Project 1 Mechanical design of battery pack

Introduction:-

battery pack :- Battery is an electric device which is an assembly of electrical cell which contain the stored chemical energy convert into the elctric energy. each cell has positive terminal cathode and negative terminal cathode. these cell combine each other by series and parallel connection and form a battery.

1) Battery pack calculation:- To construct the battery pack of having capacity 18 KWh, we must use the cell is ANR26650M1-B which is manufacture by A123 system. The feature of cell are it deliver high power and energy density combined with excellent safety performance and excessive life cycling in light weight and more compact package.The specification of the cell are given in following image :-

Energy :- For battery pack , the energy required is about 18 KWh. The energy of cell is 8.25Wh.

Number of cell (N) :- The number of cell required for battery is calculate by the formula are : For construct battery pack of energy is 18 KWh, we need to arrange the cell in series and parallel combination. In case of series connection the battery voltage is sum of voltage of individual cell and current remain same and also the battery capacity remain same. In case of parallel combination the voltage of battery is same but the capacity is accumulate.

Nominal voltage of each single cell = 3.3 V

So the number of cell connected in series can be consider as 48. Assume that we connect 48 cell in series then the voltage obtained from these series module is calculate as :-

Voltage obtained = number of cell connect in series * Nominal voltage

= ( 48 * 3.3 )

= 158.4 V ( Voltage obtained in series combination)

Now, we must need to calculate the parallel connection of cell :- Assume that 48 cell connect in parallel.

Current = number of cell connect in parallel * capacity

= ( 48 * 2.6 )

= 124.8 A

So the cell connect the combination in that manner such as follows:-

Cell connection in battery :- 48s48p

2) Battery capacity :- Now calculation of battery capacity are as follows :

In case of series connection :- No of cell * voltage = 48 * 3.3 = 158.4 V

In case of parallel connection :- No of cell * capacity = 48 * 2.6 = 124.8 A

From these we get capacity = voltage * current = 158.4 * 124.8 = 19768.32 ( 19 KWh ) We need to 18 KWh battery energy but from this combination we get 19 KWh but the excessive energy is useful for battery pack performance.

3) Range :- The range of battery pack in case vehicle run in km is calculate as:- Assume that Powertrain energy consumption = 129Km/hr at 70% efficiency. The powertrain consists of the power source and all of the components that convert the battery power into movement of the vehicle.

Range = capacity / Energy consumed by per Km

= 19000 / 129

= 147.28 Km So ,the vehicle able to cover 147 Km distance.

3) Battery pack Dimentions :- ANR26650M1-B cell having a dimension about its height and size specifiation given in above picture such as :-

Diameter	25.96 +/- 0.5 mm
Length	65.15 +/- 0.5 mm
Mass	76 g +/ 1.0 g

From these single cell size we need to calculate the battery pack size and the casing size required for battery pack also be calculate . The calculation of casing as follows :-

Length of casing =[ Number of cell * ( Cell diameter )+ Gap between two cell + Gap between two module + Clearance at both side ]

= [ 8 * (30) + 5 (4) + 6 (3) + 20 ]

= 298 mm ~ 300 mm

So the casing length used for the battery pack is 300 mm.

Breadth of casing = [ Number of cell * (Cell diameter) + Gap between two cell + Clearance at both side ]

= [ 6 * 30 + 5 (5) +20]

= 225 mm

so the casing breadth used for battery pack is 225 mm.

Height of casing = [ Height of cell + Margin for wiring, holders, strips ]

= [ 65+ 35 ]

= 100 mm

Height of casing for battery pack is 100 mm.

4) weight of battery =

Cell weight = 76g

Number of cell = 2304

Battery pack weight = [Cell weight * Number of cell + accessories weight]

= (76 * 2304 )+ 5

= 175 Kg

5) Battery pack assembly = The component required for construct a battery pack such as 2304 cell, cell holder , nickel strip , solder gun ,PVC heat sink film , spot welder, connector , soldering wire.

Material required for build a battery pack

Step 1 :- To construct battery pack , first gathe all material required for battery pack

step 2 :- first choose appropriate cell holder for types battery pack .

Cell holder Matrix :-

Place all the cell in cell holder from both upper and bottom side. put gasket in positive side of cell.

Step 3 :- after that choosing a right strip for battery pack. Connect the cell by using nickel strip.there are two types of nickel strip available :- 1)Nickel plated steel strip 2) pure nickel strip . it has much lower resistance. Low resistance means, less heat generation during the charging and discharging, which leads to longer useful battery life.

Step 4 :- The reason we spot weld because it securely joins the cells together without adding much heat to them.There are two grades of spot welders currently available in the market: hobby grade and professional grade.

Before connecting the cells in parallel, first, check the individual cell voltages. For paralleling the cells, the voltage of each cell should be near to each other, otherwise, a high amount of current will flow from the cell with a higher voltage to the cell with a lower voltage. This can damage the cells and even result in fire on rare occasions.

step 5:-after connection and soldering nickel strip , stick PVC heat sink film to cell and solder balancing wire to terminal

these is the pvc heat sink material

Step 6 :- Adding a Battery management system. connect balancing wire pin to BMS and glue it .A battery management system (BMS) is an electronic system that manages a battery pack and the main functionalities are :- i) Monitors all of the parallel groups in the battery pack and disconnect it from the input power source when fully charge.

ii) Balance all the cells voltage equally.

iii) Doesn't allow the pack from over-discharge.

spot weld the nickel strips to the BMS or solder it to the PCB pad. First, apply soldering flux to the PCB pads and end of the nickel strips. After that tin all the pads by applying a little amount of solder and then solder them together.

step 7 :- Connect the supply wire by the soldering and cover the total bttery pack by plastic sheet for the protection . Place the total battery pack in enclosure for safety of battery. The battery pack has all-around exposed nickel strips, to avoid any accidental shorting used an enclosure for it.The enclosure has two parts: The main Body and top lid.

these types of enclosure usedfor car battery pack:-

The battery pack is ready with enclosure.

Model of battery pack:-

Analysis from cell level to battery pack :-

Parameter	cell level	Battery pack level
Voltage	3.3 V	158.4V
Output Energy	0.00825 KWh	19 KWh
Dimension	30mm (Diameter)*65mm (Length)	300mm (Length)*200mm(breadth)*100mm (height)
Range	0.064	147.28 Km
Architecture	cylindrical in shape	Square in shape (battery pack)
Weight	76g	175 Kg

Note :- The image add is not actual image of design battery pack it just the understanding procedure to build battery pack. But the by follows the step you can build battery pack.