How does TC work and what is the Temperature Coefficient of Resistance?
Temperature Control works by monitoring changes in resistance in the coil and using this to estimate temperature changes. It works because resistance increases linearly and predictably with temperature, although the amount that it increases varies greatly between wires.
TC is possible only with wire that has a reasonably high Temperature Coefficient of Resistance. The Coefficient is a numerical value that indicates how much resistance will rise for a given temperature increase. When the coefficient is high resistance will increase a lot as temperature increases. When it is low, resistance does not rise or rises a very small amount.
Ni200 was chosen by Evolv as the first TC wire because it has one of the highest coefficients amongst common metals/wires. Kanthal has an extremely low coefficient - its resistance barely rises at all even with hundreds of degrees of heating.
The Coefficient of pure Nickel is 0.006. In practice this means that for every °C hotter a wire gets, its resistance rises by 0.0006Ω - which is the coefficient value divided by 10, for reasons I don't quite understand yet!
Example:
- A coil is at 0.10Ω at room temperature (20°C / 68°F)
- You vape and the chip sees its resistance is now 0.22Ω
- So it knows its resistance rose by 0.12Ω
- Then it calculates using the coefficient of 0.006 that a resistance rise of 0.12Ω equals a temperature rise of 200°C (392° F)
- And therefore the coil temperature is now 220°C (428°F)
- (0.22Ω - 0.10Ω) / (0.006 / 10) = 200°C (392°F)
- + 20°C (68°F) [starting temp] = 220°C (428°F) [coil temp]
DNA 40 and Yihi TC devices have Nickel's (or Ni200's) Coefficient hardcoded, so they only work accurately with Ni200 wire.
TC vaping with other wire is thus inaccurate by default, unless the mod allows the coefficient to be adjusted to suit the wire.
What wires besides Ni200 could we use?
At this time, there are three that I know about and I've tested two:
- Titanium (Grade 1)
- Stainless Steel (SS317L)
- Dicodes' Resistherm NiFe30
Titanium
Titanium has a coefficient of 0.0035, just over half compared to Nickel's of 0.006.
It is already being used for TC vapes (existing ECF thread:
Titanium wire, vaping and safety.) It's possible to do this on normal TC mods but to do so requires a temperature offset of around 90°F - ie. one would set 340° when one wanted 430°.
With a corrected coefficient, this will no longer necessary - the real desired temp can be set.
The advantages of Titanium over Ni200 are various, including enabling the use of contact coils (not spaced) and higher resistance ranges. It's also stronger and won't break easily like Ni200 often does. Much more info is in the above thread
Stainless Steel has a coefficient of 0.00094, less than one-sixth of Nickel's.
This means that SS can not be properly used for TC without adjusting the coefficient - its resistance increases with temperature too little for normal mods, that are expecting Ni200, to use effectively.
Some people have vaped SS on normal TC mods, and it does somewhat reduce dry hits, but it will still burn cotton. But to use it effectively, a coefficient adjustment is necessary.
Once the coefficient is adjusted, Stainless Steel works properly - no burnt cotton. However my testing thus far has still required a temperature offset, albeit not as much as people have had to do with Titanium. When using the Infinite Nickel Purity feature, I have set an offset of around 50°F when using SS.
The advantages of Stainless Steel versus Ni200 are the same as for Titanium - contact coils, higher resistance ranges, stronger. The advantages of SS versus Titanium is that it's much easier to work with - malleable, easy to coil. It is also readily available, and cheap.
The safety aspects of it are unknown at this point in time, though theoretically it should be fairly safe at TC type temperatures (perhaps safer than Ni200 even, though don't quote me on that!)
Dicodes' Resistherm NiFe30
This is a new wire that Dicods are introducing along with their new mods. Its coefficient 0.0032, very similar to Titanium.
I have ordered some for testing, and know little about it other than it's currently very expensive!
In one of their manuals, Dicodes state that it is easier to work with than Ni200 (what isn't?) I don't know how it will compare to SS and Titanium.
Infinite's implementation : Nickel Purity
What is Nickel Purity?
Nickel Purity is a setting from 10-100 that Infinite have added to their new DNA 40 clone chip. It can be found in a number of mods, including VaporFlask clones, Zero clones and VaporShark clones. These mods are available in 40, 50 and 60W variants, which are identical besides the wattage; only 60W is recommended because it is almost the same price as the lower watages.
The stated purpose of Nickel Purity is to allow users who have lower quality Ni200 wire - such as is commonly found in China - to better use TC. However, it has far more use besides that - and thus is rather poorly named.
It works by by directly modifying the Coefficient of Resistance value that the mod uses to estimate temperature increases from resistance increases in the coil wire. If nickel wire is less pure, it will have a lower coefficient - the resistance will rise less with each degree of temperature increase. The coefficient for less pure Ni200 will be lower than 0.006, perhaps 0.005 or whatever.
In fact, the feature is much more useful than its name suggests. In most of the world we do not suffer from poor Ni200. But as Infinite implemented Nickel Purity as a scale across a range of coefficient values, it has much more interesting uses.
This feature is exciting for us because allows us to use different wire altogether, including Titanium Grade 1, Stainless Steel, and the new Resistherm wire.
My testing has indicated that this works well, enabling better and easier use of Titanium without temperature offsets, and making the use of Stainless Steel properly usable for TC for the first time.
How does Nickel Purity work?
My testing indicates that it works very well, and very logically.
It would appear to quite simply be a Temperature Coefficient of Resistance scale.
The scale of Nickel Purity is 10 - 100. The default on the new Infinite mods is 70.
My testing has indicated that a value of 10 is roughly equivalent to a coefficient value of 0.001 and a value of 100 is 0.01.
- Ni200's coefficient of approx. 0.006 would suggest a value of 60.
- Titanium's coefficient of 0.0035 would suggest 35.
- And Stainless Steel, whose coefficient is around 0.00094, would use a value of 10.
I have tested all these wires and various values, and found that they mostly work as expected:
- Titanium on a setting of 35 vapes well, and much better than it does on a normal TC mod (DNA 40/Yihi).
- However I have found a slightly better vape from increasing the value, up to around 42.
- Stainless Steel on a setting of 10 also vapes well, and becomes properly usable for TC for the first time
- But a temperature offset is still required - around 40-50°F I am finding.
- I still need to do more thorough testing, including with other attys
- With Ni200, a value of 60 would seem appropriate from the scale, but in practice I am finding the default of 70 works a bit better (no doubt that's why it's the default)
I still need to do more testing to understand these results fully. It did seem from my first testing that the scale was fairly linear with coefficient, but in practice I am finding that I want to set the value a little higher than suggested by that correlation.
I am in the process of doing further testing and will update as I find more.
But the great news is that it definitely works, making vaping on Ti much easier and more convenient, and enabling proper TC use of Stainless Steel for the first time.
How to test Nickel Purity settings?
The new Infinite chip mods have an additional excellent feature that made it very easy to test for this. Unlike most/all standard TC mods, the Infinite chip displays live resistance readings during the vape.
So say you put on a TC coil that measures 0.10, and then you start vaping. Most TC mods will continue to show the static value of 0.10, because it hides the real resistance value of the coil.
In contrast, the Infinite shows the live updating resistance. It also shows the live updating temperature (or rather its estimate of it.)
By comparing these values together - what is the resistance, and what does it think the temperature is? - it's possible to work out what coefficient value it's using for that calculation.
The only downside is the annoying "Temperature Protection" message it often flashes, which obscures some of the data. But this can be worked around by setting a temperature too high, so the message is not flashed or flashed more rarely.
I will give more details on my testing, and data, soon.
