E-cigarette technology has been advancing at an incredible pace over the last few years, and it shows no sign of slowing down.

Early devices were either mechanical or delivered a constant, regulated voltage to the atomiser.

Then came variable voltage mods, which let you fine-tune your vape exactly the way you wanted.

The next upgrade to that was variable power, which did basically the same thing but in a more convenient way – the mod could detect the resistance of your coil, so even if you changed coils it would automatically adjust the voltage to maintain the power output you were looking for.

The latest vape mode to be introduced is temperature control, or TC, and, as predicted by P Busardo in our 2015 e-cig predictions, it’s rapidly becoming a must-have feature on new box mods. The first temperature control chip was the Evolv DNA40, released just last year, but already there’s a respectable and fast-growing assortment of competitors.

The basic principle behind temperature control is simple.

Instead of selecting the voltage or power output the mod should deliver, you set the temperature you want the atomiser to run at. When you press the fire button the mod monitors the temperature and automatically adjusts power to bring the coil up to that temperature as fast as possible, then keep it there.

TC is the next logical step.

After all, the temperature of the coil has a huge influence on how your vapour tastes – too hot and it’ll start to taste burned, too cool and your liquid won’t evaporate at all. Meanwhile, the ability of the device to keep the coil at that temperature will affect how much vapour you get.

If your amazing wick is delivering more juice than the coil can cope with the temperature will drop. On the other hand if it can’t keep up the temperature will rise rapidly until you get a dry hit – and that isn’t good news. Obviously, if you can set the coil temperature and it then stays constant it’s going to be much easier to get the vape you’re looking for every time.

Working within limits

There are some technical challenges, of course.

The biggest one is that mods don’t actually have any way of sensing how hot the coil is.

It would be possible to build an atomiser with a temperature probe built in, which could then send that information to the mod’s chip, but there’s no way to make that work with a standard 510 connector – it just doesn’t have enough contacts. A 510 fitting only has the positive centre pin and the negative screw, and they’re both already tied up carrying power to the coil. Temperature control would be a lot less attractive if it meant saying goodbye to all your favourite atomisers because they couldn’t take advantage of it.

Luckily Evolv came up with a way around this issue, and the same technique is used by all the other TC chips now on the market. It’s based on a characteristic of metals that’s been well known for a long time, especially to anyone – like Evolv – who makes electronics. The resistance of a piece of metal – like your atomiser coil – isn’t fixed. It can vary under some circumstances, and one of those circumstances is a change in temperature.

*Science alert*

Metal is a good conductor of electricity because each atom’s electrons aren’t tightly bound to it.

When there’s a voltage difference between each end of the metal the electrons are attracted to the positive terminal and move in that direction, allowing the battery to feed in more electrons through the negative terminal. The electrons can’t move completely freely, though; they do have to push their way through a mass of atoms which are all vibrating slightly.

If the temperature rises there’s more energy in the metal and the atoms vibrate more energetically, so it’s harder for the electrons to force themselves through. In simple vaping terms, the resistance has increased.

So your TC mod isn’t actually measuring the coil temperature; it’s measuring the resistance – which all modern mods can do anyway – then tracking how it changes. Unless you’ve frozen your mod to liquid nitrogen temperatures (which we don’t recommend) the relationship between the two is very predictable, so from the increase in resistance the chip can easily work out the increase in temperature.

Purity is a virtue

The chip’s ability to work out what’s happening to the coil has limits, of course. For one thing it can’t, with a few exceptions, tell exactly what the coil is made of.

This is a problem, because different metals – and especially alloys, like kanthal – change resistance at different rates as they heat up. For TC to work the coil needs to be made of a pure metal, not an alloy, and not all pure metals are suitable.

The first coils suitable for temperature regulation were made of Ni200, a high purity form of heat-treated nickel wire. Ni200 is still the most popular material for these coils, although titanium is now increasingly common. Both of these metals are heat-resistant and have very good conductivity, so they’re ideal for making coils that will stand up to the demands of high-power vaping.

Right now it’s not possible to build a chip that can analyse the coil and tell what kind of wire it’s made from, but it is possible to make one that can recognise one or two specific types based on their electrical characteristics. For example the iStick TC40W can identify a nickel coil, and if it does temperature control mode will be available. Otherwise it will default to VW mode. Many other devices can also detect titanium (Ti) coils, and switch to a TC mode optimised for them.

Are Nickel Coils Safe?

There have been some concerns about whether nickel coils are safe. There appear to be two main concerns - could Nickel leech when hot or exposed to e-liquid, and could there be an allergic reaction to nickel.

Much of the concerns have arisen from this video here.

The video generated a lot of discussion. Unfortunately, the video comments have been disabled, but there have been several counter arguments. A great summary of them can be found here. In essence, they say that the conditions needed for nickel to be a concern do not exist.

I also spoke to Tom Pruen, Scientific Officer at ECITA. He told me:

Since Nickel is already a major component of e-cig coils, and levels of it found in collected vapour have, so far, been extremely low, the use of an entirely Nickel coil would not seem to significantly increase risk. In fact, the use of Nickel coils in TC mods would, logically, reduce risk since the coil temperature is likely to be linked with the emissions of metals, and this is less likely to be extreme in a TC coil. This would have to be reviewed once direct data is available, but for the previous reasons, the data is more likely to be reassuring than concerning.

Firing it up

A TC mod will have a menu option that lets you switch from VW to TC mode; on the iStick you do it by holding down a small button between the up and down controls. You can then set the temperature exactly the same way as you’d adjust voltage or wattage.

