Coil heating from the middle - a technical question

Hello there!

First things first, I have a practical question about my Ti01 coil builds. I’m not very experienced with TC, just recently in the last month or two have I succeeded in producing a titanium build that worked as it should. On a side note, I didn’t notice any difference in flavour intensity or resolution at all, maybe it’s my building skills, maybe just my taste buds. Now the question is, while “priming” (that’s what it’s called? I tend to forget…) - I mean heating to a very faint glow at low wattages in dark environment - I noticed that only the most central two or three wraps out of 5-6 were showing that faint glow, and only those wraps changed in colour. The coil works fine, it produces vapour and nice flavour, I can control the temperature alright and all. I’m just curious if this is normal or whether I should decrease the gap size between wraps? I’ll upload a picture when I get the opportunity.
Tagging @Pro_Vapes because he’s the Titanium Man, in my impression :grinning:

Secondly, this sparked my interest. Can anybody tell me why coils heat up from the middle first? I mean at a fundamental level. Why is that? This could help us (or me…) find better ways to prevent hot legs…
Tagging @BoDarc , @therabidweasel and @Whiterose0818 for their technical knowledge :wink:

Any input much appreciated!

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As the electrical energy passes through the coil it begins to heat up and at the same time dissipate the heat. as the heat dissipates in all directions from the coil, the most intersects in the middle of the coil.


The coil heating from the middle is good. If you were to continue to heat it more, the entire thing would glow red.

I do not know on a fundamental level why this is how it is when it is built correctly, but I too would be interested to just know.

If it is heating like this, it is working just fine.

Are you noticing any other issues?

Nope, working just fine. I was just concerned that my not being overly impressed with titanium coils’ performance is in fact due to faulty construction - I’m concerned that only the central two or three wraps are actually vapourizing stuff.


I assure you, the entire coil, is nearly the same temperature, it is just concentrated in the center. I am not familiar with the physics of electricity in our coils, I just know the precaustions and enough to not blow myself up.

I have been putting off titanium coils as I am not 100% on how safe they are.

If you could solve that, I would be very interested in trying some.

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I also switched to Ti1 this week and had the same concerns. Thanks for asking the question.

It’s rather safe if you know what you’re doing (and cleaning it before building). The thing to be concerned about is titanium oxide forming at high temps (like a Kanthal dry burn at high watts). Someone over here contends even that isn’t a big concern (sorry, I forgot who said that exactly…). Lots of info on titanium safety over at the big titanium coil thread over here and on ECF. :slight_smile: Give it a try.

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What concerns do you have about Ti? Kanthal is an alloy consisting of aluminum nickel and chromium. The “char” you see on your coils consists of aluminum oxide. Dry hits can release these oxides into your lungs and into your blood stream. Your body cannot expel Aluminum and it can wreak havoc on your CNS. A diet high in Omega 3 and 6 (fish, chia seeds,hemp oil) will allow aluminum to pass through the blood brain barrier and be released in your hair folicles. Titanium oxides however is readily expelled from your body through your finger nails and so on. Not to mention Titanium dioxide is get ready (FDA approved-lol) and is used in food products all the time as a de-caking agent and whitener in powdered coffee creamers. Also, since the purpose of Ti is to run temp control you will be hopefully all but eradicating dry hits. Just my understanding from my research,not Gospel, just my 2bits


What gauge, temp, watts, and mod are you using?

24g 2*5/6@3mm, clocking in at 0.13 (ohm reader) or 0.18 (DNA200, Panzer) or 0.10 (Yihi 350j v2). I dry fired it at 7-10W on the DNA200 in Watts mode. Currently using it on the 350j v2, single Basen Black 26650, resistance set to 0.10, temp 500F (I’m not hitting the temp limit, as far as I can tell), 35J, standard pre-heat.

Before, I had good results with 22g, as well, thanks to your write-up :grinning:
I came up with the above build by playing around with wire gauge and wraps until I found something that would produce green heat flux somewhere around 35W.

I think I’m a little more hardcore, vaping around 580-600F and about 85W. When I first started Ti, I vaped the 24g / .50mm and I was pretty happy with it. But when I went the 22g there was a big difference.

