Project 1 Mechanical design of battery pack
Aim
prepare a battery pack with capacity 18KWh
Theory
Battery pack
A battery pack is a set of any number of identical batteries or invidual cells. They may be configured in a series, parallel or a mixture of both to deliver the desired voltage, capacity or power density. A battery pack consist of battery module and can be further disassembled as cells. The cells are interconnected in series and parallel configuration to form battery pack. Terminal voltage and capacity of the battery pack is the voltage and capacity of cells added accourding to the configuration.
A battery cell consists of five major components: electrodes – anode and cathode, separators, terminals, electrolytes, and a case or enclosure. For automotive applications, there are different types of cells used Individual battery cells are grouped into a single mechanical and electrical unit called a battery module. The modules are electrically connected to form a battery pack. Differnt types of cell accourding to shape are cylindrical and prismatic. And in the prismatic there are pouch type and hardcase.
cells are conneceted in series or parallel configuration using spot welding, laser welding, soldering
Spot welding
It is type of electric resistance welding used to weld various sheet metal products, through a process in which contacting metal surface points are joined by the heat obtained from resistance to electric current. The process uses two shaped copper alloy electrodes to concentrate welding current into a small "spot" and to simultaneously clamp the sheets together. Work-pieces are held together under pressure exerted by electrodes. Typically the sheets are in the 0.5 to 3 mm (0.020 to 0.118 in) thickness range. Forcing a large current through the spot will melt the metal and form the weld. The attractive feature of spot welding is that a large amount of energy can be delivered to the spot in a very short time (approximately 10–100 milliseconds). This permits the welding to occur without excessive heating of the remainder of the sheet. The amount of heat (energy) delivered to the spot is determined by the resistance between the electrodes and the magnitude and duration of the current. The amount of energy is chosen to match the sheet's material properties, its thickness, and type of electrodes. Applying too little energy will not melt the metal or will make a poor weld. Applying too much energy will melt too much metal, eject molten material, and make a hole rather than a weld. Another feature of spot welding is that the energy delivered to the spot can be controlled to produce reliable welds
laser welding
Laser beam welding (LBW) is a welding technique used to join pieces of metal or thermoplastics through the use of a laser. The beam provides a concentrated heat source, allowing for narrow, deep welds and high welding rates. The process is frequently used in high volume and precision requiring applications using automation, as in the automotive and aeronautics industries. It is based on keyhole or penetration mode welding.
The batteries are interconnected using strips which are selected according to the need.
The battery modules is connected to BMS and Cooling system is imparted in it.
The battery models are then pu together and battery pack is obtaind and the is installed in the vehicle.
ANR26650M1-B
cell specifications
nominal voltage = 3.3v
capacity = 2.5Ah
energy = 8.25Wh
specific power = 2600
calculations
let us assume voltage as 72v
therefore current = 18000Wh/72 = 250Ah
cells in series = 72/3.3 = 22
cells in parallel = 250/2.5 = 100
The battery pack will be of 22S100P combination
There will be 2200 no:of cells
weight of battery (cells only) = .076*2200 = 167Kg
let us consider the cell dia as 26mm and between each adjacent cell there is a 4mm gap
100 parallel cells are kept in 2 rows of 50 each and forms a battery set
this is connected in series 22 times
length of pack = 30*50 = 1500mm
breadth = 30*44 = 1320mm
height = 70mm
