TC Accuracy and Coil Resistance

[m1ke]

I'm having a great and very consistent experience with TC using iSub 0.5Ω SS316L BVCs on a Pico (in default SS mode). After reading a lot of people's experiences with TC, I'm starting to think that a 0.5Ω coil will be more accurate than 0.1Ω coil.

Basically, is it true to say that higher resistance sub-ohm coils make for a more consistent and accurate TC experience?

 

[Jim_ MDP]

I'm having a great and very consistent experience with TC using iSub 0.5Ω SS316L BVCs on a Pico (in default SS mode). After reading a lot of people's experiences with TC, I'm starting to think that a 0.5Ω coil will be more accurate than 0.1Ω coil.

Basically, is it true to say that higher resistance sub-ohm coils make for a more consistent and accurate TC experience?

Yes... the amount of resistance rise per degree of temp rise is proportional to the room temp res. That's actually exactly what the TCR value represents, and higher is better.
Or at least more accurate... I'll stick to my SS over Ni and Ti though

So a higher starting point will have a (slightly) greater res rise... and that's easier for our mods to see, track and stay ahead of. In other words... a more precise TC vape.

Not too many months ago, JoyeTech (JT, Wismec & Eleaf) raised their TC res ceiling to 1.5 ohm. Different brands and different chips have their own caps though, for when you roll your own. Anywhere around 0.6 to 1.0 is quite normal unless you build something exotic or with multiple coils or cores. Easier on the mods and batteries too.

 

[m1ke]

Yes... the amount of resistance rise per degree of temp rise is proportional to the room temp res. That's actually exactly what the TCR value represents, and higher is better.
Or at least more accurate... I'll stick to my SS over Ni and Ti though

So a higher starting point will have a (slightly) greater res rise... and that's easier for our mods to see, track and stay ahead of. In other words... a more precise TC vape.

Thanks for these details. I understand why it's more accurate now.

 

[m1ke]

I think some of the negative experiences I've read about are because people are wrapping coils that have too low of a resistance.

By the way, I think the iSub V works so well with TC because what screws into the 510 connection is actually the coil thread. I don't know how many tanks are set up like that..

 

[Jim_ MDP]

That and using Stainless... it really has quite a low TCR for our purposes.
But that's the only knock against it, so I'll deal with it.

And mods are rapidly getting faster, more accurate and able to discern smaller changes (granularity) making even lower TCR wires possible.

 

[GeorgeS]

Just for means of an example, I'll make up a wire type that DOUBLES its resistance going from room temperature (70F) to a vaping temperature of 470F. The wire also does this in a LINEAR fashion and as such does not require a curve.

Given the following room temperature atomizer resistances of 0.1, 0.5 and 1.0ohm the coils at 470F would read 0.2, 1.0 and 2.0ohms.

Follow me so far?

The 'granularity' of the resistance/temp reading will be the resistance change divided by the temperature change. Hence:
0.1 / 400 = 0.00025 ohms per degree F
0.5 / 400 = 0.00125 ohms per degree F
1.0 / 400 = 0.0025 ohms per degree F

The other two factors that play into this is the parasite resistance of your mod+build (and the stability of it) and how many digits of resistance the TC chip in your mod can read.

In the real world we can reference 'SteamEngine' and the 'Wire Wizard' tab to see not only an estimated accuracy value of our builds but what the resistance change values are for real world wire types. The way I understand it, in the 'table' there is a 'resistance factor' which can be used as a multiplication factor. The values that might be useful here are listed under room temperature of 68F and 392F. (room temperature is seemingly always "1.0".

SS317L = 1.1692
SS430 = 1.2484
Ti-01 = 1.66318
NiFe52 = 1.73
Ni200 = 2.08

So given the same coil resistance of 0.2 ohms a coil wound with Ni200 would rise to 0.416 ohms at vaping (392F) temperature and the SS317L coil would rise to 0.23384 ohms.

(IMHO: a change of 0.03384 does not give your mod much to work with)

 

[Jim_ MDP]

Thank you George... the kind of detail I was too lazy to type out.