Project 1 Mechanical design of battery pack

Objective: Battery pack drawing along with its enclosure. 

Given: 

• Cell: ANR26650M1-B
• Battery pack capacity: 18 kWh

ANR26650M1-B: 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.

Nomenclature of Battery:

where; R-cylinder, 26*65 mm where 25 is diameter and 65 is height as shown below:

From Datasheet:

Battery pack is a set of any number of identical batteries or individual battery cells. They may be configured in a series, parallel or a mixture of both to deliver the desired voltage, capacity, or power density.

To create battery pack of 18 KWh:

• As, Cell Voltage is 3.3V and Cell Capacity is 2.5Ah.
• So, Single cell is of 8.25Wh (P=V*I).
• No of cells required for 18KWh battery pack is 2182 (18000/8.25 =2181.8).
• So, Possible combinations of battery packs with 2184 cells are: 52s42p and 42s52p.
• Lets take example of 42s52p where 42 cells are in series in 52 legs or branches.

 

• Current in series remain same and voltage in parallel remain same.
• parallel legs=52
• Each parallel leg has 42 cells in series.
• so, 1 parallel leg has 42 cells and 1 cell has 3.3V; Overall voltage will be 138.6V (42*3.3)
• 1 cell current is 2.5Ah and current in 1 parallel leg is also 2.5Ah; Overall current in 52 parallel legs will be 130Ah (52*2.5)
• Overall capacity of battery pack will be 18023.2 Wh (138.6*130)
• So, Here we are designing the battery pack with capacity of 18.0232 KWh.

Cell to Module to Battery Pack: 

• Configuration of cells into larger modules that includes some electronic management.
• Installation of modules together with systems that manage power, charging and temperature.

Battery Module:

• In configuration of  42s52p, assumed the battery module of 4s7p, where 4 cells are in series in all 7 parallel legs.
• So each module has 28 cells (4*7).
• Battery modules required for 42s52p are 78. (Total no of cells/No of cells in module=2184/28)

• 13 modules (in parallel) * 6 modules (in series)=78 Modules
• 2184 (Total Cells) = 28 (cells/module) * 78 (modules )

Parts used in Battery Pack:

Interface	Definitions	Parts
Mechanical	Mechanical design features included for safety reasons	Cell spacers, Damping pads, gaskets, valves
Structural	Members that provide required protection and isolation	Case, Cover, end-plates, tie-rods, cross members
Thermal	Regulates battery temperature	Coolant, fans, pumps, heat exchangers
Electrical	Transmits power from and to the battery pack	Bus-bars, Cables, Contactors, Fuse, Relay
Control	Monitor and regulate the state of battery pack	Battery Management system, Various sensors
Support	Vehicle body parts providing additional crash worthiness	Axles, chassis, seats, vehicle floor

Mechanical:

• 4x7 Cell Spacers

• Damping Pads

Structural and electrical:

• Electrical connections are done by using connectors or by soldering.
• Connectors can be made up of aluminium, copper, SIGMAclad.

SIGMAclad

• Lego connectors are also used.

Thermal and Control:

• Heating and cooling plate

 Steps to design battery pack:

• Use cell spacers for lithium ion cells.

• Nickel metal strips are used with spot welding.

• BMS(Battery Management system) is connected with battery as shown below:

 

• Isolation of each module:

• Cooling with Fan and Casing/Enclosure of battery Pack.

Overall Battery Pack:

• It consist of 78 battery modules and each module has 28 cells. So, entire battery pack has 2184 cells. 
• Connections are done by using nickel strips with spot welding.
• Have Battery Management system(BMS)
• For cooling, Fan and plates are used.

 

PARAMETERS	SINGLE CELL
Voltage in V	3.3
Capacity in Ah	2.5
Diameter in mm	26
Height in mm	65
Weight in g	76

1 Module Configuration: 4s7p
No of cells	28
Voltage in V	13.2
Capacity in Ah	17.5
Width in mm	104
Length in mm	182
Height in mm	65
Weight in kg	2.128

Whole Battery Pack Configuration: 42s52p
No of cells	2184
Voltage in V	138.6
Capacity in Ah	130
Width in mm	1092
Length in mm	1352
Height in mm	65
Weight in kg	165.984

•  By adding BMS, Cooling System, Connectors, Cell spacers, etc. Weight will increase and dimensions will also change.