A current shunt, also known as a shunt resistor or electrical shunt, is a low-resistance component used to measure electric current. It works by creating a small voltage drop that’s directly proportional to the current flowing through it, which can then be measured with a voltmeter or microcontroller.
Current shunts are commonly used in DC circuits, power supplies, battery monitoring systems, and electronic load testing.
Table of Contents
- Why Use a Shunt Resistor to Measure Current?
- How Does a Current Shunt Work?
- DC Current Shunt Applications
- Shunt Resistor Types
- How to Measure Current with a Shunt Resistor
- Things to Watch Out For with a Current Shunt
- Summary
Why Use a Shunt Resistor to Measure Current?
Measuring current directly can be tricky, especially in high-current applications. A shunt resistor offers a simple, accurate, and safe method to monitor current without interfering significantly with the circuit.
Benefits of using a current shunt:
- Accurate current measurements
- Cost-effective and simple design
- Compatible with digital monitoring systems
- Widely used in industrial and automotive systems
How Does a Current Shunt Work?
At its core, a current shunt works on Ohm’s Law (V = I × R). When current flows through the low resistance of the shunt, it generates a small but measurable voltage drop.
Current Shunt Step-by-Step Breakdown
- The shunt resistor is placed in series with the load.
- Current flowing through the load also flows through the shunt.
- A voltage drop develops across the shunt resistor.
- This voltage is measured and used to calculate the current using Ohm’s Law.
Current Shunt Circuit Example
The following circuit is an example of how a current shunt is used. A current shunt resistor is placed in series with the load. As a result, current flows through this resistor to the load. This causes a small voltage drop across the low resistance shunt resistor, which is measured by the DC voltmeter.
Example Current Shunt Calculation
If a shunt resistor has a resistance of 0.01 ohms and you measure a voltage drop of 0.1V across it, then:
I = V / R = 0.1V / 0.01Ω = 10A
That means 10 amps of current is flowing through the circuit.
DC Current Shunt Applications
DC current shunts are particularly useful for:
- Battery monitoring in solar and UPS systems
- Electric vehicle power systems
- Motor controllers
- DC power supplies and testers
They’re usually large and robust, designed to handle high current levels with precision.
Shunt Resistor Types
There are a few types of electrical shunts depending on the application:
1. Low-Value Wire-Wound Resistors
Used in general-purpose applications with modest current ranges.
2. Precision Manganin Shunts
These use a metal alloy with low temperature coefficient for high accuracy in industrial systems.
3. Bus Bar Shunts
Heavy-duty shunts used in automotive or marine applications, typically in the hundreds of amps range.
How to Measure Current with a Shunt Resistor
To measure current using a shunt:
Tools You’ll Need
- A shunt resistor rated for your expected current
- A voltmeter or microcontroller ADC input (Analog-to-Digital Converter)
Steps
- Connect the shunt in series with the load (not parallel).
- Connect your voltmeter or ADC across the shunt’s terminals.
- Record the voltage.
- Use the formula
I = V / Rto calculate current.
Tip: Many current monitoring ICs and modules already have built-in shunt resistors and signal amplification.
Things to Watch Out For with a Current Shunt
- Power Dissipation: Since power = I² × R, a high current through a small resistor can still generate heat.
- Shunt Placement: Always connect the shunt on the low side (ground side) of the circuit unless you use differential measurement.
- Accuracy: Choose a shunt with a low temperature coefficient for more consistent readings.
Summary
A current shunt is a fundamental and reliable way to measure current in an electrical system. Whether you’re building a small electronics project or designing a power monitoring system, understanding how a current shunt works can take your electronics skills to the next level.
By learning how to measure current with a shunt resistor, you’ll gain hands-on insights into how real-world circuits function—making this a valuable tool in your electronics toolkit.
Check out our components category to learn more about components used in electronics.