How to calculate the shunt

How to calculate the shunt

The shunt serves in order that take away the main current in a chain from some of its site. For this purpose he joins parallel to this site. As a rule, it is the conductor with a small resistance calculated on passing of current of a certain size. For calculation of the shunt it is necessary to know what current on it has to proceed.

It is required to you

  • — ampermeter;
  • — tester;
  • — conductor of the known section from the known material;
  • — table of specific resistance.


1. Attach the shunt parallel to the ampermeter to expand possibilities of its measurement. In this case through the shunt there passes the main current, and that its part which is subject to measurement, passes through the ampermeter. Calculate rated current in network by a special formula.

2. To calculate the shunt, learn the maximum current which to measure device is necessary. For this purpose measure tension on U current source in volts and divide it into the general resistance of a chain of R in Ohms. You perform all measurements a tester if a direct current at the same time consider polarity of the device. Find rated current in a chain, having divided tension into resistance of I=U/R. Examine a scale of the ampermeter and learn the maximum current which they can measure.

3. Find shunt resistance. For this purpose measure own resistance of the R1 ampermeter in Ohms, and find the necessary resistance of the shunt, having divided the work of the maximum current which can be measured by the I1 device and its resistance R1 on rated current in network I (R=(I1∙R1) / I).

4. Example. It is necessary to measure current in a chain where the maximum value can reach 20 A. It is for this purpose offered to use the ampermeter with the maximum possible current of measurement 100 ma and resistance of 200 Ohms. Shunt resistance in this case will be R= (0.1∙200)/20 = 1 Ohm.

5. As shunts use standard resistors. If those are not available, manufacture the shunt. For production of shunts it is the best of all to take conductors from copper or other material with high conductivity. To calculate the necessary length of the conductor of shunt l, take a wire of the known section S and learn the specific resistance of material ρ of which this adaptation is manufactured. Then, R resistance, increase by the section of the conductor measured in mm², and divide into its specific resistance expressed in Ohm ∙ to mm²/м, taken from the special table l=R∙S/ρ.

6. To manufacture the shunt for the ampermeter of the example from a copper wire with a section of 0.2 mm given above², take its length which calculate by m formula l=1∙0.2/0.0175=11.43. Use the same principle also when shunting any other site of a chain.

Author: «MirrorInfo» Dream Team