(Extruder-) heating at very low temperatures (

edited December 2018 in Extruder & Bed
Hey Forum,

I have a problem, and i guess it's not a very common one :D
I'm kind of "misusing" the Repetier Software on an Arduino and the corresponding board. For a test-setup in a laboratory i need a reliable heating device with included PID and multiple different temperatures.
I'm controlling the Arduino with the repetier-software with LabView and the VISA interface (simply sending GCODE and reading temperatures with M105). No problems here, everything seems to work nicely!

But the problem: the whole setup is cooled and only a small part is heated very specifically. As the cooling is well below 0°C it also happens, that my heater is below 0°C. I changed several options in the configuration.h file so i don't have problems at negative temperatures.
#define MAXTEMP 275
Interestingly heating doesn't work, when the heater itself is set to a heating temperature below 20°C. So 20°C works, 19°C doesn't.
I have not found a parameter for minimal heating temperature, despite the one mentioned above, which i have set to -50°C.

Any suggestions?

Cheers, Patrick


  • edited December 2018
    as far as i can see heating is blocked below 20°C.

    see Extruder.cpp

            uint8_t output = 0;
            float error = act->targetTemperatureC - act->currentTemperatureC;
            if(act->targetTemperatureC < 20.0f) { // heating is off
                output = 0; // off is off, even if damping term wants a heat peak!

    maybe you have to modify a couple of points,this seems to be one. in my file it´s line 235,
    not shure if we use the same release.

  • Thanks! That did the trick.
    Sadly, i can only pass temperatures >=0 to the M104 command. But anyway, nice to know. Not sure why this option is not a parameter in the configuration file...
  • Original aim of firmware is FDM printing and that requires temperatures > 150°C,  so the low area is not of interest for this application. Also for same reason 0 is off.
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