Shunt

How does a shunt works?

Short:
A shunt is a very small resistor that is used to measure current. The resistor is added in series to the load and the voltage drop is measured. From the voltage drop and the value of the resistor the current can be calculated.

In Detail:
The best way to get a better understanding is to have a look at the principle of voltage divider.

In a voltage divider the current is always the same.

-> Means we can really use a second resistor to find out the current that is flowing through the load.

Every resistor has a voltage drop that has the ratio of the resistor to the total resistance.

Or the voltage drops across the resistors must add up to the total voltage.

-> This tells us that we have to choose the resistor as small as possible so that we don’t drag to much voltage from the load.

This table displays how the resistance value of the shunt (R2) drains power if it is too high. Also you can see how small the voltage drop gets if the resistance is to low, what makes it hard to measure.