Differential Battery Voltage Measurement for Fast SDR and IR Testing
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Solution Overview
Problem
Existing battery manufacturing processes face challenges in accurately measuring self-discharge rate (SDR) and internal resistance (IR) of batteries within a short time frame, necessitating lengthy aging periods for precise voltage measurements, which hampers production efficiency and increases space and cost.
Innovation Solution
A battery testing apparatus utilizing a difference voltmeter with a reference voltage generator and operational amplifiers to measure ΔOCV and ΔIR, enabling accurate determination of SDR and IR through differential voltage calculations, reducing the aging time required for precise measurements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a battery's open-circuit voltage is measured and the battery is stored for a long period to calculate self-discharge rate, then the measurement accuracy is improved, but the production time is increased
Solution Approach 1:
The system performs preliminary formation charging and voltage stabilization before the self-discharge measurement begins. The battery is charged to a target voltage and held there until the voltage change rate falls below a threshold, ensuring the battery is fully stabilized before measurement. This preliminary action eliminates the need for long aging periods.
Solution Approach 2:
The system continuously monitors the battery voltage during formation and self-discharge measurement, using feedback control to determine when the battery has reached stable state. The measurement process is dynamically adjusted based on real-time voltage change rates, allowing the system to automatically terminate measurements when sufficient stability is achieved, rather than using fixed long aging periods.
2Measurement precision
If a battery's open-circuit voltage is measured and the battery is stored for a long period to calculate self-discharge rate, then the measurement accuracy is improved, but the production efficiency is reduced
Solution Approach 1:
The system performs preliminary formation charging and voltage stabilization before the self-discharge measurement begins. The battery is charged to a target voltage and held there until the voltage change rate falls below a threshold, ensuring the battery is fully stabilized before measurement. This preliminary action eliminates the need for long aging periods.
Solution Approach 2:
The system continuously monitors the battery voltage during formation and self-discharge measurement, using feedback control to determine when the battery has reached stable state. The measurement process is dynamically adjusted based on real-time voltage change rates, allowing the system to automatically terminate measurements when sufficient stability is achieved, rather than using fixed long aging periods.
3Device complexity
If traditional voltage measurement methods are used, then the measurement process is simple, but the measurement accuracy for small voltage differences is insufficient
Solution Approach 1:
The system introduces an intermediary reference voltage (Vref) that is closely matched to the battery voltage during formation. By measuring the small difference between the battery voltage and this intermediary reference voltage, rather than measuring the absolute battery voltage directly, the system achieves much higher measurement precision for small voltage changes while keeping the measurement system relatively simple.
Solution Approach 2:
The system changes the measurement parameter from absolute voltage measurement to differential voltage measurement. By using a reference voltage that tracks the battery voltage and measuring only the difference, the system transforms a large-signal measurement problem into a small-signal measurement problem, which can be solved with higher precision using standard measurement techniques.
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
The apparatus significantly enhances the accuracy of SDR and IR measurements, allowing batteries to be sorted into consistent groups in a fraction of the time, thereby improving production efficiency and reducing space and cost.
Implementation Method 1
a reference voltage generator (RVG) configured to generate a reference voltage and output the reference voltage via its first lead
Implementation Method 2
a first operational amplifier (OPA), the first OPA has a first input lead to be connected to a first terminal of an object to be measured, a second input lead connected to the first lead of the RVG, and the first OPA is configured to output via its output lead a difference voltage representing a difference between a voltage of the object and the reference voltage
Implementation Method 3
an analog-to-digital converter (ADC) configured to receive the difference voltage from the output lead of the first OPA and convert the difference voltage from analog signal to digital signal
Data Source
AI summary
A difference voltmeter (DVM) is used in a battery testing apparatus for determining values of open-circuit voltage, self-discharge, self-discharge rate and internal resistance of batteries. A reference voltage Vref is generated. A difference OCV relative to Vref is determined at times t1 and t2 as ΔOCV1 and ΔOCV2. The SD for a battery is determined as (ΔOCV2−ΔOCV1), and the SDR is determined as SD/(t2−t1). The IR of a battery is determined by measuring voltage at two levels of direct current and calculating IR as equal to (ΔV2−ΔV1)/(I2−I1). The smaller FSR of the DVM allows a more accurate measurement of OCV, which allows the time for determining the SDR to be reduced.