Print fan causes severe drop in hotend temp. Manually edit PID? Firmware issue?
Greetings all!
I have a HEAVILY modified MK3S that I recently added a BMG-M to and have been fighting a hotend heater issue where the temp falls off dramatically once the print fan starts. I have altered the firmware to allow the print to proceed without thermal runaway kicking in but it just ain't right. I have done multiple PID tune sessions and the attached pic is the best result I've been able to achieve. Only thing I can think is that the added heat sinking of filament being extruded is causing the extra cooling because my PID tune is done with the fan running at 100%.
I've run the PID tune with every combination of: fan off, fan on, bed hot, bed cold, chamber hot, chamber cold, extruder close to bed, and extruder far from bed.
I added the SKR and BMG at the same time. Already had the Mosquito running great in a Bunny (BNBSX) so I can't be sure if this related to the BMG or the firmware/SKR. This is my first attempt at a more-or-less from-scratch Marlin build so I very well could have set up something wrong....HOWEVER, I also tried an upgraded BMG cooling duct and it made the problem FAR worse. I never twitches until the fan turns off or on and is fine if the fan speed simply ramps up and down a bit (say, 30%-60%) so I know the print fan is putting too much air onto the heater block and/or nozzle and it can't react fast enough to a sudden change in blower speed.
Thoughts?
machine specs:
MK3S with full bear conversion
Moons .9 steppers on X&Y
Heated chamber using PID process controller, SSR, ducted fans, and Vulcan 250W AC strip heater
SKR 1.4 Turbo with custom firmware ported/based on Warcocki's work.
Remote mounted electronics
24v fans with higher-than-stock static pressure and CFM ratings
BMG-M with Mosquito Magnum, 50W heater, & Slice thermistor.
RE: Print fan causes severe drop in hotend temp. Manually edit PID? Firmware issue?
Greetings all!
I have a HEAVILY modified MK3S that I recently added a BMG-M to and have been fighting a hotend heater issue where the temp falls off dramatically once the print fan starts. I have altered the firmware to allow the print to proceed without thermal runaway kicking in but it just ain't right. I have done multiple PID tune sessions and the attached pic is the best result I've been able to achieve. Only thing I can think is that the added heat sinking of filament being extruded is causing the extra cooling because my PID tune is done with the fan running at 100%.
I've run the PID tune with every combination of: fan off, fan on, bed hot, bed cold, chamber hot, chamber cold, extruder close to bed, and extruder far from bed.
I added the SKR and BMG at the same time. Already had the Mosquito running great in a Bunny (BNBSX) so I can't be sure if this related to the BMG or the firmware/SKR. This is my first attempt at a more-or-less from-scratch Marlin build so I very well could have set up something wrong....HOWEVER, I also tried an upgraded BMG cooling duct and it made the problem FAR worse. I never twitches until the fan turns off or on and is fine if the fan speed simply ramps up and down a bit (say, 30%-60%) so I know the print fan is putting too much air onto the heater block and/or nozzle and it can't react fast enough to a sudden change in blower speed.
Thoughts?
machine specs:
MK3S with full bear conversion
Moons .9 steppers on X&Y
Heated chamber using PID process controller, SSR, ducted fans, and Vulcan 250W AC strip heater
SKR 1.4 Turbo with custom firmware ported/based on Warcocki's work.
Remote mounted electronics
24v fans with higher-than-stock static pressure and CFM ratings
BMG-M with Mosquito Magnum, 50W heater, & Slice thermistor.
With so many changes it is difficult to find an error via remote diagnosis. Prusa has tuned all components of the original model, including the air supply. With a 24V fan you have much more flow and I think you have to adjust there. The design of the fanshroud also plays an important role. For the time being an insulation of the heating block with silicone would be sufficient, because not the heating block but the nozzle area should be cooled.
In your graph I see a temperature drop of about 20 degrees C. I assume that this is caused by the fan, otherwise there is another error.
Statt zu klagen, dass wir nicht alles haben, was wir wollen, sollten wir lieber dankbar sein, dass wir nicht alles bekommen, was wir verdienen.
RE: Print fan causes severe drop in hotend temp. Manually edit PID? Firmware issue?
@karl-herbert
Correct, the pictured graph showing the approx 15c drop in temperature occurred at layer 2 when the print fan turned on (as intended) at approx 50% speed.
The graph is captured during a real print of a 200% scale benchy. PETG, .8mm nozzle, approx. 40mm/s, chamber temp of 50c...so the print fan is blowing 50c+ air. It doesn't exhibit this behavior during a PID tune under the same conditions. Only real variable is the addition of the extrudate.
I do have a silicone sock for the heater block but it tends to interfere with the cooling duct so I haven't had it installed in quite a while...since before getting the BMG. I'll see if I can get it to fit with the new extruder parts and report back.
- Thanks for your thoughts.