PTC ceramic heating elements

[Minus Sign]

Positive Thermal Coefficient Ceramics become extremely resistant above a composition-dependent threshold temperature. This behavior causes the material to act as its own thermostat, since current passes when it is cool, and does not when it is hot.

In layman's terms, PTC ceramics have a natural cutoff point where they will no longer conduct electricity if they get too hot.

Would this not remove the need for safety features like timers while still giving the same benefit? Also, they can't "overheat" as existing heating elements can, because they lose their ability to conduct heat at certain temperatures. The atomizers, in theory, would become safer, hardier, and more resistant to wearing out, with fewer required electronics for use, and thus also fewer parts that might fail over time.

These ceramics have a long life and a proven ability to act as a heating element in equipment like rear-window defrost heaters, space heaters, and hair dryers.

Biggest question is: can they get hot enough to vaporize nicotine solution before their inherent cutoff point?

 

[leaford]

How hot do they get? And how hot do you have to get to vaporize liquid nicotine?

Someone here spitballed 300-400F for our heating elements. I'm not sure how accurate that might be. One seller told me his got to 220f, but I think that's too low. You have to heat tobacco leaves to between 257f and 302f to vaporize the nicotine out. OTOH, maybe liquid form nicotine boils easier.

Cost would be another factor. Ceramics have to be manufactured, how pricey is this stuff?

Interesting idea, though. Maybe Ludo will see it and go HMMMMM.

 

[Minus Sign]

If I get too technical, quote something you don't understand and I will try to explain. I'm posting most of the info from websites I've been researching around in. A lot of it is...not too easy to translate accurately, but I'll try.

UL Recognition for PTC Heaters
Disc Style Size 0.100" to 0.750" (2.5mm to 19.1mm)
Rectangular Size Style Length: 0.100" to 2.00" (2.5mm to 50.8mm)
Width: 0.100" to 2.00" (2.5mm to 50.8mm)
Part Thickness 0.030" to 0.250" (0.76mm to 6.35mm)
Switch Temperature (Ts ) 40ºC to 180ºC
Voltage Rating (Vmax ) 12 volts to 240 volts
Resistance at 25ºC (R25 ) <100kW

Here is a link to some online info about them. That company appears to build them specifically for temp sensor apps, but they do make single sided heaters (range temperatures from 50ºC to 135ºC). Cost would be a factor. This is probably more expensive than steel wool...but they're still pretty dang cheap.

A savings standpoint can be considered, however. If you purchased PTC wafers in bulk, and no longer needed to purchase capacitors, vacuum sensors or other fragile equipment, it would probably be less expensive for a PTC ceramic atomizer than for current ones. Like I intimate, all these would require for operation would be a power source, connecting wires and an on/off switch. The ceramics would be their own cutoff/safety feature. You can try to run current through them forever, they are chemically incapable of overheating.

Spectrum makes middle line PTC ceramic. Nothing exotic really; their PTC reaches null resistance at close to 130º-40ºC

whats the conversion for f?

EDIT: nvm, i found a converter online. 180ºC is about 356F. 140ºC (still pretty good stuff) is near 284ºF; 130ºC=266ºF. 135ºC, the models for our purposes from the company I link, would be 275ºF.

So..if your friend is right about the liquid needing 220ºF to vaporize, they have more than a little breathing room. But if we need 400, then we'd end up being low even with quality PTC ceramic. But 400ºF, I believe, would be melting these steel wool atomizers into gloop. Well, maybe not gloop (steel has a melting point of around 1300ºC, and yes, I meant to type 2 zeros), but it would play havoc on the ultra thin wire/material.

In all honesty, I think those numbers are still very high. The vaporization point of water is only 100ºC. We may need near 150ºC to get nicotine out of tobacco, but once its out, do we need to get it to extraction heat levels again in our liquid versions? 220ºF is barely above boiling water temp (104.4º repeating C). I think the liquid/vaporization point for what we use is about that range. I think so because...cigarette smoke feels hotter than e-cig vapor. PG has a boiling point of 188C, nicotine 277C. I could very easily be wrong.

A simple experiment (which I will do soon) will be to boil some e-liquid on a stove top and register the heat of the liquid. I'll get back to you with hard figures after the tests are complete.

Next big question: how to build a PTC ceramic so it can be flash heated to reach those temps quickly. I'm guessing a wafer or waffle plate could do the trick? ceramics do best in a thin strip, and would be easiest to manufacture. Think like the inside of a toaster; those little wave heater lines inside if you look through to hole when you have a slice of bread in there. it doesn't take long for those strips to get red hot. A thin strip connecting the two contacts would probably be enough to do the trick with the minimum cost to manufacturers.

Keep in mind, that the original patent considers ceramics in their construction. They used piezoelectric ceramics in some of the prototypes; which do and are pretty much the same thing (note from the information that "sudden temperature fluctuations can generate relatively high voltages (in piezoelectric ceramics), capable of depolarizing the ceramic element". Those ceramics need a capacitor to regulate such temperature and voltage changes; as I understand things (which is my way of saying I could be wrong) PTC doesn't.

 

[TropicalBob]

Minus Sign, I just read that original patent. Oh my goodness, but it is thorough! E-cigs were supposed to combine a heating element AND atomisation, and the liquid was to be injected by a pump, not leaked from a polyester filter. What we have on the market now is the result of cheapening what looks to be vastly superior, but more expensive products.

I haven't studied those engineering drawings in detail, but those are not what we use. Those drawings are what the Ruyan inventor patented in 2004. My burning question now is why don't we have those ultrasonic misters with liquid reservoirs and pressure injection, etc, etc. If Ruyan made one of those, it would be worth the necessarily higher price!

BTW: For the technically minded, the patent is at http://www.esigaretshop.nl/images/patent.pdf

 

[Minus Sign]

I haven't studied those engineering drawings in detail, but those are not what we use. Those drawings are what the Ruyan inventor patented in 2004. My burning question now is why don't we have those ultrasonic misters with liquid reservoirs and pressure injection, etc, etc.

That is a really good question TB. Possible answers range from manufacturing cheaper designs first to maximize startup cost/return revenue, to a simple desire to keep the market inundated with progressively better models to keep consumers upgrading to even the possibility that original, more expensive prototypes proved less effective at their desired task.

I'm not going to take a public stance on any of these speculations, or the varying shades of gray between each, but to say that I hope Janty's next "revolution" they mention and compare to the "Guitar Hero" principle in their second post of the thread will include improved atomizer elements. If not PTC ceramics, then something that can hold up for a while.

I have to get a special thermometer to reach the temperatures needed to stovetop test vaporization point for our liquids. I'll update with results when I can.