On-board current measuring resistors for industrial applications

An on-board current measuring resistor in the battery management system (BMS) is used to precisely measure the electrical current flowing through the battery. The resistor generates a small but measurable voltage drop that is directly proportional to the flowing current according to Ohm's law U=R⋅IU=R⋅I. This voltage is recorded by a microcontroller or a special analog-to-digital converter (ADC) and used to monitor and control the charging process.

By precisely measuring the current, the BMS can determinethe state of charge (SoC) and state of health (SoH) of the battery. This is crucial for optimal battery life and efficient energy use, especially in electric vehicles and portable devices. A high-quality current measuring resistor with a low temperature coefficient and high stability ensures reliable data acquisition.

Another important feature is the low self-heating of the resistor, as high currents flow and power losses must be minimized. Modern electron beam welding processes and diffusion bonding improve the long-term stability of the resistor and minimize measurement errors due to thermal effects. In a well-coordinated BMS system, the on-board current measuring resistor makes a significant contribution to battery safety, performance optimization and increased efficiency.

High-precision on-board shunt resistors are made of special resistor alloys that are known for their high temperature stability and low resistance tolerances. Commonly used materials include manganin, a copper-manganese-nickel alloy, as well as nichrome (nickel-chromium) and special stainless steel variants. These materials are characterized by low thermal drift, which means that their resistance value remains constant even with temperature fluctuations.

An essential element of the design is the connection of copper to the resistor alloy, as the shunt is contacted directly with copper circuit boards or cables in most applications. Electron beam welding or diffusion bonding can be used to create a stable, long-term connection that reduces the occurrence of thermoelectric effects (thermo-EMF). These effects could otherwise lead to unwanted voltage deviations and impair measurement accuracy.

In addition, many precisionshunts are provided with a protective coating or surface treatment to prevent corrosion and material ageing. Particularly in demanding environments such as automotive and industrial electronics, the resistors must be mechanically robust, chemically resistant and electrically reliable. The choice of material is therefore crucial for the longevity, precision and efficiency of the on-board shunt resistor.

The temperature coefficient of resistance (TCR) describes how much the resistance value of a shunt resistor changes with temperature fluctuations. A low TCR value is crucial for high-precision current measurements, as it ensures that the resistance does not change due to environmental influences or self-heating. Resistors with manganese or other special alloys have a particularly low TCR value and are therefore widely used in precision applications.

The resistance tolerance indicates how much the actual resistance value can deviate from the nominal value. For highly accurate measurements in battery management systems, industrial electronics and automotive applications, tolerances in the range of ±0.1 % or better are required. If the deviation is too high, the measured currents may be inaccurate, which in turn affects the efficiency and safety of the entire system.

In addition, self-heating due to high currents affects both the temperature coefficient and the long-term stability of the resistor. By selecting materials with low thermal drift and minimal power loss, measurement errors can be reduced. The combination of low temperature coefficient and precise resistance tolerance thus ensures stable, reliable and accurate current measurement in sensitive applications.

On-board current measuring resistors are integrated directly into electronic circuits and enable compact, precise measurement of the current within the system. They are often used inbattery management systems, switching power supplies and automotive control systems where continuous and precise current monitoring is required. Due to their integration into the circuit board or system layout, they are thermally optimized to minimize self-heating and measurement errors.

Off-board current measuring resistors, on the other hand, are designed as external modules that are mounted outside the main circuit. They are particularly suitable for high-current applications where the heat generated needs to be dissipated more effectively. As they are often larger in size and made of resistant materials, they can measure very high currents with minimal resistance tolerance and are ideal for industrial energy measurement systems, battery storage solutions and power monitoring in electromobility.

The main difference therefore lies in the design, the thermal load capacity and the maximum current they can measure. While on-board current measuring resistors are optimized for compact systems with low to medium currents, off-board variants offer a more robust solution for high-current applications with better heat dissipation. Both variants are essential for precise and reliable power monitoring in modern electronic systems.