You’ll find there’s a range of temperatures available – the iStick TC40W lets you choose from 300-600°F or 100-315°C. A lower temperature will give you a cooler, less dense vape; higher temperature means warmer, thicker clouds. Like VV or VW, it’s best to start low then adjust upwards in small increments until you hit the sweet spot.

When you’re in TC mode the mod’s display will change to show the appropriate information. On the iStick, when the mod isn’t firing it tells you what temperature you’ve set. Press the button and it changes – instead of showing how long you’ve been firing for, as it does in VW mode, it shows you the actual coil temperature.

This rises at an amazing rate as soon as you press the button until it reaches the setting you chose, then the C part of TC kicks in and the screen shows “TempProtection”. In TC mode the display also shows how many watts it’s taking to reach that temperature, which is always nice to know.

So is it worth it?

Vaping with TC obviously isn’t as simple as buying a new mod and setting it up for the perfect temperature. You’re going to have to change your coils too, and potentially your atomiser – although the choice of atomisers that take Ni200 or Ti coils is increasing fast, it’s more or less limited to the new generation of sub ohm tanks. If you’ve been happily puffing away on an old Protank 3 for the last couple of years you’re not going to find compatible coils for it.

So does the new technology justify the cost and learning curve?

The short answer is yes, it does, for two reasons.

Firstly, temperature control gives you a more consistent vape. Once you’ve experimented with it a bit, and found the setting you like, it irons out a lot of the variation inherent in vaping. If you want a device that hits the same way every time TC will deliver that – and it will keep on delivering it down to the last drops of liquid in your tank. Many vapers enjoy tinkering with their gear to get the ultimate vape, but plenty more just want a safer, no-hassle alternative to smoking.

The other reason might not actually be the most important, but it’s going to be seen that way by the public health community because it relates to safety. It’s pretty clear by now that the reason some researchers have found high levels of formaldehyde in e-cig vapour is because their experimental technique was causing repeated dry hits. Obviously nobody’s going to keep vaping under those conditions so the real-world risk is very low, but that isn’t how the sceptics see it. As far as they’re concerned, there’s a way to set up a mod so it delivers an unwise dose of formaldehyde.

Using TC neatly solves that problem. Dry hits happen when the ability of the coil to vaporise liquid outruns the wick’s ability to deliver it. Without enough juice around to cool it the coil temperature rises rapidly and what liquid is left – and sometimes part of the wick – gets burned. As any smoker knows it’s combustion that creates most of the carcinogens, so it should be avoided. With temperature control it will be avoided, because as soon as the mod detects a sudden rise in temperature it lowers the voltage to compensate. The coil stays at the correct temperature, the wick is safe and those last droplets get vaporised properly instead of incinerated.

With TC, dry hits are a thing of the past.

What are the options?

When temperature control first appeared it was only available with the DNA40 chip, and getting one of those usually meant either buying an expensive box mod or digging out your soldering iron, ordering a chip and giving your old DNA30 device an upgrade.

Now it’s very different.

Almost every manufacturer now has one or several devices featuring TC mode. Some of our favourites include the Geekvape Max 100, Smok G-Priv 4 and the Voopoo Argus GT II.

Your next decision is what sort of atomiser to use. Sub ohm tanks are the fastest-growing sector right now and they’re perfectly suited to TC vaping. Ni200 coils are available in both Kanger Subtank and Aspire Atlantis styles, so there are quite a few tanks out there that will take them. You won’t find them for older tanks though.

While you could try making your own it’s not a great idea. Nickel and titanium are both extremely conductive, and any coil you could make with them that would fit in an Evod head would be sub ohm. Older tanks aren’t suitable for high power vaping, so don’t try this.

It’s a different story with rebuildable atomisers, either drippers or tank styles. Keen vapers have been putting low resistance builds in these for a while now, and if you get some Ni200 or titanium wire you can put together a TC-compatible build.

These wires have some quirks though.

If you’re used to winding contact coils, where the wraps touch each other, you’re going to have to get out of the habit. This is bad practice with TC; the mod’s temperature reading is an average across the coil, and if two or more wraps are touching each other they’ll short. That fools the chip into thinking the coil is cooler than it really is, and it’ll crank the power up to compensate.

You’ll probably also have to work with thinner wire than you’re used to, otherwise the resistance will be extremely low, and nickel can be fiddly stuff to work with – it’s quite springy, and can also stretch slightly if you put too much tension on it. Stretching will reduce its diameter and increase resistance, and this can create hot spots on the finished coil. Again, if you enjoy fiddling you’ll have a lot of fun making TC coils. Otherwise a tank with premade heads is probably your best bet.

The heat is on

Temperature control is here to stay. It has some real advantages over earlier devices, including banishing the spectre of dry hits. The difference it makes to both safety and the enjoyment of vaping is fairly conclusive, which together with the average vaper’s love of novelty is helping the technology spread with amazing speed.

From a high-end item in 2014 it’s now available in entry-level box mods like the iStick, and a year from now non-TC mods will almost certainly be in the minority. That’s not to say all their owners will be using that feature, but as the technology improves and the choice of atomisers expands more and more of them will be. Just like VV and VW before it, TC takes vaping a big step forward. If you haven’t already tried it, you should look for it in your next mod.

Also see:

https://www.ecigarettedirect.co.uk/ashtray-blog/2017/02/sub-ohm-vaping-beginners-guide.html