Battery Ingress Detection Circuit Using NTC and Open Capacitor
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Solution Overview
Problem
Existing lithium-ion battery packs in electronic devices face damage from water ingress due to insufficient sensitivity and cost-effectiveness of current water detection mechanisms, leading to corrosion and circuit failure.
Innovation Solution
A self-contained battery protection system that includes a capacitor with open metal gaps and a negative thermal temperature coefficient (NTC) thermistor, which detects changes in resistance or voltage drop caused by water ingress, triggering a shutdown or permanent disconnection to prevent further damage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If mechanical seals and water detection mechanisms are applied to prevent water ingress, then battery protection is improved, but device complexity and cost increase
Solution Approach 1:
The patent combines the water detection function with the existing temperature sensing NTC thermistor by coupling a capacitor in parallel with it. This merging allows the same circuit to detect both temperature and water ingress (through capacitance changes when water bridges the capacitor plates), reducing overall system complexity while maintaining protection reliability.
Solution Approach 2:
The NTC thermistor circuit is designed to serve multiple functions: temperature monitoring and water detection. By adding a capacitor in parallel, the circuit gains the ability to detect water ingress through capacitance changes, making the same circuitry universal for both thermal management and water protection without requiring separate dedicated sensors.
2Reliability
If mechanical seals are applied to prevent water ingress, then battery protection is improved, but cost increases
Solution Approach 1:
The patent uses inexpensive electronic components (capacitor and NTC thermistor) that can be easily integrated into the battery circuit to detect water ingress. This approach replaces or supplements expensive mechanical seals with affordable electronic sensing, significantly reducing manufacturing costs while maintaining effective water detection and protection capabilities.
Solution Approach 2:
The patent replaces mechanical water sealing mechanisms with an electronic detection system based on capacitance changes. When water ingress occurs, it bridges the capacitor plates, changing the capacitance value, which is detected by the control circuit. This substitution eliminates the need for complex mechanical seals, reducing both cost and manufacturing complexity.
3Measurement precision
If existing water detection mechanisms are applied, then some water ingress detection is achieved, but sensitivity to water detection is insufficient
Solution Approach 1:
The patent places the capacitor in direct proximity to the battery cells and couples it in parallel with the NTC thermistor. This local positioning ensures that when water ingress occurs, it immediately affects the capacitor plates, producing a detectable capacitance change. The local quality of this arrangement maximizes detection sensitivity without requiring complex distributed sensor networks.
Solution Approach 2:
The patent detects water ingress by monitoring changes in capacitance parameter of the capacitor. When water bridges the capacitor plates, the capacitance value changes, which is detected by the control circuit. This parameter-based detection method provides high sensitivity to water presence while using simple, low-cost electronic components, avoiding the need for complex detection systems.
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 solution provides a simple and cost-effective method to detect water ingress in lithium-ion battery packs, effectively preventing damage by accurately distinguishing between temperature changes and water exposure, thereby protecting the battery from corrosion and circuit failure.
Implementation Method 1
a capacitor coupled in parallel with the NTC thermistor. The capacitor has an open area and two electrodes that are at least partially exposed via the open area
Implementation Method 2
a negative thermal temperature coefficient (NTC) thermistor
Data Source
AI summary
This application is directed to an electronic device powered by one or more rechargeable battery cells. The electronic device includes a first negative temperature coefficient (NTC) thermistor proximate to the battery cells, and an open capacitor coupled in parallel with the NTC thermistor. The open capacitor has an open area and two electrodes that are at least partially exposed via the open area and electrically isolated. The electronic device further includes a control circuit coupled to the NTC thermistor and the open capacitor. The control circuit is configured to detect a voltage drop across the NTC thermistor and the open capacitor if conductive liquid enters the open area of the capacitor and electrically connects the two electrodes that are at least partially exposed via the open area.