# Temperature sensing mods and why kanthal won't work



## JakesSA (9/5/15)

With the rapid introduction of temperature sensing mods the question of "Will it work with Kanthal?" often pops up. The coils for temperature sensing are made of nickel and presents certain .. challenges .. to coil makers so it is a valid question indeed.

It's all got to do with a magic little number attached to each metal and alloy called "temperature coefficient of resistance". Now this is just the shortest way of saying, what change of resistance can be expected at a given temperature.

Temperature sensing mods rely on the fact that the resistance of the coil will change when it heats up, the little micro controller in the mod constantly measures the resistance in the coil and armed with this figure calculates the temperature of the coil and then applies more or less power to get to the target figure as selected by the mod owner.

So this is all fine and well and most of this info is already known to those into the arcane art of nickel coil building. It has also become rather obvious that the micro controllers will have to read much finer changes in resistance to accurately determine the coil temperature on Kanthal, but how much finer?

Here is a list of temperature coefficients of resistance for some relevant metals:

Quoted from here
The Kanthal A1 figure I found elsewhere which states it as 10 to the power of -6

Material Element/Alloy "alpha" per degree Celsius
==========================================================
Nickel -------- Element --------------- 0.005866
Iron ---------- Element --------------- 0.005671
Molybdenum ---- Element --------------- 0.004579
Tungsten ------ Element --------------- 0.004403
Aluminum ------ Element --------------- 0.004308
Copper -------- Element --------------- 0.004041
Silver -------- Element --------------- 0.003819
Platinum ------ Element --------------- 0.003729
Gold ---------- Element --------------- 0.003715
Zinc ---------- Element --------------- 0.003847
Kanthal A1 ------- Alloy -------------- 0.000001


Armed with these values one can now calculate what the change in resistance will be at a given temperature. I'll skip the formula and point you to a handy calculator here. Enter the coefficient value as stated above, divide it by 10, and enter 1 into the "power of" field.

So for a Nickel coil with a 0.2 Ohm coil at room temperature the resistance will be 0.41117 Ohm at 200 degrees Celsius, that's a large difference (0.21117 Ohms!) and reasonably easy to measure by the micro controller of the mod.

For Kanthal A1 with a 0.2 Ohm coil at room temperature the resistance will be 0.200036 Ohm at 200 degrees Celsius, a very small change (0.000036 Ohms!) and beyond the capabilities of the micro controller to measure accurately.

EDIT: The original calculations posted here was out by a factor of 10, method and totals now fixed.

Reactions: Like 4 | Agree 1 | Winner 3 | Informative 5


----------



## Silver (9/5/15)

Thanks for the explanation @JakesSA
Very well laid out and explained.

Despite Kanthal falling short for a temperature control application - it is still quite remarkable how well it holds its resistance despite the temperature change. And how much better it does that compared to the other metals. Gosh.


----------



## JakesSA (9/5/15)

Yeah its odd, stainless steel 304 grade is 0.0000172 so whilst higher its still not suitable for temperature sensing. It seems alloys of metals generally have this property but I cannot find a clear explanation of why this is, or rather, I am too much of a dumba$$ to understand the why. It does not seem to be strongly related to the constituent metals of the alloy, at least not as far as I can tell.

Since Kanthal is normally used for heating applications it would make sense to formulate the alloy to keep the resistance as stable as possible so as to ensure the power supplied does not have to be varied to keep it 'at temperature'.

Reactions: Like 3


----------



## Marzuq (9/5/15)

Awesome thanks for the insight @JakesSA. That's very informative and useful for anyone looking to get one of these mods


----------



## JakesSA (9/5/15)

Maybe @johan will share his opinion on what the requirements would be for a micro controller to accurately 'read' these small changes in resistance found in Kanthal. I assume it's a function of the ADC?

Reactions: Agree 1


----------



## Silver (9/5/15)

JakesSA said:


> Yeah its odd, stainless steel 304 grade is 0.0000172 so whilst higher its still not suitable for temperature sensing. It seems alloys of metals generally have this property but I cannot find a clear explanation of why this is, or rather, I am too much of a dumba$$ to understand the why. It does not seem to be strongly related to the constituent metals of the alloy, at least not as far as I can tell.
> 
> Since Kanthal is normally used for heating applications it would make sense to formulate the alloy to keep the resistance as stable as possible so as to ensure the power supplied does not have to be varied to keep it 'at temperature'.



Great point regarding Kanthal drawing a constant power for heating applications.

