Thermal Runaway
I'm trying to print a large piece (a sandal for my foot) and my print aborts in a repeatable place.
I've printed with PLA and PETG for years and have never seen the THERMAL RUNAWAY error. This week, I switched to a FLEX filament to print my sandal. I printed a smaller piece (iPhone case, 4+ hours) successfully. But my sandal has failed three times on the first non-solid layer, 1.2mm from the print plate.
I saw in the Thermal Runaway (i3 series) | Prusa Knowledge Base page that the MK2.5S may need slower fan speed for PLA. Could something similar be true for my FLEX situation? Does anyone have any thoughts about what could be causing this?
RE:
Update... I'm experimenting with filament nozzle temperature. PLA is 215º for 1st layer, and 210º for other layers. FLEX is 240º for both. I've never had a THERMAL RUNAWAY error for PLA in 8 years. So, I tried 215º first.
At 215º and 220º, I saw a feed error for my FLEX filament. I'm seeing the THERMAL RUNAWAY error early in the print when running my nozzle at 240º and at 230º. I'm now running at 225º and so far, so good.
I did see the temperature readout on the printer dropping as low as 210º and rising as high as 220º. I hypothesize that the THERMAL RUNAWAY error occurs when the nozzle drops too low or rises too high to compensate for a low drop.
I've positioned a video camera in front of my printer's readout so I can capture the phenomenon.
RE: Thermal Runaway
My 225º run has failed. I see the nozzle temperature dropped to 209º, rebounded to 210º, then back to 209º, then after 10 seconds, the THEMAL RUNAWAY error presented.
Why is the temperature 15º below the prescribed temperature of 225º ?
How can I enforce a consistent temperature (for example, 220º +/- 5º) for the duration of my print? I've see suggestions about adding color layers to re-establish temperature but will this guarantee the nozzle remains on target? I would think that 15º variance would be undesirable from a design point of view.
All suggestions welcome... 🙂
RE: Thermal Runaway
I've enabled the Temperature Chamber and set the temps and to 240º nominal and 235º minimal. The nozzle temp readout looked good for a few minutes and then steadily declined to 217º to produce the THERMAL RUNAWAY error.
RE:
Peer Review Requested:
As I understand the conditions for the THERMAL RUNAWAY error, I consider the following scenario:
- target nozzle temp = 240ºC
- thermistor reports 240ºC
- nozzle assembly expands due to thermal expansion
- thermistor comes loose
- thermistor reports 224ºC
- after 45 seconds, Prusa firmware aborts print to prevent excessive heating of elements
The trouble I'm having with all of this is that I have printed PLA successfully for 8 years and PETG successfully during COVID-19 with no THERMAL RUNAWAY errors. Could my nozzle assembly have changed/degraded over time to produce a loose component situation?