Current. Too piffling of it, and you can't get where you're going, too much and your hardware'due south on fire. In many projects, information technology's desirable to know merely how much current is beingness drawn, and fifty-fifty more desirable to limit it to avoid catastrophic destruction. The humble current shunt is an excellent style to exercise just that.

Ohm's Law.

To sympathise current, information technology'due south important to sympathise Ohm'due south Police force, which defines the relationship between current, voltage, and resistance. If we know two out of the 3, nosotros can calculate the unknown. This is the underlying principle behind the electric current shunt. A current flows through a resistor, and the voltage drop beyond the resistor is measured. If the resistance likewise is known, the electric current tin be calculated with the equation I=V/R.

This elementary fact tin can be used to great effect. Equally an example, consider a microcontroller used to command a DC motor with a transistor controlled by a PWM output. A known resistance is placed inline with the motor and, the voltage drop across information technology measured with the onboard analog-to-digital converter. With a few lines of code, it's simple for the microcontroller to calculate the current flowing to the motor. Armed with this knowledge, lawmaking can be crafted to limit the motor current draw for such purposes as avoiding overheating the motor, or to protect the drive transistors from failure.

In fact, such strategies can exist used in a broad variety of applications. In microcontroller projects you lot can measure as many currents equally you accept spare ADC channels and time. Whether you're driving loftier power LEDs or trying to build protection into a power supply, current shunts are key to doing this.

Resistors come in all shapes and sizes!

With the theoretical side of things covered, information technology'south hither that we veer towards the practical. If you're new to electronics, when y'all hear "resistor", yous're probably thinking of a little 1/4 watt beige device with some colourful bands indicating the value. Yet resistors come in all shapes and sizes. In fact, everything except superconducting materials have resistance – fifty-fifty just blank wire! So when you're choosing a resistor to use every bit a current shunt, where should you start? The get-go thing to think is that power loss is relative to resistance.

The ability lost in the resistor is equal to the electric current squared, multiplied by the resistance. P = IV = I^2R = V^2/R. A high resistance will limit the current that can pass through the circuit, and also waste power as heat. For these reasons, the current shunt resistance should be as depression every bit possible.

What this ways in practical terms is that in some cases, a link of wire is chosen to act equally the shunt. This is prevalent in many applications, such as motor controllers you might find on an electric skateboard or due east-bike. As long as the resistance of the wire link is known, it can be used to calculate the current passing through information technology.

A brushed motor speed controller from an electric scooter. Annotation the wire link interim as a current shunt, circled in red.

The shunt is generally used to protect the speed controller from a load drawing too much current, or to limit the speed of the attached motor. If you want to play fast and loose with such a controller and are thirsty for more speed, in that location'south a uncomplicated trick. By cut the connection from the shunt to the controller's sense line, and instead tying the sense line to ground, it volition appear as if no current is flowing since no voltage drop is measured. The speed controller will reply by giving all the power information technology tin, which usually ends in flames as the transistors in the controller fail nether excessive load.

Current shunts designed for taking authentic measurements in the tens of amps.

Other times, a very authentic current shunt may be desired during the demote testing of equipment. In this case, a precision current shunt may be used with a voltmeter to determine the current passing through the circuit. Typical shunts are generally rated to have a voltage drop of 50 mV at their rated current. Armed with a suitably sensitive voltmeter, it's possible to mensurate large currents relatively safely – something not doable with the boilerplate multimeter.

These are just a handful of means current shunts can be used. Fundamentally, proper electric current measurement can make a wide variety of projects safer, more robust, and more than reliable. The primal is applying the basic principle of the current shunt with the right hardware for your application, which will ensure that any measurements taken are reliable and safe.