Its quite interesting, we used to think that mechanicals were like manual cars and VW mods were like automatics. Now VW mods seem like manuals and Temp Controlling mods seem like the automatics!

But still, if you build a coil at the right resistance, you control the power and the temp.
So my question would be that other than avoiding dry hits or burning your cottton, how would the vape on a well setup temp control rig compare say for example to my well set up Reo manual of manuals 

Not trying to get into a big debate here - i do appreciate the merits of temp control - just remarking that indirectly the experienced vaper is controlling the temperature on a mechanical from the coil resistance they choose to use. And if it works then it should continue to work. Unless i have missed something?


----------



## JakesSA (9/5/15)

As I see it, the amount of liquid has a large impact on the temperature of the coil. The temperature control mod monitors that and does not allow the coil to get hotter than the selected value when the 'wicking' ability of the build proves insufficient to maintain the desired temperature. 

So a theoretical perfect coil build that wicks well does not need temperature control. 

I wish I could build temperature sensing into my Reo to remind me to squonk!

Reactions: Thanks 1


----------



## Silver (9/5/15)

JakesSA said:


> As I see it, the amount of liquid has a large impact on the temperature of the coil. The temperature control mod monitors that and does not allow the coil to get hotter than the selected value when the 'wicking' ability of the build proves insufficient to maintain the desired temperature.
> 
> So a theoretical perfect coil build that wicks well does not need temperature control.
> 
> I wish I could build temperature sensing into my Reo to remind me to squonk!



Thanks @JakesSA - that was what i thought. So the perfect coil does not need much temperature control as long as its wicking correctly for that juice and setup. 

As for the squonk reminder, you have one already. Its a super advanced system like no other. In your brain. Works very well. When you sense the taste starts to change slightly, your thumb is sent a message automatically to squonk. Lol

Reactions: Like 1


----------



## JakesSA (9/5/15)

Problem is I am often a subconscious vaper .. that sounds wrong .. meaning I don't pay attention whilst vaping and often get rewarded with a dry hit from hell.

Reactions: Funny 1


----------



## johan (9/5/15)

JakesSA said:


> Maybe @johan will share his opinion on what the requirements would be for a micro controller to accurately 'read' these small changes in resistance found in Kanthal. I assume it's a function of the ADC?



You are correct, ADC input is used to measure voltage drop over the resistance of the Kanthal coil.


----------



## Gazzacpt (9/5/15)

@JakesSA you explained that so much more eloquently than I ever could I think this qualifies to be stickified

Reactions: Agree 1 | Thanks 1


----------



## BuzzGlo (9/5/15)

Sorry noob question

To sum up running a kanthol build on a temp mod is pointless. (DNA 40, SX - mini, ipv 4)

A smok m80 would be fine for temp control with kanthol cos its not doing true temp sensing but it ?


----------



## BuzzGlo (9/5/15)

JakesSA said:


> As I see it, the amount of liquid has a large impact on the temperature of the coil. The temperature control mod monitors that and does not allow the coil to get hotter than the selected value when the 'wicking' ability of the build proves insufficient to maintain the desired temperature.
> 
> So a theoretical perfect coil build that wicks well does not need temperature control.
> 
> I wish I could build temperature sensing into my Reo to remind me to squonk!



I thort temp sensing also allows to an even vape (so a smoother hit). 

by even I mean you fire it, hit the temp you set and it stays there as opposed standard vv/vw the vape would get hotter as one takes a longer hit. 

Even perfect wicking would suffer this potentially, a burnt hit is possible if the temp climbs too high and the rate of flow of juice isn't able to keep up.

am I understanding this correctly or do I expect too much of temp control.

Reactions: Agree 1


----------



## JakesSA (9/5/15)

You are indeed correct. 

The reason for the temperature climb however strongly correlates to the amount of juice available to "cool down" the coil. Keep in mind I am referring to the "theoretical" perfect coil/wick set up where there is always enough liquid available.


----------



## JakesSA (9/5/15)

BuzzGlo said:


> Sorry noob question
> 
> To sum up running a kanthol build on a temp mod is pointless. (DNA 40, SX - mini, ipv 4)
> 
> A smok m80 would be fine for temp control with kanthol cos its not doing true temp sensing but it ?



Not pointless, but cannot be temperature controlled placing more emphasis on good coil/wick set ups. On the other hand building good coils with nickel is harder than with kanthal because the material is so soft.