I’ve never noticed gap size to make a difference.

I glow the 22g in short burst. Most times only a few wraps will glow at the start. I continue the short burst until all wraps glow. 22g is the only TI I will glow. I’ve had coil meltdowns with lower gauge Ti.

Why did you switch up 24g?

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I think the gap does matter but can be narrow or wide just so the power cant jump across. On some coils, if it isn’t glowing right, you can strum the coil to get the glow. I like tight spaced coils.

Yes right gapped vs non-gapped does make a difference, but gap size has never made a difference. I’ve been building .05-.08 ohm coils for at least a year and how much spacing has never made a difference. I space based on my RDA/RBA size, but initial coil is always the same before spacing and always ohm out and perform the same.


Excellent! Precisely what I needed to know. :triumph:

OK, I’ll try that next time!

With “good results” I meant it was a working coil that produced nice flavour and volume. I don’t like it that hot, though, so I switched to thinner wire. I found that with 22g, if I want to vape at a comfortable temp and wattage setting, I need pre-heat to get the coil going, but somehow - I have really no idea why - I don’t enjoy a vape that’s strong at the beginning but trails off afterwards. Even if the intensity in the beginning is uncomfortable, something in me doesn’t want the vape to trail off :thinking:

So, in conclusion: I’ll try to pulse them more to get all wraps to glow a little the next time I build. :slight_smile:

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I totally understand. You should vape what’s comfortable for you. I hope it all work out for you.

@Naseschwarz I have made many Ti coils and the thing I learned was using less wraps. The wire is so low resistance that the inner heat happens way before the outer wraps and TC seemed to be affected and gives weak performance. By that I mean I get singed cotton too soon (lifecycle of the build) without much vapor ( I vape lower temps and lower watts and get plenty of clouds)

I have consistent results with 4 1/2 wraps (spaced) of 22ga @ 3.5mm ID. Just last night I took a Smok TF-RDTA out of retirement and wasn’t happy with the results. I cracked it open to find a freshly built 6 1/2 wrap 22ga Ti dual setup. I just took the existing coils off and unwound a wrap from each end (down to 4 1/2 wraps) and rewicked. It’s working great on my Vt133 @ 36 watts 410F …detecting in “Deep Water” zone @ 0.08 ohms

This is just my experience with my ancient lungs :wink: but with more coil wraps Ti seemed to burn the cotton in the center before chucking my level of desired vape …which is low. Also have to mention I removed the cotton and rewicked with HEMP on this occasion, but the 4 1/2 wrap decision has been a year-long testing deduction (cotton or rayon and now hemp). To clarify “4 1/2 wraps” …when viewed, the outer coil show 5 wires and the post side show 4 wires + legs (and always spaced)


That sounds good! Will try that next rebuilding session! :sunglasses:

I’m the (main) one that contends titanium is covered by an extremely tenacious coating of titanium oxides…on elr at least. Any materials textbook will tell you the same, and you should look it up! It’s oxides, like those of aluminum are those two metals version of iron’s rust, which is iron oxide. However, as we all know Al and Ti don’t rust, which is due to the fact that they posses this tenacious coating of Al or Ti oxide. The only remote possibility one would generate ANY particulate (oxide, nano, otherwise) is if they were to short a build and blow the coil. When this happens your cheeks puff out. I have a doctorate that includes chemistry and have dealt extensively in the research of creating and utilizing the much feared “nanoparticle,” of titanium oxides and many others. THAT ain’t happening. Take it to the bank. Don’t blow your builds, you have no worries. If you do blow a build, the burning juice or wick concerns me more, but I inhale metal vapor during every drive I take, at minimum. One blown coil isn’t going to take many seconds off my life…I’m inhaling a dilute poison already called nicotine.

I apologize for going full nerd and explaining now why your coils glow in the middle, but I love this stuff. Firstly I will say I use Ti1 exclusively and never dry fire. That said, doing so should only improve that lovely inert coating on the wire as long as one is very careful not to blow the coil. If that happens you gotta build again, nothing else. . well, I suppose the mod might take issue with it, but it’s not too likely.

Heat is transferred via convection (fluid currents as in air or water), conduction (direct physical contact), or radiation (glowing in the infrared, ie heat you can feel or even visible light ie. “red, white, blue” hot etc.)

