Calculator KB-36
Shunt calculator
The basis of every ammeter and overload protection circuit.
Result
In brief: Current shunt calculator: resistance for a given current and a voltage drop of 50, 75, or 100 mV, power dissipation, and wire length for manganin, constantan, or copper. Example: Shunt resistance: 0.75 mΩ.
Calculation example
| Maximum current | 100 A |
|---|---|
| Shunt voltage drop | 75 mV |
| Material | Manganin |
| Wire diameter | 2 mm |
| Shunt resistance | 0.75 mΩ |
|---|---|
| Power dissipated | 7.5 W |
| Minimum power rating | 15 W |
| Wire length | 5.48 mm |
How it is calculated
P = U · I
L = R · S / ρ
Connect the shunt in series with the load, then measure the voltage across it with a meter or amplifier. A lower voltage drop saves power but requires a more sensitive meter.
What to look for
- Connect the sense leads directly to the shunt body, separately from the power leads. This is a four-wire connection.
- Manganin's resistance barely changes as it heats up, which is why factory-made shunts are made from it.
Frequently asked questions
What is the resistance of a 100 A, 75 mV shunt?
R = U / I = 0.075 / 100 = 0.75 mΩ. At full current, the shunt dissipates 7.5 W.
How can I make a shunt myself?
Use manganin or constantan: their resistance changes very little with temperature. For 0.75 mΩ, you need only about 5.5 mm of 2 mm diameter manganin wire, so in practice, use thinner wire or several strands in parallel.
Why connect a shunt with four wires?
So the resistance of the contacts and power leads doesn't affect the measurement: at fractions of a milliohm, it's comparable to the shunt's own resistance.