----------



## free3dom (10/5/15)

First, thanks so much for posting this @JakesSA - it goes a long way to better understand how temp sensing is being implemented and why the manufacturers make the choices they do. Very informative and helpful 



Silver said:


> But still, if you build a coil at the right resistance, you control the power and the temp.
> So my question would be that other than avoiding dry hits or burning your cottton, how would the vape on a well setup temp control rig compare say for example to my well set up Reo manual of manuals
> 
> Not trying to get into a big debate here - i do appreciate the merits of temp control - just remarking that indirectly the experienced vaper is controlling the temperature on a mechanical from the coil resistance they choose to use. And if it works then it should continue to work. Unless i have missed something?



This is a very interesting issue. Temperature control not only protects you from dry hits, it also smooths out the vape over the duration of the draw. This is why it makes sense for the devices to work in Joules mode, which is power over time. So instead of applying the full power you select for however long you fire, the devices average out the power over the duration of the draw.

What adds to the improved vape "quality" on this is the fact that the juice gets vapourized at different temperatures (especially during the ramp up) and because (as we've all experienced) juice tastes slightly differently at different power levels this gives a much "fuller" (for lack of a better word) flavour from most complex juices - the effect is noticeably less with single flavour juices. Of course this same effect can be achieved on mods that have "ramp up" profiles (such as the older smok devices where you could set these up).

But I think what really improves the overall experience (and causes the smooth experience) is the fact that the vapour never gets warmer than what you want it to be (based on your selected temp limit).

Personally, and from speaking to others who use temp control, I find that it changes the quality of vaping quite noticably (not always for the better as some juices were designed to taste a certain way, likely keeping in mind that the vape will get hotter over time). I prefer a cooler and more consistent vape, so for me temp sensing and control is a clear winner - especially as it's still improving 

I think the only way you would be able to simulate the effect on a mech (or even a VW) device would be to fire until it is hot and then pulse fire a few times after that. So for example you fire for 3 seconds, then let go the fire button for a split second, fire again for 1 second, and so on. This is essentially what the temp control does.

In the end I'd recommend you have a go on a properly setup device from someone who understands it. It would also be great to test it with a juice you know well, so that you can experience just how it affects the flavour 

It is without a doubt, at least something worth investigating

Reactions: Like 3


----------



## Silver (10/5/15)

free3dom said:


> First, thanks so much for posting this @JakesSA - it goes a long way to better understand how temp sensing is being implemented and why the manufacturers make the choices they do. Very informative and helpful
> 
> 
> 
> ...



Thanks @free3dom 
I appreciate your detailed reply and i now think ai understand it a bit better
You explained it so well!!

I think you hit the nail on the head, i need to try a well set up temperature controlled rig with one or two juices I know well. To see for myself what the difference in the vape is

Just one thing I thought of while reading your post. I assume future mixologists will come out with juices for temp controlled setups and perhaps even give recommended temp ranges for different types of experiences with their juice (different temps bringing out different flavours etc). And this should be more consistent than just a power recommendation which can lead to different temps depending on the coil, atty, wick etc.

Reactions: Like 1


----------



## free3dom (10/5/15)

Silver said:


> Thanks @free3dom
> I appreciate your detailed reply and i now think ai understand it a bit better
> You explained it so well!!
> 
> ...



The vape from a temp controlled device is definitely something that is better to experience than read about and I'd highly recommend everyone at least try it (best if done with a known juice, but even with an unknown one some aspects will still be very noticeable). Luckily VapeCon is coming up and there will be ample opportunity for those attending to give it a go 

In regards to mixing for temp control...I'm sure the more advanced mixologists are already experimenting with it, but being so new (and still evolving) I doubt it will become something they specifically target anytime soon. I think that more likely they will just start testing their juices on these devices as well to make sure that they perform as intended (and they may well discover that some juices are better that way). 

I often wonder just how varied the testing is that some juice makers perform with regards to devices, atomizers, airflow, wick, etc. - we all know how varied these setups can be

Reactions: Like 2


----------



## JakesSA (11/5/15)

By the way, it may be that some mods will 'guess' the temperature. That is, use a lookup table or calculation to approximate what the temperature might be given the current power output. 

Doing it this way will of course allow for the use of any coil material but given that it is not actually using the coil as a sensor, it cannot account for the other variables involved e.g. amount of liquid at the coil to cool it down, mass of coil material (thick wire takes longer to heat up), the "left over" heat in the coil from previous use etc. and therefore will be less accurate.

Reactions: Agree 2 | Informative 1


----------

