Temperature Control A Different Way?

[edyle]

So here's two crack-pot ideas I just had. I haven't crunched the numbers or considered how to do a full implementation of it either. Now as we all know the changes in resistance of nichrome or kanthal wire are very small even at high temperatures.

So run with me, come up with a way to refute these, or come up with other ones?

Both operate under the assumption that we know the resistance of the coil at rest. Which is easy to obtain and almost all regulated devices are doing this already.

Here's the real crack pot idea...
1) Say we put a hall effect sensor underneath (or as a ring around) the atomizer to measure the magnetic field of the coil. Keep in mind, these coils we're using are basically solenoids. The magnetic flux would be proportional (probably not linearly hahaha) to the temperature of the coil and could be used to cross of the variables relating to how much power is being sent to the coil verses how much is flying through (IE: creating a magnetic field). Knowing the power being supplied to the coil would help a good deal as well.

I used a little app on my cellphone which serves as a crude magnetometer, and when I fire my atomizer at 15 watts I get a shift of about 4 microtesla being about half a cm from the atomizer. I imagine the field change could be as drastic as 10microtesla and read to two decimals of accuracy under better conditions.

2) Say the user selects what gauge wire to use from a menu for Kanthal (standard material right?). The chip can quickly calculate approximately how many wraps there are at rest, or even ask if it's unsure "2.5mm 7 wraps?" (IE Steam calculator). Why couldn't a mod interpolate the temperature of the coil from the power applied over time? Sure it wouldn't be perfect and values would have to be stored under certain conditions. Imperfect coils with super long leads could create hot-spots as well. Even if it didn't give the supposed +/-1 degree accuracy which nickel wire can, isn't +/-5 degrees "good enough" to prevent whick from charring when dry?

I'm not a fan of drilling through atomizers to put IR thermometers in place or whatever, seems finicky.

1: since the magnetic field is just going to be a function of the current, measuring the magnetic field won't help; the mod already knows enough to figure out the current anyway.

2: Being able tell the mod what wire gauge etc could be usefull for the mod to make a best guess / recommended operation / vape profile.

 

[TheJester]

McClintock - Yea the magnetic field is proportional to the current. I was also hoping that some dithering in the field might occur as the wire's temperature approached the curie point. Then again the curie point is 400*C above a nice temperature setting, so probably not. I was just trying to think of a way we might be able to get more digits out of the measurement to actually interpolate temperature values. Kanthal does vary with resistance at a given temperature, just not very appreciably. So a more sensitive measurement might be able to pick up on that?

Dampmaskin - Awe man, don't kirchoff loop rule me . You're right though. I was saying, that even if kanthal was an infinite resistor, which had been implied (I think) previously in the thread IE: "20w on the mod setting -> 20w of heat leaves the coil". I just didn't want to revisit that argument. Clearly, this principle is why mech mods can be dangerous. I was thinking in current because I was trying to work out how to set up this simulation ...



I think we're on the same page. The reference I was talking about with kanthal being not 100% efficient was probably misconstrued. I tried to say that efficiency of kanthal chucking power into heat may be nearly 100% but heat moves, so what is the efficiency of the actual coil,wick, etc. As in I was more-so asking, what is the system's over-all efficiency. The reference was in the case of a furnace heated by kanthal is pg 88 of "The Kanthal Super Heating Electric Handbook" (cc) Kanthal AB - http://mtixtl.com/machineflyer/Handbook.pdf . That's why I was saying, well what is efficiency anyways. Efficiency doesn't matter too much anyways for what I'm trying to figure out.

 

[TheJester]

I'm almost tempted to do a calorimetric type test of the DNA40 temperature setting to see if it is what it says it is. I'm wondering if the majority of what it does is in the PID control. One tiny fluctuation and it can operate very poorly. If that's the case

I just realized that sensing the magnetic field really isn't that good if it comes down to a few microtesla. Move too close to a speaker or a power supply, and zoop you're 400*C over the interpolated value. I'm a chemist, so I have a tendancy to only focus on the "system" rather then the "universe", it's a common problem hahaha.

New idea -
How about this. A mod that has a divided center post which puts a strip of nickel wire through each coil? That's easier. Then again what's the difference between that and a thermistor/thermocouple anyways? hahahaha (please don't argue with me about the semantics of the exact bimetallic nature of a thermistor you know what I meant). So it could use nickel wire, but you could heat kanthal. That's not completely asinine I promise.

Now I'm being facetious. Okay I admit defeat for now, but I want to stir up some ideas and get some technical discussions about mods. Sometimes fruitful things come from such banter .

 

[Dampmaskin]

Ok, I had a quick look at the PDF, and I think we can say that the furnace efficiency is analogous to the efficiency of the regulating circuit in the mod. With most mods, that is around 90%, give or take.

The coil is 100% efficient when viewed in isolation, but looking at the mod/atomizer system as a whole, that's another story of course.

When you're designing a regulating circuit, I think it will be possible to calculate the efficiency for your specific regulator very accurately.

Regarding the heat loss of the atomizer, I think the air cooling (from taking a draw) together with the heat loss from vaporization (the phase change of the liquid) stands for the largest and most variable heat loss. Actually, I think it's so large and so variable that trying to model or approximate it would be fruitless, unless you're also measuring the speed/volume of the air, and the mass of the e-juice passing through the system.

But now it's well past bedtime in these parts of the world, so I'll bow out for now. See you around.

 

[TheJester]

Goodnight Dampmaskin thanks for helping me think some of these ideas through!

You're right, that knocks #2 off the list, and everyone had me concede that #1 won't work either. Hmmm back do the drawing board!