ART
BEAUTY & WELLNESS
CRAFT
CULTURE & HISTORY
ENTERTAINMENT
ENVIRONMENT
FOOD & DRINKS
REVERSE ENGINEERING
SCIENCES
SPORTS
TECHNOLOGY
WEARABLES
Constantan Resistance Wire from Copper and Nickel
Besserwisser16 (Wikimedia Commons) · CC0
Forge

Created by

Forge

13. October 2026NO
2
0
0
0
0

Constantan Resistance Wire from Copper and Nickel

Constantan is a copper-nickel alloy, usually 55 % copper and 45 % nickel, whose electrical resistance stays nearly the same as it warms; that is why strain gauges, thermocouples and resistance coils are wound with it. Copper and nickel melt together in any proportion, so the alloy is made by fusing the two, casting small sticks and drawing them into wire. The melt follows C. Morfit's copper-nickel alloy as Brannt gives it in *The Metallic Alloys* (1889): nickel and an equal weight of copper fused with borax in a graphite crucible, the rest of the copper stirred in. Hiorns (1912) adds that the nickel must be as pure as possible, which is what the Mond process gives.
Advanced
Foundry day, then drawing

Instructions

1

Weigh the charge

For 1 kg of 55/45 constantan weigh 450 g nickel and 550 g copper, and set aside 100 g of the copper for the second addition. Use nickel as pure as you can get: Hiorns warns that silicon, carbon, iron and sulphur in it greatly reduce how well the alloy works.

Materials for this step:

Copper IngotCopper Ingot550 g
Carbonyl NickelCarbonyl Nickel450 g

Tools needed:

Balance ScaleBalance Scale
2

Fuse nickel with an equal weight of copper

Put the nickel and an equal weight of copper (450 g of each) into a graphite crucible with some borax, and fuse them in the furnace. This is Morfit's first stage: nickel melts far hotter than copper, and melting it among copper brings it down sooner. Constantan itself melts at about 1,220–1,300 °C.

Materials for this step:

Borax PowderBorax Powder1 as required

Tools needed:

Graphite-Clay CrucibleGraphite-Clay Crucible
Charcoal FurnaceCharcoal Furnace
Crucible TongsCrucible Tongs
Heat-Resistant GlovesHeat-Resistant Gloves
Leather ApronLeather Apron
3

Stir in the rest of the copper

Add the remaining 100 g of copper to the melted mass, stirring constantly with an iron rod until it has gone in and the metal is one even liquid.

Tools needed:

Iron StirrerIron Stirrer
Charcoal FurnaceCharcoal Furnace
Crucible TongsCrucible Tongs
Heat-Resistant GlovesHeat-Resistant Gloves
4

Cast small sticks

Pour the alloy into a warmed ingot mould as small sticks, as Morfit did. Pour in one run; the alloy chills quickly.

Tools needed:

Ingot MouldIngot Mould
Crucible TongsCrucible Tongs
Heat-Resistant GlovesHeat-Resistant Gloves
Leather ApronLeather Apron
5

Anneal the sticks

Anneal the cast sticks before working them: cast copper-nickel is crystalline, and Hiorns gives careful annealing at a moderate temperature as the cure.

Tools needed:

Annealing OvenAnnealing Oven
Crucible TongsCrucible Tongs
Heat-Resistant GlovesHeat-Resistant Gloves
6

Draw it like copper wire

Forge a stick into a round rod, file a taper and draw it through the drawplate hole by hole, as copper wire is drawn. Never take the size down too fast: Hiorns warns that metal drawn without annealing breaks unless it rests five to ten minutes between passes. Anneal it as the copper wire is annealed. Simmons's strain gauges used No. 40 gauge, about 0.08 mm.
7

Measure the resistance

Measure the diameter in several places, cut a measured length and find its resistance on a Wheatstone bridge. Compare the result with the ohms per metre in the next step. A wire that reads much higher than expected has a thin place or a crack in it.

Tools needed:

MicrometerMicrometer
Wheatstone BridgeWheatstone Bridge
8

Charge and resistance figures

Loading Jupyter Notebook...
9

Troubleshooting

Constantan wire troubleshooting.

Flow

Loading...
10

History and honest limits

In 1887 Edward Weston found an alloy whose resistance falls as it warms, a property, he wrote, of no other metallic conductor he knew. Wikipedia says his "Alloy No. 2" was produced in Germany and renamed Konstantan. By 1912 Hiorns listed Constantan, Eureka and Heckenham metal among the copper-nickel alloys used for resistances. Morfit's alloy was 33 nickel to 67 copper; we keep his two-stage method and scale it to 55/45, the usual constantan and Simmons's wire. That scaling is ours. The 55/45 figure and the resistivity are from Wikipedia's Constantan article. Very fine wire like No. 40 gauge needs drawplate holes that fine.

Materials

3

Tools Required

11

This blueprint makes

Thumbnail
Placeholder

Constantan Wire

Free

4
0
1

Related Blueprints

These blueprints share knowledge with this one — techniques, materials, or principles that connect them in the learning graph.

Carbonyl Nickel by the Mond Process: Mond, 1891
Hazardous

Carbonyl Nickel by the Mond Process: Mond, 1891

by PeterSE

Metalworking

3
0
0
0
0
0

CC0 Public Domain

This blueprint is released under CC0. You are free to copy, modify, distribute, and use this work for any purpose, without asking permission.

Support the Maker by purchasing products through their Blueprint where they earn a Maker Commission set by Vendors, or create a new iteration of this Blueprint and include it as a connection in your own Blueprint to share revenue.

Discussion

(0)

Log in to join the discussion

Loading comments...