Battery Current Sensor Thermal Compensation for Vehicle Shunts
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Solution Overview
Problem
Existing devices for measuring battery current in vehicles face challenges due to the wide range of current variability, high noise levels, and temperature variations, which affect the signal-to-noise ratio and sensitivity of electronics, particularly when using low-resistance shunts like copper plates.
Innovation Solution
A device and method that employ an iterative or non-iterative approach to calculate battery current using a thermal model, compensating for resistance variations by measuring temperature changes over time, and using a weighted-mean value or direct calculation based on temperature and power dissipation, without the need for direct temperature measurement.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If a low-resistance shunt (e.g., copper plate) is used to measure high battery current, then power dissipation is reduced, but signal-to-noise ratio and measurement sensitivity deteriorate
Solution Approach 1:
The measurement function is segmented into two independent parts: the shunt handles only current conduction with minimal resistance (reducing power dissipation), while a separate sensing circuit measures the voltage across the shunt (improving signal-to-noise ratio). This segmentation allows each component to be optimized for its specific function without compromise.
2Loss of energy
If a low-resistance shunt is used to contain power dissipation, then energy loss is reduced, but the detected voltage signal becomes extremely small (e.g., 1 μV for 10 mA noise)
Solution Approach 1:
An instrumentation amplifier serves as an intermediary between the shunt and the measurement system. This amplifier provides high input impedance to avoid loading the shunt, differential amplification to reject common-mode noise, and gain amplification to boost the small voltage signal to a measurable level, thereby solving the detection difficulty without increasing shunt resistance.
3Measurement precision
If temperature compensation electronics are added to correct resistance variations, then measurement accuracy across temperature ranges is improved, but device complexity increases
Solution Approach 1:
A temperature sensor monitors the shunt temperature and feeds this information to a microcontroller, which calculates the resistance variation based on pre-stored temperature coefficients and compensates the measurement in real-time. This feedback mechanism achieves temperature compensation through software algorithms rather than complex hardware circuits, reducing overall device complexity.
Solution Approach 2:
The system changes the measurement parameter from direct voltage measurement to temperature-corrected voltage measurement. By measuring temperature and using it to adjust the resistance value in calculations, the system compensates for thermal effects without requiring complex temperature-independent materials or additional sensing elements.
4Productivity
If the shunt resistance is made extremely low (e.g., 100 μΩ) to handle high current, then current handling capability is improved, but noise sensitivity increases significantly
Solution Approach 1:
The instrumentation amplifier acts as an intermediary that isolates the low-resistance shunt from the high-impedance measurement circuitry. It provides galvanic isolation and impedance matching, preventing noise from coupling into the measurement system while maintaining the low resistance needed for high current handling.
Solution Approach 2:
The patent replaces the mechanical/material solution of using high-resistance materials (like manganin) with an electronic solution combining low-resistance copper shunt plus electronic noise filtering and amplification. This substitution allows optimal electrical properties (low resistance) to be maintained while electronic circuits compensate for the resulting noise sensitivity.
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
Enables precise and cost-effective measurement of battery current, improving accuracy and reducing noise interference across varying temperatures and current ranges.
Implementation Method 1
the variation in temperature is due to the power dissipated by the current that flows through the resistive element
Implementation Method 2
The determination of the temperature is carried out in any suitable way, for example using thermocouples or thermistors or sensing circuits
Data Source
Figure 1
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AI summary
A device for measuring the current of a battery on board a motor vehicle comprises a resistor or shunt constituted by a copper plate (4,4') having a predetermined known resistance and connected in series between a terminal (1) of the battery and a conductor cable associated thereto. An electronic circuit for measuring the current determines the battery current by detecting the voltage across the shunt. The circuit comprises electronic compensation means, which are designed to correct the measured value of current taking into account the variations of resistance of the shunt that arise as the temperature varies, on the basis of a thermal model that represents the relationship between the power dissipated in the shunt and the thermal condition thereof.