Q&A: TC precision

      2 Comments on Q&A: TC precision

What exactly does TC precision entail? Is a higher value more desirable, or lower?

The TC precision number in the Wire Wizard is an attempt to describe how easily a mod can sense the temperature of a coil. A higher number means that you should have more precise temperature control.

The number is the product of the two most important factors for temperature control; the TCR and the base resistance. It is calculated by multiplying TCR * R * 1.000.000.

To expain the reasoning behind this calculation, let me first give you a technical fact, which is true for all electronics:

As long as the resistance is not too low, it is easy to measure it with reasonable accuracy. But if the resistance gets too low, accuracy goes out the window, unless you start employing some special techniques, like four terminal sensing. Mods don’t have the hardware for this.

Here are two practical examples from temp control coil building:

Ni200 has a very high TCR, which is good. This should make it easier to measure the change in resistance. At the same time, Ni200 has a very low base resistance, which makes it hard to measure the resistance accurately to begin with.

Titanium, on the other hand, has a lower TCR. It also has a much higher resistivity, which gives the coil a higher base resistance. As the temperature rises, the resistance does not change as much in relative terms, but because of the higher base resistance, the absolute change in resistance is still significant.

So: When the mod has a larger cold resistance to calibrate to, and a larger absolute resistance range to work with, all the internal resistances (of the mod itself, the 510 connection, the atomizer, and the coil post connections), will become less significant, and contribute less error.

In principle, this should – potentially – lead to a more precise temperature control. And that’s what the TC precision number is an attempt to convey.

By the way, the only purpose of the factor of 1.000.000 is to bring the number up to an easily readable range.

2 thoughts on “Q&A: TC precision

  1. Richard

    If I go to Wire Wizard with ID 2.5mm 4.5 wraps “Clapton” 26 inner 32 outer both K A1, for this small coil, it says I need 100 watts for 200 mW/mm² heat flux (2.05 mW/mm²). Info is very scarce and some other users have different heat flux from their shady mobile apps. So to you as an expert, can this little coil really be that thrash and should I look around for higher gauge outer wrap wire like 40 AWG? Also is heat flux the most important data to optimize coil or are some other stats like heat capacity important as well? Very grateful for your site and admire knowledge you put into the site and moreover the simplicity and purity of the design.

    Reply
    1. Dampmaskin Post author

      Thanks for that. The heat flux calculation in Steam Engine uses all the surface area of the wire, while others may just use the core wire which will give a higher heat flux at lower wattages. The “truth” probably lies somewhere in between. Heat capacity certainly has an influence on how hot a coil will taste, a high heat capacity can “hide” the heat flux for a couple of seconds until the coil heats up. That’s how the temperature is controlled with a mechanical mod: The user adjusts the length of the button press to control how hot the coil will become. After you’ve taken a long drag with a mechanical mod, the next drag will have to be shorter, unless you wait until the coil has cooled down again. That’s the heat capacity doing its thing.

      Reply

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