Battery Charge Voltage Step-Down to Prevent Overcharge Swelling
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Solution Overview
Problem
Rechargeable batteries, such as lithium-ion batteries, face the issue of swelling due to overcharge, leading to potential fires and damage when kept on a charger for extended periods, as current technologies fail to prevent continuous charging beyond full capacity.
Innovation Solution
A method utilizing a microcontroller unit (MCU) with a bit array to monitor battery voltage against a threshold, shifting bits to create a sliding window, and stepping down the charger voltage when the battery is consistently above the threshold, thereby preventing overcharging.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the battery is kept on a charger for extended periods to ensure full charging, then the charge level is maintained at maximum, but battery swelling occurs due to continuous trickle current
Solution Approach 1:
The system performs preliminary monitoring of battery voltage and sets a history of voltage exceedances before taking protective action. By tracking voltage levels over a predetermined time period and counting exceedances above the threshold voltage, the system prepares to terminate charging before swelling can occur, rather than reacting after damage begins
Solution Approach 2:
The system continuously monitors battery voltage and provides feedback by comparing it against a threshold voltage. The fuel gauge IC and charger IC exchange information about charge state and voltage levels, creating a closed-loop control system that adjusts or terminates charging based on real-time battery conditions, preventing the harmful continuous trickle charging
2Productivity
If charger ICs and fuel gauge ICs terminate charge current when battery is full, then charging efficiency is improved, but they continue to supply trickle current which causes swelling over time
Solution Approach 1:
The system establishes predetermined thresholds and time periods in advance to determine when trickle charging should be terminated. By setting a voltage threshold and a time window for monitoring, the system prepares criteria for when to stop charging completely, rather than continuing indefinitely
Solution Approach 2:
The fuel gauge IC autonomously monitors battery voltage and communicates charge state to the charger IC, enabling the charging system to self-regulate. The system uses its own internal resources (voltage monitoring, bit array memory, counter) to determine when to terminate charging without external intervention
3Device complexity
If a simple voltage threshold monitoring system is used, then device complexity is reduced, but it cannot distinguish between temporary voltage spikes and sustained overcharge conditions
Solution Approach 1:
The system pre-configures a history array with a predetermined number of entries corresponding to a time window, and establishes a threshold for the number of voltage exceedances required to trigger termination. This preliminary setup enables the system to filter out temporary spikes by requiring multiple exceedances within the time window
Solution Approach 2:
The monitoring period is segmented into discrete sampling intervals, with each interval represented by a bit in the history array. By dividing the time window into multiple segments and requiring a threshold number of exceedances across these segments, the system achieves more precise detection while maintaining simple hardware implementation
Data Source
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AI summary
An indexed sequence of bits in a buffer is allocated for tracking a battery charging state. The indexed sequence of bits has a first number of bits. A battery voltage of a rechargeable battery is sampled at a sampling rate. For each sampled battery voltage, the battery voltage is compared with a voltage threshold. A next bit position in the indexed sequence of bits is identified. In accordance with a determination that a comparison result is true, a predefined first value is added to the next bit position. A second number of bits that are filled with the predefined first value is determined. A ratio between the second number and the first number is also determined. In accordance with a determination that the ratio exceeds a threshold step-down ratio, a battery charge voltage is stepped down. The rechargeable battery is charged to a step-down voltage.