Conduction is by far the most efficient method of transporting heat. Titanium has a fairly high thermal conductivity. The legs of the coil are cooler because they are conducting their heat to the cool post of the atomizer better than the center of the coil. The center is hotter because it is further away from the posts in terms of conducting heat down the wire’s length.

To geek out just a bit more, the hotter center of the coil drives a phenomenon called natural convection…basically hot air rises. That means the center of the coil is transferring heat better than the legs via convection. However, as I mentioned conduction is by far the most efficient mechanism, and thus, it’s effects are much more evident.

You all also know by now, that some of that heat is coming out as light and (in part) being seen as a soft red glow by your eyes…the center is working better via radiation in this case too, but radiation is a much less efficient method of heat transfer than the other two.

All of that said, I advise you to scrutinize what you read. Pay attention to the detail or lack thereof. Do those details form a cohesive story that convinces you what you are reading is true? Googling key points (like “heat transfer” for this post) and looking at reliable information on them is worth the effort. I will try to remember to post some links. Much love.


Ah, brilliant! Exactly what I wanted as an answer! :blush: Thank you!

There’s one part I didn’t quite understand: [quote=“therabidweasel, post:18, topic:102248”]
the center is working better via radiation in this case too

Why is the center of the coil better in radiation, too?

Got a follow-up question (or two) as well, if you don’t mind (you seem to enjoy this :wink:):

  1. Why does strumming the coil help with even heating? I read that’s because it evens out tension, if memory serves. But what does tension in the wire have to do with heating? Is it, perhaps, due to the fact that inside the wire there are parts of the material with impurities that reduce/increase conductivity a little - then, when the wire is under tension or twisted, this would create uneven “flow”… does that even make sense? :thinking: (sorry, I’m not from a technical background)
  2. When making contact coils, it happens that in the beginning some of the wraps heat up earlier that the others - supposedly due to electricity moving “sideways” between wraps instead of going through the wire lengthwise (?). Now, experience tells us that pinching the coil evens this out - but why?


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The radiation is the glowing, so in simple terms the brightest portions are dissipating the most heat via radiation. You can calculate the temperature from the color using Wien’s displacement law. It gives insight into radiation in general…and everyone knows that white hot is hotter than red hot. This is the math, don’t let that overwhelm you, just read the words. Nifty article:

Regarding strumming, I have no theories and certainly no facts, but I’ll think on it.

As far as contact coils…yes electricity is moving sideways but it’s not jumping. Imagine your coil up close, just two loops. Before you really meld them together while red hot, pushing them together cold only gets them to contact at certain small points around the loop. At those points the current is flowing across the two coils. As you heat and press the coils together you make better and more stable electrical contact and the current flows through the coil more evenly, that’s assuming kanthal. That very adherent titanium oxide from above? That’s an electrical insulator. If you heat a Ti coil you produce varying thicknesses of titania along the wire (that feared highly adherent oxide), and a particular one of these oxides, TiO2, is a transparent material used to make laser grade mirrors. The coil discoloration is in part due to this effect and is 100% analogous to the colors from dropping oil on water, you can Google newton’s rings on that…same effect on your coil. Anyhoo, by heating your Ti coil you’ve now grown an oxide on the wire. Were you the try to push it into a contact coil, you would not see the same effect as kanthal because of the electrically insulating nature of that oxide would prevent the coils from connecting electrically, but this would be difficult to see with your eyes because you’d need the coil hot enough to see well, which will pretty much blow your build.

All that said, who is still using contact coils? Those are sooo late 2015, lol.

Hey, thank you for the questions. I don’t know everything as you can see above. Thanks for being cool about me posting all this. Heat transfer has somehow become about 50% of my job in a bunch of weird situations. For instance, spacecraft, because they live in the vacuum of space, can ONLY dissipate heat via radiation as there is no fluid (eg air) or anything to contact the craft that could conduct heat away. I think this is really cool simple stuff that people already know from experience, I’m just trying to explain the basis of it all. It’s really not rocket surgery because everyone has experienced these things via our hobby. So I hope you guys like this stuff :slight_smile: