The only property of the coil materials that is essential to coil building, is the resistivity of the material. All the wires in Steam Engine need to have a precise resistivity number in order for the calculator to even work.
For temperature controlled vaping, some type of data describing the relationship between temperature and resistance is also important. This can either be a single number called temperature coefficient of resistance (TCR), or it can be a more detailed multi-point curve consisting of resistivity factors at different temperatures (which I chose to abbreviate TFR, “temperature factors of resistance”, in the calculators).
Density and specific heat are the two last values, and the least important ones. They’re “nice to have” features. They will give you a heat capacity and a mass for your coil – not extremely useful, but interesting enough.
Whenever I can’t find the resistivity of a material, I simply cannot add it to the calculators. But when I have the resistivity, and perhaps the TCR or TFR data, omitting a material just because I lack density or heat capacity data, would be a shame. Luckily both these values can be estimated without any major risks.
For the NiFe30 wires, I had to do just that – until an attentive user in my Facebook group pointed me to the actual datasheet for Resistherm NiFe30! (PDF in German.)
This data allowed me to tweak the values for heat capacity and density for all the NiFe30 variants – that is, to replace the estimates with hard data.
- An estimated density of 8.2 g/cm³ was replaced with the accurate 8.5 g/cm³ for all the NiFe30 materials (except StealthVape‘s NiFe, which had the correct density all along, because they actually got this number straight from their own manufacturer and shared it with me).
- An estimated specific heat of 0.45 J/g×K was replaced with the more accurate 0.42 J/g×K for all types of NiFe30.
And lo and behold, the datasheet also contained a TFR curve for Resistherm. This curve seems to be a little bit steeper overall than the linear TCR that was used before.
I have updated the Resistherm NiFe30 data point with this curve, which is used instead of the single TCR from now on.