Project 1 Mechanical design of battery pack
Battery pack capacity: 18 kWh
Cell: ANR26650M1-B
Prepare a detailed battery pack drawing along with its enclosure. State your assumptions.
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. Our 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.
Overview: Cell, Battery & Battery Pack:-
A Cell refers to a single anode and cathode seperated by electrolyte used to produce a voltage and current. A battery can be made up of one or more cells. Example - A single AA Battery is one Cell.
Battery :- A battery is a source of electric power consisting of one or more electrochemical cells with external connections for powering electrical devices such as flashlights, mobile phones, and electric cars.
Battery Pack:- A 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.
Energy:- 18KWh
Number of cells(N) = Energy/(Nominal Voltage * Capacity)
N = 18000/(3.3*2.5) = 2182
We need 2182 cells to get 18kWh energy, We can now decide the configuration in series and parallel.
In Series configuration the Capacity remains the same and voltage will be sum of the individual cell voltage.
In Parallel configuration The voltage remains the same and the capacity accumulates.
Ex:- Let's say uf wee need 330V to run a vehicle.
The nominal voltage of one cell is 3.3V.
Number of cells required to be connected in series connection to produce 330V(Ns) = Voltage required / Nominal voltage of one cell
Ns = 330/3.3 =100. Therefore 100 cells connetected in series will generate 330Voltage and the capacity of the whole module will be 2.5Ah.
Now we need to find the number of cells which will be connected in parallel configuration (Np)
Np = Total cells /No of cells in series (Ns)
Several cells can't be infracted so we take 22 cells for each parallel row, although it is exceeding the required capacity that is negligible.
Cell architechture = 100 series and 22 parallel i.e 100S22P
Battery Capacity:- We know parallel configured cell multiplies individual cell capacity so
Capacity = Parallel cell row * Individual Cell Capacity
Capacity = 2.2*22 = 55.0 Ah
Current Supplied by Battery
We have already calcualted battery capacity which is 55 Ah means it is going to supply 55A current per hour. Which can be considered a C-rate.
Range:- Powertrain Energy Consumption = 129Wh/Km at 70% powertrain efficiency
Range Capacity = Capacity/Energy consumed per kilometer.
Range = 18000/129
Range = 139Km.
The vehicle will be able to cover 139km with above parameters.
Internal Resistance of a battery :-
The entire resistance encountered by a current as if it flows through a battery from Negative to the Positive terminal Known a s internal resistance of a bettery.
Battery Dimension:-
ANR26650 cell has 26mm diameter and 65 mm height. We need to decide battery size and Casing size.
Length of the Casing(L) = number of cells at mid*Cell diameter (26)+Margin at both sides of the cell(4)+clearance at side (Diameter of edged cell + Margin)
L = 98*30+60 = 3000mm
Breadth of Casing(B) = Cell Diameter (26)+ Margin at both sides of cell(4)+Clearance at side (Diameter of edged cell +margin)
B = 20*30+60 = 660mm
Height of casing(H) = 65+36 (height of cell + Margin for Wiring, Cell holders and metal strips)
H = 65 +35 = 100mm
Weight of Battery Pack:-
Cell Weight = 76g
Number of cells =2182
Battery Pack weight(W) = Cell weight *number of cells +weight of accessories
W = 76*2182 +4.5 = 165.8 +4.5 = 170.3kg
Battery Pack Assembly:-
Series/Parallel batteries - Battery cells can be connected in series, Parallel and as well as both Series and parallel.
Series batteries: When in a battery Positive terminal of one cell is connected with the negative terminal of succeeding cell the the cells are said to be a series connected or Simply Series battery. Here overall emf of a battery is algebric sum of all individual cells connected in series, But overall discharges current of a battery does not exceed the discharge current of individual cells.
Parallel batteries:- When a positive terminals of all cells connected together and similarly negative terminal of these cells are connected together in a battery then the cells are said to be connected in parallel. These combinations are also referred as Parallel Batteries. If emf of each cell is identical then the emf of the battery combined by the number of cells connected in parallel is equal to the emf of each cell. The resultant internal resistance of the combination is
Parallel Connected Battery Cells
Mixed Grouping of Batteries or Series Parallel Batteries:
The Cells in a battery can also be connected in mixture of both series and parallel. These combination are some time referred as series parallel battery. A load can require both voltage and current more than that of an individual battery cell. For achieving the required load voltage, The desired number of battery cells can be combined in series and for achieving the required load current the number of cells connected in parallel.
Components required to Assemble Battery Pack:-
Required - 2200 cells, Nickel Strips, PVC Heat Sink film, Spot welder, Connectors, Cell Holders and Solder.
We are goining to start with snapping square cell holders togeteher. One can use cell terminal blocks, but they will consume more space than hexagonal holder. Put insulator gasket on Positive side of cell,
Placing cell in Cell Holder Ex:-
Connecting the Battery with Nickel Strip. Ex:-
After making Connections, Stick PVC Heat sink Film to cells. Solder balancing wire to terminal and battery management system current supply wire to battery pack.
Connect balancing wire pin to the BMS and Glue it to the side of battery Pack with BMS,
Assemble the Battery pack with enclose made up of Plastic or metal or plastic sheets.
Exploded view of a Battery pack.
The images used above is just the representation for showing the steps Actual battery pack will be made as per the calculations that we have considered for cell - ANR26650M1-B.