Constantan vs Manganin
Both are copper-nickel-ish alloys with roughly half a micro-ohm-metre of resistivity. The decision is usually made by three numbers and one workshop reality.
| Constantan (6J40) | Manganin (6J12 / 6J13) | |
|---|---|---|
| Resistivity, 20 °C | ≈ 0.49 µΩ·m | ≈ 0.43–0.47 µΩ·m |
| Temperature coefficient | ≈ ±20 ppm/K | ≈ ±10–20 ppm/K |
| Thermal EMF vs copper | Higher (it is a thermocouple leg) | Very low, 1–2 µV/K |
| Service temperature | ≈ 400 °C | ≈ 60–100 °C |
| Soldering | Easy | Possible, less forgiving |
| Relative cost | Lower | Higher |
| Thermocouple use | Negative leg of E, J, T | Not used |
How the choice is actually made
If the part carries current and sits in a warm enclosure, and the accuracy target is a percent or two, constantan wins on cost and on how easily it terminates. If the part is a reference — a standard resistor, a calibration shunt, anything where drift is the specification — manganin's lower thermal EMF and tighter coefficient win, and the price difference stops mattering.
The trap is using constantan as a measurement reference and then wondering why the reading moves when the enclosure warms. Constantan's coefficient is small, not zero, and its EMF against copper is deliberately non-zero because it is designed to work against NiCr and iron.
A third option people forget
CuNi44 sits between them: constantan-level resistivity with resistance-alloy rather than thermocouple-grade control. For load banks and braking resistors, where nobody is measuring microvolts, it is often the right buy.
Send the resistance value, the current, and the enclosure temperature. We will tell you which grade we would use — including when the answer is that you should not buy from us.
Can manganin be used above 100 °C?
Which is easier to weld?
Send the specification — diameter, grade, temper, quantity.
We come back with a confirmed lead time and the documentation we can issue for the shipment. 100 g sample at cost; orders from 1 kg.
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