Project 1 Mechanical design of battery pack

AIM

To Prepare a detailed battery pack drawing along with its enclosure of 18 KWh Capacity and ANR26650M1-B.

DESCRIPTION

Battery cell: A cell refers to a single anode and cathode separated by electrolyte used to produce a voltage and current.

Battery module: a battery Module is a combination of two or more cells in series or parallel with protective shield to protect cells from external environment.

Battery Pack: this is the final shape of the battery system installed. Composed of modules and various control/protection systems including a BMS(battery management system), a cooling system, etc.

To increase the Ampere-hour capacity of battery cells need to be connected in parallel and to increase the voltage capacity of the battery cells need to be connected in the series.

Mechanical design of the battery doesn’t only have connection but also arrangement of cells, total weight of the battery, designing the cover of battery pack battery pack.

CALCULATIONS

The total capacity of battery required is 18 KWh

The cell used is ANR26650M1-B

Electrical specifications of a cell

1. Nominal Capacity 2600mAh (0.2C, 2.75V discharge)
2. Charging Voltage 4.2 ±0.05 V
3. Nominal Voltage 3.7V
4. Charging Method CC-CV (constant voltage with limited current)
5. Charging Current Standard charge: 1300mA Rapid charge : 2600mA
6. Charging Time Standard charge : 3hours Rapid charge : 2.5hours
7. Max. Charge Current 2600mA
8. Max. Discharge Current 5200mA
9. Discharge Cut-off Voltage 2.75V

Mechanical specifications

1. Cell Dimension Diameter(max.) : Φ 18.40 mm Height(max.) : 65.00 mm
2. Cell weight : 76 grams

Click here to get the data sheet of cell

Assumptions

1. Total voltage required= 98 V
2. No of battery modules= 3

Number of cells required = total capacity required / capacity of each cell

=18000/(3.3*2.5)

=18000/8.25

=2181.18

Lets consider 2200 cells required which will also increase the reserve capacity for losses

No of cells connected series= Total Voltage required / each cell nominal voltage

= 98/3.3

= 29.67 cells

= 30 cells

No of cells connected in parallel= total cells required / cells in series

= 2200/30

= 73.33 cells

≈75 cells

Now lets Calculate Actual capacity of battery in Ah and KWh with above configurations

Capacity in Ah= no of cells parallel * Ah rating of cell

= 75*2.5

= 187.5 Ah

Voltage capacity= no of cells in series * Voltage rating

=30*3.3

=99 V

Capacity in KWh=(187.5*99)/1000

=18.56 KWh

Actual number of cells required = cells in parallel * cells in series= 75*30=2250 cells

Now lets divide total cells in battery pack to different battery modules

Lets consider three modules need to be connected in series

The each module will have 75 cells in parallel and 10 cells in series therefore 3 modules in series can meet requirement of total capacity.

Total number of cells in a module will be 750 cells

Which means a battery module can be rated as 10S75P

Total battery pack is of 30S75P rated

Connections of modules in battery pack

RESULTS

Prepared a detailed battery pack drawing along with its enclosure of 18 KWh Capacity and ANR26650M1-B.