Battery Charging via Low-Current Test Voltage Measurement
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Solution Overview
Problem
Batteries, such as lithium-ion batteries, cannot be accurately charged after being discharged beyond a certain voltage due to protection circuits disconnecting them from the load, making it unsafe to determine if the battery can be safely recharged, and existing methods fail to accurately measure the battery voltage in this state.
Innovation Solution
A method and system that apply a test current to the battery, measuring the voltage output including voltage drops across internal impedance and protection circuits, and only apply a charging current if the measured voltage is higher than a predetermined threshold, ensuring the cumulative voltage drop is minimal compared to the battery's voltage, thereby safely determining if the battery can be charged.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a test current is applied to measure battery voltage after protection circuit disconnection, then the battery voltage state can be determined, but the voltage measurement accuracy deteriorates due to voltage drops across internal impedance and protection circuits
Solution Approach 1:
The patent applies a test current parameter that is specifically constrained to be less than or equal to 10 mA, and in some embodiments even lower (e.g., 1 µA to 100 µA). By changing the current parameter to a very low value, the voltage drop across the internal impedance (V=IR) is minimized to less than 10% of the measured voltage, thereby maintaining measurement accuracy while still being able to determine the battery voltage state.
Solution Approach 2:
The patent replaces direct voltage measurement (which would draw significant current and cause voltage drops) with an indirect measurement method. Instead of measuring voltage directly under load, the system applies a minimal test current and measures the resulting voltage, effectively substituting a mechanical/electrical direct measurement approach with a more refined indirect measurement technique that minimizes disturbance to the system.
2Reliability
If a high test current is used to ensure reliable voltage measurement, then the measurement reliability improves, but the battery may be damaged or the measurement becomes inaccurate due to excessive voltage drops
Solution Approach 1:
The patent changes the current parameter from high values (which would cause damage) to very low values (≤10 mA, preferably µA range). This parameter change ensures that the test current is sufficient to produce a measurable voltage signal for reliable determination of battery state, while simultaneously being low enough to prevent battery damage and minimize voltage drops that would compromise measurement accuracy.
Solution Approach 2:
The patent introduces a protection circuit as an intermediary element between the voltage source and the battery. This protection circuit includes current limiting functionality that mediates the interaction between the measurement system and the battery, ensuring that the current applied never exceeds safe levels (≤10 mA) while still enabling reliable voltage measurement for determining battery chargeability.
3Reliability
If the protection circuit remains in disconnect state, then the battery is protected from over-discharge, but the inability to accurately measure voltage prevents determination of safe recharging conditions
Solution Approach 1:
The patent applies a preliminary test current (≤10 mA) to the battery while the protection circuit is in disconnect state, before attempting to recharge. This preliminary action serves two purposes: it re-establishes electrical connection through the protection circuit, and it enables accurate voltage measurement by minimizing voltage drops. Based on this preliminary measurement, the system can then determine whether the battery voltage exceeds the threshold (e.g., 2.4V per cell) for safe recharging.
Solution Approach 2:
The patent implements a feedback mechanism where the voltage measurement obtained from applying the test current is used to determine the next action. The measured voltage is compared against a predetermined threshold, and this feedback determines whether the protection circuit should be reset and recharging should commence. This closed-loop feedback ensures that recharging only occurs when safety conditions are confirmed.
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 approach allows for accurate determination of the battery's voltage state after protection circuit disconnection, ensuring safe charging and minimizing the impact of internal and external impedance on voltage measurements, thus extending battery life and preventing unsafe recharging.
Implementation Method 1
measuring a voltage output, wherein the voltage output comprises a voltage of the cell and a voltage drop, induced by the test current, across at least an internal impedance of the battery
Data Source
AI summary
A method of charging a cell of a battery includes the steps of: applying a test current to an input terminal of the battery; measuring a voltage output, wherein the voltage output is comprised of a voltage of the cell and a voltage drop, induced by the test current, across an internal impedance of the battery; and applying a charging current to the input terminal of the battery if the measured voltage output is higher than a predetermined voltage, wherein the charging current is greater than the test current.