Shunt Resistor Inputs
Formula Used
Vm = Im × Rm
Ish = Itotal − Im
Rsh,op = Vm ÷ Ish
Rsh,ref = Rsh,op ÷ [1 + α(Top − Tref)]
P = Ish2 × Rsh,op
R = ρL ÷ A, therefore A = ρL ÷ R
These formulas model a classic current-divider shunt. The meter and shunt share the same voltage, while most current bypasses the sensitive meter movement.
How to Use This Calculator
- Enter the target full-scale current you want to measure.
- Enter the meter movement full-scale current and its internal resistance.
- Select a shunt material, or choose custom values for resistivity and temperature coefficient.
- Set reference and operating temperature to account for thermal drift.
- Optionally enter strip length, width, and thickness for physical sizing checks.
- Choose a power safety factor for a more realistic wattage recommendation.
- Press the calculate button to view the shunt value, power loss, sizing guidance, and graph.
- Use the CSV and PDF buttons to export the final design summary.
Example Data Table
| Case | Total Current | Meter Current | Meter Resistance | Burden Voltage | Approx. Shunt | Power |
|---|---|---|---|---|---|---|
| Panel meter extension | 10 A | 1 mA | 50 Ω | 50 mV | 5.0005 mΩ | 0.49995 W |
| Battery monitor | 50 A | 1 mA | 50 Ω | 50 mV | 1.0000 mΩ | 2.49995 W |
| High-current bench shunt | 100 A | 1 mA | 75 Ω | 75 mV | 0.7500 mΩ | 7.49993 W |
These sample rows illustrate typical 50 mV and 75 mV shunt-style designs used in instrumentation and power systems.
Frequently Asked Questions
1) What does a shunt resistor do?
A shunt resistor bypasses most of the circuit current around a sensitive meter or sensing input. It creates a small known voltage drop that lets the instrument infer the total current safely.
2) Why is burden voltage important?
Burden voltage is the voltage lost across the shunt and meter network. Lower burden reduces measurement disturbance, which matters in batteries, power rails, and low-voltage systems.
3) Why do low temperature-coefficient materials matter?
Low-drift alloys such as manganin and constantan keep resistance more stable over temperature. That improves current accuracy when the shunt heats up during continuous or heavy-load operation.
4) How do I choose the power rating?
Start with calculated full-scale power, then multiply by a safety factor. Select the next practical rating above that result to improve reliability and thermal headroom.
5) Can I use copper as the shunt material?
You can, but copper has a high temperature coefficient. Its resistance changes much more with temperature, so it is less stable for precision current measurement than dedicated shunt alloys.
6) Why does the calculator ask for strip geometry?
Length, width, and thickness help convert electrical resistance targets into practical dimensions. That makes the tool useful both for circuit design and for physical shunt strip sizing.
7) Is the meter current always tiny compared with total current?
Usually yes. In most shunt-based ammeters, the meter path carries only a small fraction of the total current, while the shunt carries almost everything else.
8) Does this replace thermal testing?
No. This tool provides design estimates. Final products still need thermal validation, tolerance checks, mounting review, and real load testing before production use.