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[Solved] Extruder temperature drops when the print fan kicks in  

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pcklbgr
(@pcklbgr)
Active Member
Extruder temperature drops when the print fan kicks in

I have finished my MK3S kit and I have this issue where as soon as it starts to print the second layer, i.e. the print fan kicks in - extruder temperature drops ~15° (for PLA specifically from 215° to 200°) and keeps going down from there and thermal runaway protection kicks in

I printed the benchy and Prusa logo (both gcode came with the kit) before it started to fail, so the issue either was not there from the beginning or the extruder temp recovers somehow in some cases. I have tried printing gcode generated by myself (with up to date PrusaSlicer), same thing happens.

What could be the cause for my issue? Faulty power supply? Some print fan alignment issue, where it blows cold air onto the extruder?

Napsal : 16/06/2019 3:53 pm
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(@)
Illustrious Member
RE: Extruder temperature drops when the print fan kicks in

Quite a few people have noticed this effect.  They started using the heater block silicon socks. 

Also, performing a nozzle PID calibration can help.

Napsal : 16/06/2019 6:46 pm
Dave Avery
(@dave-avery)
Honorable Member
RE: Extruder temperature drops when the print fan kicks in

also double check the cooling duct alignment - it should be pointing at the nozzle tip not the heating block

Napsal : 16/06/2019 7:45 pm
pcklbgr
(@pcklbgr)
Active Member
Topic starter answered:
RE: Extruder temperature drops when the print fan kicks in

I tried re-aligning the cooling duct, it now fases a bit downward (compared to a bit upward like it was before). And I also ran the PID calibration.

Neither seemed to help. Temperature still drops, a bit less it seems to around 203°.

It also seems to be somehow tied to the size of the models bottom, with smaller model temperature seems to stay at 203° (i stopped print before it got to a thermal runaway); with a bit larger model - temperature dropped a bit further, and I got another thermal runaway.

Napsal : 16/06/2019 9:47 pm
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(@)
Illustrious Member
RE: Extruder temperature drops when the print fan kicks in

The PID helps recovery; but the real cure is to insulate the heater block using the sock. The sock helps other things, too. So it's generally a good idea to use one.  

Your option is to find a better fan nozzle.

Napsal : 16/06/2019 11:06 pm
pcklbgr
(@pcklbgr)
Active Member
Topic starter answered:
RE: Extruder temperature drops when the print fan kicks in

The silicone sock arrived today (for whatever reason post took their time) - and it made all the difference. At worst it dropped to someting like 212-213 (it was printing PLA @215°), but it recovered shortly to 215° and was hovering around that.

Hopefully the PID callibration makes it even better.

Napsal : 05/07/2019 9:12 pm
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