Battery Pack Overcurrent Protection with Thermostat Detection
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Solution Overview
Problem
Lithium ion battery packs used in electric tools face challenges with large and costly protective elements for high current capacity, such as FETs and fuses, which are difficult to reuse and lack clear indication of self-reset type elements' status, posing safety concerns during overcurrent events.
Innovation Solution
A battery pack design incorporating a current control element with a thermostat and heat-sensitive resistance element connected in parallel, along with a detection unit that outputs an open signal when the thermostat contacts open, and a control unit that maintains a discharge prohibition state until the contacts return to a safe state.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of repair
If a self-reset type element is used for overcurrent protection, then the protective element can be reused after resetting, but it is difficult for users to recognize the timing when the contact returns and the discharging becomes possible
Solution Approach 1:
The patent employs visual indicators that change color or illumination state to communicate the status of the self-reset protective element. When the contact returns and discharging becomes possible, the indicator provides clear visual feedback through color change or light emission, allowing users to easily recognize the status without needing to understand internal circuit operations.
2Reliability
If a fuse is used for overcurrent protection, then the battery is protected from overcurrent damage, but the fuse cannot be reused after it is fused
Solution Approach 1:
The patent implements a self-reset protective element that automatically resets after tripping due to overcurrent. The element uses a heat-sensitive resistance component (PTC thermistor) that returns to its low-resistance state when cooled, enabling automatic recovery without manual replacement. This self-service mechanism maintains reliable overcurrent protection while eliminating the need for fuse replacement.
3Reliability
If a breaker is used for overcurrent protection, then the battery is protected from overcurrent damage, but manual resetting is required after the breaker operates
Solution Approach 1:
The patent employs a self-reset protective element using a PTC thermistor that automatically returns to its conducting state after the overcurrent condition is removed and the element cools down. This eliminates the need for manual resetting operations required by traditional breakers, while maintaining reliable overcurrent protection through the inherent thermal characteristics of the PTC material.
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 enhances safety by preventing overcurrent damage to the battery and providing clear visual feedback on the battery pack's status, ensuring the electric tool does not suddenly restart after an overcurrent event.
Implementation Method 1
a heat sensitive resistance element (Positive Temperature Coefficient: PTC element, also called PTC thermistor) whose resistance increases rapidly when exceeding an arbitrary temperature
Implementation Method 2
a thermostat... in which a bimetal is bent when a predetermined temperature is exceeded
Data Source
AI summary
There is provided a battery pack including a current control element which is inserted in a discharge current path, and in which a thermostat and a heat sensitive resistance element whose resistance value increases in response to an increase in temperature are connected in parallel; and a detection unit that outputs an open signal indicating the opening of the contacts when it is detected that contacts of the thermostat are opened.