Complete Guide To Selection And Application Of Metal Alloy Shunt Resistors

Metal alloy shunt resistors are widely used for precise current monitoring and power management due to their extremely low resistance values, high precision, and excellent thermal stability. 

What is a Metal Alloy Current Sensing Resistor？

Metal alloy shunt resistors are passive components that use ultra-low resistance metal alloy foils or wires to achieve precise current measurement by detecting the tiny voltage drop at both ends. Common materials include copper-nickel (CuNi), copper-chromium (CuCr), nickel-chromium (NiCr), etc., which can maintain the characteristics of small temperature coefficient, good heat dissipation and long service life under high current environment. Core function: Convert current into measurable small voltage signals for precise collection by ADC, operational amplifier and other circuits. main advantage

• Ultra-low resistance value (mΩ level)
• High precision (±0.1% to ±1%)
• Low temperature coefficient (±10 ppm/℃ to ±50 ppm/℃)

Unveiling Materials and Structures

Common types of metal alloys

Encapsulation and structural form 

• Metal foil type: Alloy foil is adhered to ceramic or epoxy substrates, suitable for high-precision and low-temperature drift applications.
• Metal film type: A metal film is deposited on an insulating substrate by sputtering process, which can better control thickness and resistance value;
• Lead type: Sealed after winding with alloy wire, it has a high power density and is suitable for high-current detection.
• Bolt type: Designed with bolt holes, it can be directly hard-connected to the busbar or terminal block, and has extremely strong heat dissipation and current carrying capacity.

Analysis of Key Performance Parameters

Power Rating

• It indicates the maximum dissipated power at a specific ambient temperature, such as 1 W, 3 W, and 10 W.
• When selecting the model, sufficient margin should be left (it is recommended to be ≥ 150% of the actual power).

Resistance Value

• Commonly 0.1 mΩ to 100 mΩ; The greater the current, the lower the resistance value to reduce power consumption.

TCR

• The unit is ppm/℃. The lower it is, the smaller the influence of temperature change on the resistance value.

Tolerance

• ±0.1%, ±0.5%, ±1.0%, etc. The higher the precision, the more expensive the price.

Thermal Resistance

• The unit of ℃/W determines the heat dissipation performance of the component.

Package Size

• It affects layout and installation and can be connected in parallel with heat sinks or PCB copper foil.

Selection Guide for Metal Alloy Shunt Resistors

Clarify the range of the measured current:

• Example: The maximum current of the system is 200 A → the recommended resistance value is 0.5 mΩ (voltage drop 0.1 V), and the power P=I²R≈20 W → Select 30 W of rated power.

Determine the requirements for accuracy and temperature coefficient:

• Precision instruments → ±0.1%, TCR ≤ ±20 ppm/℃;
• General industrial → ±0.5%, TCR ≤ ±50 ppm/℃.

Select the alloy type and packaging form:

• High temperature or high power → CuCr foil type or bolt type;
• Precision low current → NiCr thin-film type.

Consider installation and heat dissipation requirements:

• Limit PCB space → thin-film surface mount
• High-current busbar → bolt-type parallel heat sink.

Verification of certification and reliability:

• Comply with EC-Q200 (automotive grade), UL or IEC standards;
• Consult the manufacturer's life test report.

Typical application scenarios

• Electric vehicle (EV) battery management system (BMS): Real-time monitoring of charging and discharging currents to ensure safety and balance. 
• Industrial Automation and Robotics: Current feedback of servo drive motors, precise control of torque and speed. 
• Power Inverter and UPS: Detects DC and AC currents, achieving overcurrent protection and efficiency optimization. 
• Consumer electronics: Mobile device charging management, high-end audio power amplifier current detection.

FAQ

Q1: Why is a low TCR current sensing resistor chosen?
A1: A low TCR can reduce the impact of environmental temperature changes on measurement accuracy and ensure long-term stability. 
Q2: How can the self-heating error of the shunt resistor be reduced?
A2: Increase the rated power margin, optimize the heat dissipation design, or parallel multiple small resistance values to share the power consumption. 
Q3: How to choose between bolt-type and surface-mount type current sensing resistors?
A3: Bolt-type is preferred for high current or high power consumption scenarios; surface-mount film type can be chosen for space-constrained, low-power measurement applications.