
Discharge charecteristic with C-rate :
Life cycles :
Calculations for 18 kWh Battery :
single cell enegy :
Cell voltage = 3.3 V
Capacity = 2.5 Ah
Energy = voltage x capacity
= 3.3 x 2.5
single cell enegy = 8.25 Wh
The value of a single cell is used to calculate the total energy of the battery pack.
Energy Density :
Here,
weight of the cell = 76 grams (or) 0.076 kg
Gravimetric energy (Wh/kg) = Single cell Energy / weight of the cell
= 8.25 / 0.076
Energy Density = 108.55 Wh/kg
As we know the Required energy is arround 18kWh and the formula is as following
Required Energy = pack voltage x pack current
18000 = pack voltage x pack current
calculation for pack voltage,
here we going to assume the required voltage for the battery pack as arround 140V to 150V
So, if pack Voltage = 140V means
then,
pack voltage = No. of series connection x single cell voltage
140 = No. of series x 3.3
No.of series = 140 / 3.3
No. of series = 42.42 ~ 43
if pack Voltage = 150V means
then,
pack voltage = No. of series connection x single cell voltage
150 = No. of series x 3.3
No. of series = 150 / 3.3
No. of series = 45.45 ~ 45
from the above calculation the for 140V and 150V we have find the no.of series connections is 43 and 45. so, from this we have select the 44 series connection for this Battery model.
so,
No.of series connection = 44 cells
pack voltage :
pack voltage = No.of series x single cell voltage
= 44 x 3.3
pack voltage = 145.2 volts
calculation for pack current,
Required Energy = pack voltage x pack current
18000 = 145.2 x pack current
pack current = 18000 / 145.2
pack current = 123.97 Ah
So,now find No.of parralel connections
pack current = No.of parralel connections x single cell current
123.97 = No.of parralel connections x 2.5
No.of parralel connections = 123.97 / 2.5
= 49.59 ~ 50
No.of parralel connections = 50 cells
pack current :
pack current = No.of parallel x single cell current
= 50 x 2.5
pack current = 125 A
Battery Pack enegy :
Pack voltage = 145.2 V (44 series)
Pack Current = 125 Ah (50 parallel)
Pack Energy = Pack voltage x Pack capacity
= 145.2 x 125
Battery Pack enegy = 18150 Wh (or) 18.15 kWh (Required)
Required total cells :
Total cells = No.of series x No. of parallel
= 44 x 50
Total cells = 2200 cells (Required)
Cell peak current :
Cell peak current = C-rate * single cell current
= 20 x 2.5
Cell peak current = 50 Amps
Battery peak current :
battery peak current = cell peak current x No.of parallel
= 50 x 50
Battery peak current = 2500 A
Battery peak power :
peak power = peak current x pack voltage
= 2500 x 145.2
= 363000 Wh
Battery peak power = 363 kWh
Mass of the Battery :
Here,
weight of the cell = 76 grams (or) 0.076 kg
Mass of the Battery = Single cell weight x No.of the cell
= 0.076 x 2200
Mass of the Battery = 167.2 kg
Nickel strips :
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 corresive environment. 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.
Battery encloser :
For this battery encloser we select the aluminum as the encloser material. this is up to 50 percentage lighter than an equivalent steel design. Best in class mass energy density at more than 160 wh/kg an extremely efficient design for OEMs and tier 1 Battery pack manufacutures.
Accommodates all battery cell type and is designed particularly for battery electric vehicles with larger power packs such as pick-up trucks sport utillity vehicles and crossovers. most cost-effecitive aluminum solution for mass production electric vehicles when compared to aluminum extrusion and casting intense designs.
Conclusion :
Hence the Mechanical design of Battery pack for 18 kWh energy is designed by the series-parallel connection. 44 cells are in series connection and 50 cells are in parallel connection and produce the 18.15 kWh and peak power of 363 kWh with the Lithium-ion cells. And the overall mass of the Battery is 167.2 kg.
Reference :