Thermal runaway with cooling fan
Hi,
I've read through a few of the other threads about this issue, but most seem to be caused by wiring issues with connection issues to the thermister or heater cartridge causing it to drop the signal, or a change to the cooling duct. My issue is that the minute the cooling fan kicks in the hot end temp plummets and cannot regain. Knocking the fan down to under 180 allows the temp to stabalise. I've checked wiring, heater cartridge clamp, thermistor positioning and fan duct. Everything looks fine. I'm printing PLA and the bed temperatures seem fine, it's just the hot end.
While it's a bit cold at the moment, the printer is in an enclosure, and up until a couple of months ago was printing fine (with colder weather). The printer hasn't been moved or changed since it's developed this issue, so it's a bit odd. I've tried warming the room with a fan heater, which I've never had to do before.
RE: Thermal runaway with cooling fan
Welcome here in the Prusaforum!
I think all is ok with your hotend. Try to use a silicone sock to reduce the heaterblock cooling https://e3d-online.com/v6-silicone-socks-pack-of-3 or reduce the fanspeed.
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: Thermal runaway with cooling fan
I'll give one a go, it's just odd that it's started happening now when it's been fine before. My other 6 year old I3 based printer also runs an original E3D hot end (at 12v) and I've never had issues with temperature even with aggressive cooling.
RE: Thermal runaway with cooling fan
The silicone sock will make all the difference.
RE: Thermal runaway with cooling fan
I've done a bit more digging, and while a sock might help, there's definitely an issue here.
I've pointed a fan heater directly into the enclosure and left it for a couple of hours prior to starting a print.
The temperature inside the enclosure is 44 degrees celsius, yet the print still failed even with the fan turned down to 180. I had to drop to 150 when I reprinted the model to allow it to recover the temperature.
RE: Thermal runaway with cooling fan
Can you check your power supply voptage.
And can you check the wiring to hee heater for hot spots when the printer is heating.
Low voltage and cable damage can both cause this problem
Both can develop with time...
Regards joan
I try to make safe suggestions,You should understand the context and ensure you are happy that they are safe before attempting to apply my suggestions, what you do, is YOUR responsibility. Location Halifax UK
RE: Thermal runaway with cooling fan
Bit of an update. I've checked the wiring again for visible damage and also tested the resistance of the heater cartridge.
The cartridge is 15.3 ohm which isn't too far from the quoted 14.4 (I'm assuming a tolerance of 10%)
Voltages are pretty stable at just over 23v. Heater voltages are steady until up to temp then drop (or at least look like they do on a conventional volt meter) to around 5-9v while maintaining hot end temp. When the fans kick in this jumps back to 23v but the hot end never manages to return to full temp and errors on thermal runaway.
No noticeable hot sports, but it's hard to tell with the sheathed cable and I don't have a thermal camera to hand.
I've temporarily resolved the issue by mostly blocking the front port on the cooling vent so that the fan does not blow against the cooling block and most of the air is directed to the sides and downwards. Not ideal, but it's working for now.
The printer's only 9 months old and not heavily used so I'd be surprised if it's something that's due to use/age unless a component had an underlying fault.
My old Prusa i3 is almost 6 now and has one of the first E3d V6 hot ends still running strong with it's original heater cartridge .... it's on it's 4th tip and 3rd fan mind 😉
I may try swapping the cartridge out as it's cheaper than the PSU at some point if things get worse, or if I notice much difference with the partially blocked duct.
RE: Thermal runaway with cooling fan
Finally had time to check the printer over.
This looks like it's a faulty thermistor cartridge in the hot end. Slightly annoyed I didn't check it earlier, but as it was quite cold the temps didn't look too far out, now the weather has warmed up you could see a large difference between the reported hot end temp and the bed temp after the printer has been off all night. Bed is showing 17 degrees, hot end 6, so 11 degrees difference.
I had checked the thermistor wires for damage, but I've now removed it and tested the resistance. It's showing 450k at around 20 degrees. Strangely I'd have thought that would show as about -5 not 7 degrees.
I've never had a thermistor fail in such an odd way, but it's definitely not well and needs replacing.
RE: Thermal runaway with cooling fan
@ed-2
450k at 20 degrees C. is definitely too much (should have about 127k). You should replace the thermistor. Here is a table:
Temperaturtabelle für Thermistor Semitec 104GT
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: Thermal runaway with cooling fan
I have had the same issue since upgrading the firmware, I have tried the PID auto tunning but this does not help as the thermal shock of the fan starting is to great. The problem only happens when using Slic3r and not Cura which ramps the fan speed upto 100%.
This is a know issue https://github.com/slic3r/Slic3r/issues/3366