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Battery Pack Design - Lesson Summary

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MECHANICAL DESIGN

The mechanical design of a battery pack leads to safe and cost effective elements that are lightweight and highly reliable. The following characteristics need to be met in the mechanical design:

◦ Safe structure for extreme conditions.
◦ Cost, productivity and reliability.
◦ Ease of assembly and service
◦ Aesthetics, compactness, and lightweight.

Various factors considered while designing a battery pack:

• Material selection using a Material Index
• Loading conditions of the base plate, end plate and side strips.
• Bus bar and outer casing development.
• For base plate and end plates, use Kirchoff’s equation for thin flat plates.

THERMAL DESIGN

A good Thermal Design will improve pack efficiency, mitigate thermal accidents, and increase cell/pack life.

Energy flow (or Heat Transfer) occurs when there is a temperature gradient. There are three modes of heat transfer: Conduction, Convection, and Radiation.

There are two types of thermal management systems:

• Active Systems
◦ Air
◦ Liquid
◦ Refrigerant
◦ Hybrid
• Passive Systems
◦ PCM
◦ Embedded Micro Channels.

Passive thermal management systems are preferred but if one is not possible, choose an active system that is simple and robust, with low power consumption, and easily serviceable.

Material for a thermal system should be based on:

• Thermal properties
• Mechanical stability
• Cost

ELECTRICAL DESIGN

Busbars should be designed with:

• Average current density of 5 A/mm2
• Sufficient cooling by natural convection.
• Easy manufacturability and assembly.
• Cost-effective material solutions.

Electrical System should have:

• Minimized voltage drop wherever possible.
• Sufficient electrical insulation to prevent accidents and mitigation.
• Mechanically rigid.

Busbars joining methods preferred with:

• Highest mechanical strength.
• Minimal contact resistance.
• Easy weldability.

BMS DESIGN

A well-designed Battery Battery Management System (BMS) should:

• Maintain cell/pack operation limits.
• Prevent safety concerning events.
• Control thermal systems.
• Communications and diagnostics.

Battery Pack Protection.

BMS electronics and software are an integral part of an overall risk-management strategy. The following undesirable conditions and events are addressed:

• Excessive current during charging and discharging.
• Short circuit scenarios.
• Over-voltage or under-voltage.
• Loss of isolation
• Abuse