Temperature Control (TC) is the mode through which the box/mod regulates the intensity in order to keep the coil at a temperature that is defined by the user. According to the manufacturers, maintaining the temperature constant is the guaranty of more safety but this argument is sometimes misused since, for example, no indication is given, neither on devices nor on juice bottles, regarding the temperature to use.
Basic knowledge on material science
A coil is most of the time
a resistive wire that is folded in a spring-like cylinder with non-touching circular turns. The wire’s
resistivity (in Ω.m-1) defines how strongly a given wire, generally an alloy, opposes to the flow of electrons, or
electric current.
Heat is produced when electrical energy is dissipated into the wire when electron are scattered by the atoms present in the alloy, the so-called
Joule effect
The joule effect is a physical law that describes the relationship between the heat generated and the current flowing through a conductor.
The temperature reached by the coil is directly proportional to the square of the current intensity (U2) and inversely proportional to the value of the resistance (R).
Application: For a given resistance coil (value in Ω), a higher temperature is reached when increasing the intensity (voltage). But if you keep the same voltage, a lower temperature will be obtained with a higher resistance value.
">Joule effect.
When you purchase a coil from a vendor, it comes with a label showing its
resistance, a value in Ohm (Ω).
The resistance of wires changes with temperature
Relationship between resistance (R) and temperature (T) for a resistance coil
The resistance of an alloy is stable near room temperature and generally increases with temperature as the material becomes a superconductor. Then, and only after this transition, its resistance can be predicted from its temperature.
It is also possible to use the revert relationship to reach a setpoint temperature. And this is exactly
the principle that uses your favorite mod when switching to temperature control.
The temperature control
As a general rule, the resistance (R) of a coil increases with temperature (T). In the
temperature control mode, the chipset of the box measures on a very fast rate the resistance when incrementing intensity levels. The chipset basically increases the intensity of the current up to reaching a certain value (R) of the resistance. This setpoint value (R) corresponds to the desired temperature (T).
Relationship between the Resistance (R) and the temperature (T) (see the text for more information).
However, to obtain this temperature (T) with more or less of accuracy, the procedure strongly depends on the
calibration parameters.
In the
calibration procedure (generally an operation that is made manually and that is more or less described in the user manual), the nominal value of the
resistance (R0) is measured by the device at
room temperature (T0) and the
temperature coefficient of resistance (α) is selected. For the sake of simplicity, manufacturers offer the possibility of select α from the type of resistive wire used: Nickel (Ni), Titanium (Ti) or Stainless steel (SS).
In some more expert modes, α can be entered as a numerical value. This allows using types of alloys that are not common or to adapt to new resistive coils to come on the market without changing one’s box.
When is it recommended to use the TC mode?
Ni, Ti and SS coils are compliant with temperature control but not Kanthal. The reason why Kanthal does not allow temperature control is because this FeCrAl alloy has much more impurities than any others and does not offer superconductivity properties (a linear relationship of resistance with temperature). In fact, the electrons are so scattered by the impurities that they heat the alloy while the resistance is kept constant. Special grades of Kanthal can be used as high as 1,425°C in the industry.
Is the temperature control precise and accurate?
No. But it is better than nothing.
The parameter α is fitted from measurement data in a defined experimental setting that does not necessarily meet the conditions that are used with an e-cigarette. Hence, α is dependent on T0. Since the box is not equipped to measure this temperature, α is set as a constant by the manufacturer. Hence, if you calibrate your box at 17°C or 27°C, the accuracy of the T:R relationship will vary. Remember that the linear approximation is only an approximation and is different for different reference temperatures T0.
Such warnings should call users to use caution when selecting their working temperature and to keep a bit of freedom with what they choose as their higher limit.
What temperature to select?
The lowest as possible… Right, but depending on your device and the juice you vape, a minimum of heat is needed to produce vapor. In mixes, different liquids are present with different properties and boiling points.
Water boils at 100°C,
Propylene Glycol (PG
Propylene glycol
">PG) is vaporized at 188°C (or 371°F),
Vegetal Glycerin (VG
Vegetable Glyceryn
Vegetable Glycerin is a colorless, odorless, and tasteless viscous liquid that is used in pharmaceutical formulations. VG is exclusively derived from plants (soybeans or palm), since some can also be of synthetic origine or come from animal fat. Glycerol is an additive (E422) used in the food industry and a thickening agent or a preservative. Its sweet taste makes it a sugar substitute present in low-fat products.
">VG) at 290°C (or 554°F) and
ethanol at 78°C (or 173°F).
Other constituents are also present whose concentration and composition are also very variable from one juice to another.
The most common is
nicotine whose concentration cannot exceed 2% in Europe, but with values up to 4.8% in certain juices like those used in the Vype ePen, for example. Nicotine’s boiling point is reached at 247°C (or 477 °F).
Flavorings can reach up to 20% in volume of the final blend. Diacetyl
Diacetyl or butane-2,3-dione ((CH3CO)2) is an organic compound that is a by-product of fermentation.
Diacetyl is naturally present in alcoholic beverages and is used as a buttery flavor in the food industry. This flavor is also used in the elaboration of receipes of e-liquids.
Despite innocuousness when ingested, diacetyl has proven harmfulness upon inhalation. Some employees of manufactures using artificial butter flavoring have been diagnosed with bronchiolitis obliterans, a rare and serious disease of the lungs associated to this compound.
Together with acetylpropionyl, diacetyl is of legal use as a flavoring substance in the European food industry but their use is controversial in e-liquids for their potential harmfulness (Farsalinos et al., 2014).
">Diacetyl, for example, that gives a buttery taste, boils at only 88°C (or 190°F), for acetoin giving the same flavor, it is higher (148°C or 298°F). For the flavor of banana, isoamyl acetate is vaporized at 142°C (or 288°F). Benzaldehyde (cherry taste) boils at 178°C (or 352°F) and cinnamaldehyde (cinnamon taste) at 248°C (478°F). Fruity flavors (ethyl propionate) boils at 99°C (or 210°F), grape (Methyl anthranilate) at 256°C (or 493°F), orange (limonene) at 176°C (or 349°F), Pinnaple (allyl hexanoate) at 190°C (or 374°F), cotton candy (ethyl maltol) at 161°C (or 322°F), menthol at 212°C (or 414°F) and vanilla (vanilline) at 295°C (or 563°F).