blueeagle69
commented
5 years ago I do believe I have the same issue. I was printing at 240° just fine. The fan came on and my nozzle temp drop so low it triggered thermal projection and stopped the printer. I rolled back to a previous build and dropped the temp to 230° so I could get the print done. I am now back on the build which is around 4 days old, but haven't printed again since. My build in question was downloaded and flashed when the LPC176x updates were added. I will have to test 240° with fan again I think. I've added a sock for good measure.
boelle
VanessaE
bandoned
Patag
thinkyhead
ManuelMcLure
github-actions[bot]
This is Marlin bugfix-2.0.x branch, commit 61225e68, running on an SKR v1.3.
Description
For a while, I've been having problems with my hotend staying... well... hot. At the beginning of a print, it would maintain its target temperature just fine, but when the print would get to the point where the layer fan turns on, the hotend temperature would drop by several degrees, and often fail to recover. This has forced me to relax the hotend thermal runaway setting a bit (it should still be safe, though, just not ideal).
Such was the case for a print I was doing today. It just didn't want to heat back up once the fan kicked-in.
My layer fan is aimed just below the nozzle, and like almost all layer fans/ducts, the outlet blows a bit onto the nozzle and the bottom of the hotend. Naturally I assumed that this was the issue, so I made a simple "air dam" to put between the fan duct and the bottom of the hotend, blocking the airflow from reaching all but the lowest few millimeters of the nozzle itself.
I ran a second attempt at that print (same g-code), but the air dam didn't seem to do any good; after around half an hour of printing, the hotend temperature had dropped from its target of 230° down to 220°, with heater PWM holding at 127 (or so it said), and with the fan at only 25%.
With that second print still going, I told Pronterface to bump the hotend temperature up to 240°, just to see what would happen, then "came to my senses" after a few seconds, and turned it back down to 230° -- surely it has no hope of getting to 240° anyway, right?
Here's where it gets weird: when I turned the temperature target up and back down, the reported hotend temperature began to rise, and the reported PWM value began to drop. Within maybe 30 seconds, it had stabilized at 230°, and PWM was hovering close to 100. That's right where it was supposed to be to begin with, so it's not like fiddling with the temperature like that should have done anything; it was as if the heater/PID code got "stuck" somehow. I did not notice if it was the initial act of raising the target temperature that did it, or the seconds-later act of lowering it.
As of submitting this issue, that second print has been going completely normally for about three and a half hours, with the temperature remaining as stable as I would expect (within one degree). The print speed, fan speed, flow rate, linear feed rates, enclosure temperature, bed temperature, room temperature, etc. have all remained steady this whole time - that is, the conditions of the printer and its surroundings were the same when the hotend temperature corrected itself as when the fan switched on early in the print, Z position aside. UPDATE: the print completed without incident, and the temperature remained steady for the remainder of the time that I was around to watch it.
Steps to Reproduce
Observe as the hotend temperature corrects itself.
Logically, turning the temperature up and then right back down should have had no effect.
You may need to do this on a 12v machine (and hence 40W heater cartridge), since that's what I use.
Expected behavior: If there's more power to be had, and it's needed, the heater should heat up. :-)
Actual behavior: Something gets confused the hotend stops trying to heat up. :-)
Additional Information
Configuration.h
```c++ /** * Marlin 3D Printer Firmware * Copyright (c) 2019 MarlinFirmware [https://github.com/MarlinFirmware/Marlin] * * Based on Sprinter and grbl. * Copyright (c) 2011 Camiel Gubbels / Erik van der Zalm * * This program is free software: you can redistribute it and/or modify * it under the terms of the GNU General Public License as published by * the Free Software Foundation, either version 3 of the License, or * (at your option) any later version. * * This program is distributed in the hope that it will be useful, * but WITHOUT ANY WARRANTY; without even the implied warranty of * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the * GNU General Public License for more details. * * You should have received a copy of the GNU General Public License * along with this program. If not, seeConfiguration_adv.h
```c++ /** * Marlin 3D Printer Firmware * Copyright (c) 2019 MarlinFirmware [https://github.com/MarlinFirmware/Marlin] * * Based on Sprinter and grbl. * Copyright (c) 2011 Camiel Gubbels / Erik van der Zalm * * This program is free software: you can redistribute it and/or modify * it under the terms of the GNU General Public License as published by * the Free Software Foundation, either version 3 of the License, or * (at your option) any later version. * * This program is distributed in the hope that it will be useful, * but WITHOUT ANY WARRANTY; without even the implied warranty of * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the * GNU General Public License for more details. * * You should have received a copy of the GNU General Public License * along with this program. If not, see(Above configs, as a Zip: Marlin-configs-2019-11-05.zip )