@mrmonday thanks for your PM, I was in the process of replying last night when I fell asleep. My first response was to direct you to this thread so glad you're here.
This is what I was going on to say. I think this is good for general discussion, because it raises a point I wanted to discuss with
@tchavei and other Titanium veterans:
The basic principle is that TC mods calculate the temperature by monitoring the rise in resistance of the coil. They do this with the following formula:
ΔT = ST + (Δρ / α * ρ0)
Where:
ST : Starting temperature
ΔT : Change of temperature
Δρ : Change of the resistivity
α : Temperature Coefficient of Resistance (TCR)
ρ0 : Original resistivity
The Temperature Coefficient of Resistance (TCR) is the key number. For Ni200, it's around
0.0062. For Titanium, it's
0.0035.
So let's say you start with a Titanium coil reading 0.40Ω. You vape it on a normal TC mod, that is expecting Ni200. The mod sees its resistance is now 0.673Ω. It calculates the following:
ST = 20°C
p0 = 0.40Ω
Δρ = 0.673Ω - 0.40Ω = 0.273Ω (change of resistance)
α = 0.0062 (Temperature Coefficient of Resistance for Ni200)
ΔT = 20°C + 0.273 / (0.0062 * 0.40) =
130°C / 266°F
So, this mod thinks that a 0.273Ω rise on a 0.40Ω coil means that coil is now at 213°F.
But the coil is not Ni200, it's Titanium. The calculation it needed to do was as follows:
ST = 20°C
p0 = 0.40Ω
Δρ = 0.673Ω - 0.40Ω = 0.273Ω (change of resistance)
α =
0.0035 (Temperature Coefficient of Resistance for Titanium)
ΔT = 20°C + 0.273 / (
0.0035 * 0.40) =
215°C / 419°F
So this coil that started at 0.40Ω and increased to 0.673Ω has actually heated from 20°C (68°F) to 215°C (419°F).
But because the mod used Ni200's TCR it thinks it's only at 130°C / 266°F.
So setting the temp limiting on any (Ni200-expecting) TC mod to 130°C / 266°F will cause it to back off wattage when the coil is actually at 215°C / 419°F - an offset of 85°C / 153°F
However, this is noticeably different to the real-world offsets used by
@tchavei and others. They appear to be setting their TC much higher than the numbers suggest:
For me, my best vape for liquid x is 185C (365f) and for liquid y it's 180C (356f).
I don't really care that in reality the coil is being heated to 230C (446f) or 225C (437f)
So Tony is setting 185°C / 356°F when he wants 230°C / 446°F - an offset of only 45°C / 90°F.
Here's what happens when I put this offset into
the TCR calculator.
In the following outputs, values I enter are
in bold; values returned by the calc are
in red.
TCR, for Ni200:
0.0062
Starting resistance (for an example Ti coil):
0.40Ω
Original temperature:
20°C
Final temperature:
185°C
Ending resistance:
0.8092Ω
TCR, for Titanium:
0.0035
Starting resistance (for an example Ti coil):
0.40Ω
Original temperature:
20°C
Final temperature:
230°C
Ending resistance:
0.694Ω
In other words: The mod is expecting a coil of 0.40Ω to rise to a resistance of
0.8092Ω for the configured temperature of 185°C.
However, a 0.40Ω Titanium coil will reach the
desired target temp (230°C) at a resistance of only
0.694Ω.
What temperature is that Titanium coil when it actually reaches
0.8092Ω?
TCR, for Titanium:
0.0035
Starting resistance (for an example Ti coil):
0.40Ω
Original temperature:
20°C
Final temperature:
312.28 °C
Ending resistance:
0.8092Ω
What setting, according to the calc, would be the right temp setting for a Ni200 TC mod when using TC?
TCR, for Ni200:
0.0062
Starting resistance (for an example Ti coil):
0.40Ω
Original temperature:
20°C
Final temperature:
138.54 °C (281 °F)
Ending resistance:
0.694Ω
Therefore, based purely on the numbers, if you want to reach a target temp of 230 °C / 446 °F with Titanium, you should set your normal Ni200 TC mod to 138.54 °C / 281 °F.
But now I cannot immediately reconcile this with the actual practices and experiences of people like
@tchavei - they appear to be setting the temp far too high, but are also getting a good experience.
@tchavei you must have done dry burn cotton tests with your offsets? A cotton burn test with the mod set to 330°F (90°F offset from 420°F)?
I don't think I've messed up the calcs as I've been doing them regularly for a week now - though it's still possible I've missed something. What's more possible is that there's more to it than just calculating the final resistance at the target temperature.
Or maybe most Ni200 mods are not using 0.0062 as their TCR (the figure of 0.0062 comes from Dicodes, who recommend it as the value for Ni200; other sources quote 0.006 for pure Nickel.)
If for example most TC mods use 0.005 as the TCR - which I have seen listed one place as the TCR for Ni200, but only one - then the correct temp for 230°C / 446°F would be 166°C / 330°F - still lower than Tony has, but close enough to the ballpark to not really notice.
Of course another possibility is just that, as the Titanium veterans set their offset by experimentation, they might have found a value that works in general usage but is not the most accurate - though if they have done dry burn cotton tests, as surely they must have, it's surprising if those higher settings are not burning cotton.
So maybe it really is that the TCR used by most current TC mods is lower than Dicodes say it should be.
I was planning to put out a new version of my
Nickel Purity / Static Resistance calculator specifically for giving the right temperature to use when vaping Titanium (or Resistherm NiFe30) on a Ni200 TC mod.
But there's no point doing that until I know if the figures are real-world usable.
I will do some tests myself today, cotton dry burn tests, but I'd love to hear the thoughts and findings of
@tchavei and other TC Titanium veterans!
