Project

This case study involves analyzing the battery pack sizing for an electric motorcycle with given motor requirements.

i. Cell Type Selection: Based on the average peak power of 23 kW, Lithium Iron Phosphate (LiFePO4) cells can be chosen due to their advantages:

• High thermal stability and safety.
• Long cycle life.
• Moderate energy density.
• Lower risk of thermal runaway.

Assumptions for Thermal Analysis:

• Cell temperature rise during operation is within a safe range (e.g., 5-10°C above ambient).
• Adequate ventilation and cooling provisions are in place.

ii. Cell Datasheet: Let's assume a LiFePO4 cell with the following characteristics:

• Nominal Capacity: 100 Ah
• Nominal Voltage: 3.2 V
• Internal Resistance: 0.1 Ohms
• Dimensions: 150mm x 100mm x 70mm
• Weight: 1.5 kg

iii. Battery Pack Voltage, Current, and Total Number of Cells:

Total battery pack voltage = Motor voltage / Cell voltage

Total battery pack voltage = 110 V / 3.2 V = 34.375, approximate to 34 cells in series.

Total current = Motor power / Motor voltage Total current = 40,000 W / 110 V = 363.6 A

Total number of cells = Total current / Cell capacity

Total number of cells = 363.6 A / 100 Ah = 3.636, approximate to 4 cells in parallel.

Maximum power transfer from the battery = Total current × Cell voltage × Number of parallel cells

Maximum power transfer = 363.6 A × 3.2 V × 4 = 4650.72 W, approximate to 4.65 kW.

iv. Battery Pack Volume:

The volume of the battery pack can be estimated by the dimensions of a single cell multiplied by the total number of cells: 

Battery pack volume = Cell volume × Total number of cells

Battery pack volume = (0.15 m × 0.1 m × 0.07 m) × 4 × 34 = 0.714 m⊃3;.

v. Battery Pack Weight and Total Energy:

Battery pack weight = Weight of a single cell × Total number of cells

Battery pack weight = 1.5 kg × 4 × 34 = 204 kg.

Total energy = Nominal Capacity × Nominal Voltage × Total number of cells

Total energy = 100 Ah × 3.2 V × 4 × 34 = 43.52 kWh.

vi. Cell-to-Cell Interconnection:

Interconnections can be achieved using bus bars or flexible copper connections depending on design and space constraints.

vii. Mechanical Stability and Safety Tests:

Tests to ensure mechanical stability and safety include:

• Vibration tests
• Impact tests
• Crush tests
• Thermal cycling tests
• Overcharge and overdischarge protection tests
• Short circuit tests

viii. Recycling Process:

Recycling involves:

• Collection and disassembly of battery packs.
• Separation of materials like metals, plastics, and electrolytes.
• Reuse or proper disposal of recovered materials.

ix. Thermal Runaway Prevention:

Thermal runaway is caused by:

• Overcharging
• External short circuits
• High operating temperatures Prevention involves:
• Effective thermal management systems.
• BMS monitoring and control.
• Use of stable chemistries (like LiFePO4).
• Implementing thermal fuses and cooling mechanisms.