What Is a Shunt Resistor?
A shunt resistor is a component used to measure current in an electrical circuit.
The term “shunt” implies meanings such as “diverting” or “sidetracking,” leading to its alternative name, “current shunt.” This component is primarily used for current verification, battery level detection, and similar applications. It offers a reliable method for measuring electric current.
As current passes through the shunt resistor, its resistance value and the voltage drop across it are used to accurately determine the current. A notable feature of shunt resistors is their applicability in high-current situations.
In high-current circuits, where wires are often thick, traditional clamp-type current measurement methods can be challenging. Using a low-resistance shunt resistor, accurate and reliable current readings can be obtained. However, in high-current circuits, shunt resistors may generate significant heat, necessitating cooling solutions.
Uses of Shunt Resistors
Shunt resistors are utilized in various electrical circuit applications, as outlined below:
1. Instrumentation Wiring
Commonly, shunt resistors have a resistance value of 250Ω. The DC4-20mA current signal is a standard analog output signal, less affected by a voltage drop due to its nature as a current signal, hence its widespread use.
Conversely, DC1-5V voltage signals are often used as input signals. To convert a DC4-20mA signal to a DC1-5V voltage signal, a 250Ω resistor is connected in parallel to the input terminal.
2. Power Electronics
In power electronic devices like inverters, current control and monitoring are essential. Shunt resistors are used for controlling and detecting overcurrent. In inverters, they manage the current on the DC side and regulate the output on the AC side.
Also, in industrial rectifiers, shunt resistors are commonly used for current measurement. These rectifiers supply direct current to trains, electrolytic cells, plating tanks, etc., where currents can reach tens of thousands of amperes. Shunt resistors capable of handling these high currents are therefore essential.
3. Electric Vehicles
In electric vehicles, shunt resistors are used for current control, regulating power flow from the battery to the motor and limiting current during rapid charging to protect the battery.
Principle of Shunt Resistors
The fundamental principle of shunt resistors is based on Ohm’s Law, which states that the current (I) flowing through a resistor is proportional to the voltage (V) across it divided by its resistance (R).
Shunt resistors are typically connected in series with the circuit carrying the current to be measured. The same current flows through the shunt resistor. With its known resistance, the current can be calculated by measuring the voltage drop across it with instruments like a voltmeter.
Types of Shunt Resistors
There are various types of shunt resistors, including:
1. Wire Type Shunt Resistor
This common type uses a high-resistance metal wire, thin and wound into a coil, to achieve low resistance. It is versatile and suitable for a wide range of current values, from low to high.
2. Strip Shunt Resistor
Strip shunt resistors use a flat metal strip. Like wire-type resistors, they have low resistance and can handle high currents. They are particularly efficient in heat dissipation, enabling stable operation under high-load conditions.
3. Metal Film Shunt Resistor
Made with a metal film, these resistors involve a metal film deposited on a substrate to form the resistance pattern. Metal film shunt resistors are known for their high accuracy and stability, maintaining consistent performance even with temperature fluctuations.