When you say the mod will not allow the atty to pass 1.424ohm as the mod does not care about temp it is reading your TCR value against the cold coil value. We are going into TFR territory here and that is why most use Steam Engine DNA file to upload to their device and call it a day.
As Mike said TCR is less accurate by nature than TFR so let’s not complicate it and I have locked the cold resistance anyway.
What we are aiming for should be in the current reading:
TCR is 80 The mod is saying 400F, the thermocouple is saying 400F, no overshooting happening. When I take a draw is it still holding 400F or not and how to address that issue if it happens.
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No we are not entering TFR territory.
Both Temperature Coefficient of Resistance (TCR) and Temperature Factor of Resistance (TFR) operate in the same fashion. If we know the metals cold resistance, we can calculate the metals temperature due to any changes in that resistance based on the metal TCR/TFR values. As the metal heats, it’s resistance increases. As it cools, resistance decreases. This is not vaping technology but has been adopted by the vaping industry. TFR is a more accurate method, but that will be dependent on the metal used. Because you are using TCR, lets ignore TFR.
A vape device does not read the coil temperature at all. If it had such functions we wouldn’t need TCR values. Set temp and forget.
With a vape device a delta resistance is calculated based on your coils cold resistance, the TCR value that was inputted and the prescribed temperature. Example:
0.5 ohm coil, TCR value of 0.001 and a prescribed temperature of 200°C yields a delta resistance of 0.587 ohms.
The device will apply power until resistance rises to 0.587 ohms to where the device will then modulate power to maintain that 0.587 ohms. Airflow and wick saturation have an effect on how quickly the coil rises in resistance. Less airflow and saturation the greater the rise, but the device still does not allow the resistance from exceeding 0.587 ohms.
Now lets say our 0.5ohm coil’s true TCR value is 0.00088, but we continue to use 0.001 and set a goal of 200°C. The device calculates a delta resistance of 0.587 ohms. This is a +0.087 ohms increase based on the calculated values.
BUT…because the coils true value is 0.00088, +0.087 ohms results in a true temperature of 224°C. The delta resistance is maintained but due to the incorrect TCR value our temperature is also incorrect.
This displays why your temperature measurements did not match that of the device and stresses the importance of using a correct TCR value should one wish to vape at an accurate temperature. To note, the accuracy of coil resistance and reading the rise in resistance also skews the results.
Now lets look at your case and analyze why such a large discrepancy between temperatures with cap on vs cap off?
Ignore the incorrect TCR settings. The coils true TCR was established to be 0.0008. With the cap off you were able to reach 485°F. With your 1.22 ohm coil, and a true TCR of 80 this is an increase of +0.22 ohms. Or 1.44 ohms total.
With the cap on your coil could only reach 365°F, that is only an increase of 0.15 ohms or a total of 1.37 ohms. The incorrect TCR value of 93 plus a set temperature of 400°F allowed the coil to reach 1.44 ohms but did not allow it to reach 1.37 ohms. Why?
So either the airflow of your atomizer is preventing the coil to rise in resistance (hence temperature) or your thermocouple was incorrect. To me, this discrepancy stresses the importance of taking the measurements again with the cap on.
But if you are content with how it vapes, then that is up to you but understand that if your coil is not reaching the delta resistance, then you are not hitting your objectives and your device will not modulate power accordingly.
That post was waaay too long! I need a drink!