Project 1 Mechanical design of battery pack

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

Cell:ANR26650m1-B

From the graph the cell specification are

nominal voltage:3.3V with cell capacity:2.5Ah

now based on that, we need to decide configuration – series and parallel but it not exact cells.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

we assumed 330 Volts are need to run the vehicle.The capacity of the total battery for 18kWh is,

Capacity = 18000/330

Battery capacity = 55 Ah

The nominal voltage of one cell is 3.3V & Number of series cells required to produce 330 V (Ns) = voltage required / nominal voltage of one cell

Ns = 330/3.3

Ns = 100 cells in series

The capacity of the whole module will be 2.5 To find the number of cells which will be connected in a parallel configuration

Np = 55/ 2.5

Np = 22 cells in parallel

Here we use 22 cells are in parallel to run the battery with 55 Ah capacity.

The total cell model is having the pack of 100S22P configuration but

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

N = 18000 / (3.3*2.5)

N = 2182 cells here nearly we have 100S22P config.

total no.of cell will be 2200cells with 18.15KWH

Battery module:

The total battery power = (100*3.3 V) * (22*2.5 Ah)

= 18150 Wh i.e = 18.15 kWh

Total number of cells=2200cells

we are dividing the set of cells from battery pack 100s22p into 10s5p

so each module will 50cells,& total no of modules will be 2200/50=44modules

Battery enclosure pack size:

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

Length of casing (L) = number of cells at series*(cell diameter (26) + margin at both side of the cell which to free up space called holders and gaps for the sheet protectors etc (4) + clearance at side (diameter of edged cell + margin) (All should be in value with mm)

L = 100*30+80

L=3080mm

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

B = 22*30 + 80

B=740mm

There fore the total area of the battery is=3080*740mm

=22,79,200mm i.e 2.279M^2

Height of the battery (H) = 65 (height of the cell) + 35 (wires, holders, strips etc) = 100 mm

Therefore, the volume of the battery is = L*B*H

=3080*740*100 i.e =0.228M^3

Weight of battery pack

Cell weight = 76g from data sheet & Total number of cells=2200cells

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

W=76g*2200+500g

W=167.7kg

hence we got the battery sizes its weight, no of cells and modules, pack size with its accessories like wires etc

Materials and process in battery pack construction:

Battery pack constructions consist of three major levels of processings namely cell level,module level,pack level constructions.

The electrodes are combined with electrolyte to various cell models as cylindrical,prismatic,pouch type cells.

After case sealing cells are combained to form module level construction.Finally these modules are combained to form pack level constructions.

Joining technologies of cells:

The interconnections between cells/modules are practised by various welding techniques.Some of them are,

• Ultrasonic metal welding.
• Resistance welding.
• Laser beam welding.
• Wire bonding.
• Mechanical Jooining.

Ultrasonic metal welding-

Ultrasonic metal welding or UMW, is a solid-state welding technique which forms a bond by applying moderate static pressure and an ultrasonic oscillation of about 20 kHz between two

parts of metal. The solid-state weld is formed through the high frequencymotion between the parts causing continuous shearing and plastic deformation, while also removing any oxide layers

or contaminants.

Most metals can be ultrasonically welded and the method is excellent for welding together thin foils, as well as thicker sheets with spot or seam welds and also wires.

The four types of materials welded in this process can be seen as,

a)Aluminium wire welding on copper.

b)Copper and aluminium welding.

c)Multilayered copper foil welding.

d)Ultrasonic seam welding.

Resistance spot welding-

One of the oldest welding methods is resistance spot welding (RSW).RSW is a technique where two or more metal sheets are welded together through the application of an electrical current

and pressure between two electrodes. The electrical resistance of the material at the interface results in the generation of heat and melts the materials together without the use of

filler material or gases.

The temperature increases in the affected area, the interface, and eventually reaches the material’s melting point. A weld nugget forms in the affected area after cooling.

This is a small volume of the material which has melted and then fused together.

Laser beam welding-

Laser beam welding or LBW is a welding technique in which a laser beam provides a concentrated heat source that fuses the materials together.

LBW is commonly performed using keyhole mode welding in which the extreme power density of the laser beam causes the metal to melt and evaporate.

As the metal atoms evaporate from the surface, forces in the opposite direction of the evaporation causes a local vapor pressure. The vapor pressure creates a hole which is known as the

keyhole by depressing the molten metal.

Here below shown the welding of busbars to cylindrical battry cans.

Enclosures:

Cells in series connection-

When you connect cells together in series, it doesn’t change the amps or the capacity, it only raises the voltage of the pack. Hooking them up in series means that you connect the positive end

of one cell (or P-group) to the negative end of the other as shown below.

Cells in Parallel connections-

If you take several cells and connect their same-type electrodes in parallel, they all will act as though they are one large cell. Also, when you first connect them to each other,

they must be at the same level of charge.

Cell holders-

These holders are used for holding the individual cells in a better posture without mis-assemble.The connections can be made accordingly to make series connections and

parallel connections to form the required module dimensions.

After installind the cells in a individual module the entire maximum positive terminal and maximum negative terninal are made under single pair of

terminals as shown below.

Here shown the cells are arranged and welded without using cell holders as,

They are just covered by polimer sheet after the interconnections are made. Mostly connections with cell holders should be recommanded for better

safety concerns.

Battery Cabinet arrangements-

Each modules are interconnected in series or parllel according to the requirement and packed as a single large cabinet pack as shown below.

Battery pack arrangement:

Finally the overall battery pack after the arrangement of all cabinet connections with enclosure looks like this as shown below,

Vents holes are present with enclosure for cooling/heating the battery pack temperature according to its environment conditions.

The pack constructions are different for every manufacturers.

Below shown the battery pack constructios process of Tesla,BMW and Nissan Leaf.