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High Tempature Hotend Thermistor  

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R. Stone
(@r-stone)
New Member
High Tempature Hotend Thermistor

My original thermistor deteriorated, the material holding it in the 3mm brass tube turned to ash. I decided to upgrade to a high temperature one an online seller stated was compatible... then in the fine print included the small detail of having to modify your firmware... Marlin firmware has a temperature table for this device listed as thermistor 66. I copied the contents of that project's thermistor_66.h to Prusa's thermistortables.h (firmware 3.9.3 is the latest release that works with my printer) modifying the format to match the prusa style entries and converting numbers to integer values. I also modified the line defining my temperature sensor in variants/1_75mm_MK3-EINSy10a-E3Dv6full.h #define TEMP_SENSOR_0 66. The firmware mod seems to have worked but I am now getting a mintemp error that will persist even If I change the mintemp threshold to zero and uncomment #define DEBUG_DISABLE_MINTEMP in the file for my variant. performing a factory reset and selftest reports an error that the heater/Thermistor is not connected. All connections were checked and resistance value for thermistor verified as 4.4Mohm at room temp.

Is this resistance value too high? am I overlooking something?

Posted : 23/12/2022 10:26 pm
Artur5
(@artur5)
Reputable Member
RE: High Tempature Hotend Thermistor

If you look the questions/answers of the buyers of this thermistor, you'll find  this one :

Question : Is this a ntc or ptc, what is the ohm rating and the 25c ??

Answer:  Not accurate under 200 Deg C so don't rely on the 25C resistance, just use 66 as the thermocouple reference in marlin and you'll be good for 200-450C

I have no idea if that answer is correct but, if it is, then it explains why you get a min. temp error. This thermistor would be totally inaccurate measuring the room temperature when you switch on the printer.

 

 

Posted : 24/12/2022 9:46 am
R. Stone
(@r-stone)
New Member
Topic starter answered:
RE: High Tempature Hotend Thermistor

Yes, it definitely could. The info screen shows a value of 0 for hotend temperature which could throw that error. I attempted to suppress with DEBUG_DISABLE_MINTEMP but the error was still being thrown.

Posted : 24/12/2022 11:05 pm
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