Ender 3 Pro weird reverse thermal runaway

[Conor Stewart]

I got some PETG filament to try on my Ender 3 Pro which I upgraded with a carbon steel nozzle and glass bed. It was printing fine but then at the same point (4 layers up) it was causing a thermal runaway. So I put it on again and watched the temperature, on the 4th layer the hotend temperature started to go down and I figured this was what was causing the thermal runaway since the temperature always seemed to be lower than it whould when the thermal runaway error happened. I managed to figure out what was causing the hotend to cool down and not be capable of staying at 230 C, it was because the part cooling fan came on at 100% after the 4th layer which cooled down the hotend too much and caused the thermal runaway error. It seems to be working fine now with the fan speed at 40%, just interested if anyone else has come across this problem. The hotend itself is supposed to be good for up to 280 C, I know the bowden tube is only up to 240 C, so why is this happenening, shouldnt the printer be designed to work fine up to its maximum temperature with cooling fans on and everything?

[dpc166]

I got some PETG filament to try on my Ender 3 Pro which I upgraded with a carbon steel nozzle and glass bed. It was printing fine but then at the same point (4 layers up) it was causing a thermal runaway. So I put it on again and watched the temperature, on the 4th layer the hotend temperature started to go down and I figured this was what was causing the thermal runaway since the temperature always seemed to be lower than it whould when the thermal runaway error happened. I managed to figure out what was causing the hotend to cool down and not be capable of staying at 230 C, it was because the part cooling fan came on at 100% after the 4th layer which cooled down the hotend too much and caused the thermal runaway error. It seems to be working fine now with the fan speed at 40%, just interested if anyone else has come across this problem. The hotend itself is supposed to be good for up to 280 C, I know the bowden tube is only up to 240 C, so why is this happenening, shouldnt the printer be designed to work fine up to its maximum temperature with cooling fans on and everything?

Hey there. I was doing a search online because I was having this same issue with my Ender 3 V2. I thought I had a bad thermistor so I replaced that and ran a test print. Had the thermal runaway error throw at the 4th layer. Went ahead to do the print and thought maybe the cooling fan was throwing too much and cooling the hot end. Noticed that when the fan started to fire up and especially at max speed, my hot end couldn't keep up. Thought this was strange since I've never changed any settings and after I started using PETG over 230C this became evident. I saw places saying you could replace the silicone sock, but I don't think that would do anything.

At this point I'm going to run a print for a new fan shroud to get the flow to the base of the nozzle and away from the heat block at about 30% fan speed (around 85 on the print screen whatever those units are) and then once I fit the new shroud to the unit, give it a shot at full speed.

Curious if you had any issues since.

[airscapes]

2 things;
PETG should need NO Cooling fan. Only time it is needed is if you are printing something tall and very thin.
If you place a hot end you need to run a PID on it so it will maintain the proper temp. This calibrates how the main board controls the power to the heater.
I can not tell you how to do it on your machine. Google your model and "Performing a PID calibrations "
Good luck

[dpc166]

2 things;
PETG should need NO Cooling fan. Only time it is needed is if you are printing something tall and very thin.
If you place a hot end you need to run a PID on it so it will maintain the proper temp. This calibrates how the main board controls the power to the heater.
I can not tell you how to do it on your machine. Google your model and "Performing a PID calibrations "
Good luck

Thanks! Did not know that you didn't need the cooling fan for PETG and when I replace with the sprite pro direct drive extruder next weekend, I'll certainly run all of the updates and calibrations I need.