Jbc T245 controller number a million

[sahko123]

As is made clear in the title I'm designing a t245 controller/driver. My goal was to use as small a transformer as possible so I'm going to use a 140w flyback smps design for the power supply using a yet to be stocked/probably sourced from ADI directly lt8357 controller.

I want it to be digitally controlled most likely using an arduino nano with an adafruit oles for shits and grins while being driven using pwm using mosfets to be as efficient as possible. Looking at an efficiency of around 85% or higher (not really sure how good it will be as of yet will measure when made and update).

My current issue is trying to find what type of thermocouple is used some people say K type others say N Type but some claim neither since the actual thermocouple doesn't measure close enough to those two types to actually be one of them. In a random post I found (https://electronics.stackexchange.com/questions/534554/how-to-amplify-a-thermocouple-that-shares-a-wire-with-a-heating-element-solderi ) someone who says nichrome-copper (18.5uv/c)(the closest measurement I've found of these cartridges was 15.7uv/c which may be within margin of error). I'm not sure which type of thermocouple this ends up being. Chances are I'll have to do software defined cold junction compensation with an external absolute temp sensor and some calibration procedure for extra accuracy. (looking to within 5c)

Does anyone have a better idea of the type of thermocouple present in the C245 cartridges? (I have them on the way but don't really have the set up to test it accurately).

[RoGeorge]

I remember C245 to generate very low voltages, something around 1mV/100*C.  Certainly it's not something common like type K, J, etc.  You'll need a chopped op amp (auto-zero) for sure if you want to set accurate temperature (aside from the cold junction temperature readings).

Though, temp accuracy doesn't matter that much when soldering.  Temp accuracy is more a thing of show-off and benchmarks.  What matters the most in practice is the thermal resistance and the thermal power of the tip (which is not the same as the electric power).

[sahko123]

I do want it to be at least precise and accuracy can be basically cal'ed into place. I want precision for various software systems to be able to get a good level of control over the irons performance.

One feature I want to have is immediate power proportional to the decrease in temperature. So the faster the temperature drops when the iron is used on a powerful heat sink the harder the iron is pushed.

Anything that I do that seems like over-kill/over-engineering is basically just for fun. This is why I want to be able have as much data available from the iron to use. Even now I'm trying to optimize the OLED controller section to be able to get as fast an update rate as possible to have more time to make changes to power output based on measurements.