Battery Pack Thermal Protector Segmentation for Low ESR
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Solution Overview
Problem
Rechargeable Li-Ion battery packs face challenges in reducing equivalent series resistance (ESR) without compromising safety, as existing thermal protectors either have high ESR or become unusable once tripped.
Innovation Solution
The battery pack design includes electronic switching devices that control current flow and separates the thermal protector from the circuit path, using a thermal protector with high impedance during normal conditions and low impedance during overtemperature, effectively reducing ESR by minimizing current through the protector.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a non-resettable thermal protector is used, then ESR is reduced, but the battery pack becomes unusable once tripped
Solution Approach 1:
The thermal protection function is segmented from the main circuit path. The thermal protector is placed in a separate parallel branch rather than in series with the cell, allowing it to monitor temperature without adding significant ESR to the main current path. This segmentation enables the use of high-impedance thermal protectors that would otherwise be unsuitable for series configuration.
Solution Approach 2:
The electronic switching devices act as intermediaries between the thermal protector and the main circuit. When the thermal protector detects overtemperature conditions, it triggers the electronic switches to open the main circuit, providing thermal protection without requiring the thermal protector itself to carry the main load current.
2Adaptability or versatility
If a resettable thermal protector is used, then the battery pack can be reused after tripping, but ESR increases
Solution Approach 1:
By segmenting the thermal protection circuit from the main power path and placing the thermal protector in a parallel branch, the resistance of the thermal protector no longer significantly impacts the ESR of the battery pack. This allows the use of resettable thermal protectors with higher impedance values without sacrificing battery performance.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This configuration reduces ESR, leading to longer battery operation times and enhanced safety by independently controlling temperature-dependent switches, preventing damage from overvoltage, overcurrent, and overtemperature conditions.
Implementation Method 1
the thermal protector 20 may be, for example, a thermal fuse, a thermal breaker or a positive temperature coefficient (PTC) thermistor
Data Source
AI summary
A battery pack comprising a power cell for providing power to a load or for receiving a charge from a charger, a first protection circuit for protecting from overvoltage and/or overcurrent conditions, and a second protection circuit for protecting from overtemperature conditions. The protection circuits independently control one or more electronic switching devices, through which passes substantially all of the current supplied by the power cell. When overvoltage and/or overcurrent conditions exist, the first protection circuit causes at least one of the switching devices to move to a non-conducting condition. Similarly, when an overtemperature condition exists, the second protection circuit causes at least one of the switching devices to move to a non-conducting condition.