Thermal Runaway  

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Durahl
(@durahl)
Eminent Member

Greetings!

I'm currently facing a problem with my MMU2S equipped i3 MK3S that is Thermal Runaway ( not Bed Thermal Runaway! ) related...

Since building the Kit, I've run through two Spools of Prusament PLA without issues though none of the parts printed so far have had a surface size like the Electronics Mounting Plate I'm building for a Tamiya 1:16 Gepard 1A2 Display Stand Model I'm converting into a Full-Option RC one:

With the Prusa provided Settings, the problem with these large parts usually manifests itself the second ( literally! ) the Part Cooling Fan kicks in while the second Bottom Layer is being laid out - Doing another part, I just witnessed the Hotend Temp rapidly falling from it's set 215°C and by the time I managed to change the Fan from 255 to 220/200 and reducing the Speed from 100% to 90% using the Printers Interface the temp had already dropped to 204°C thus barely above the threshold for another Thermal Runaway abortion ( AFAIK a 15°C difference ).

What problem am I looking at? Bad default Settings? Broken Hardware?
Where in PrusaSlicer can I find the Fan and Speed settings I keep dialing at the Printer itself? I'd like to make a specific profile to deal with such large parts.
Are there any other options on how I can deal with this issue?

Thanks in advance! =)

Posted : 04/10/2019 3:25 pm
nikolai.r
(@nikolai-r)
Noble Member

Here is what's happening:
Default PLA settings are pretty aggressive. First layer is being printed slow/no fan, but second layer is full speed. Means the heater block is being cooled by a fast filament extrusion and in addition part cooling fan starts to blow max power. In combination with with first layer set to 215C and second 205C, the heater turns off once second layer begins to print. So you have a steep fall in temp. Regular PID calibration is not sufficient for this case. PID control kicks too late in and not aggressive enough. The result is usually either -10C hopping or temp runaway error.

Solution:
Just put a silicone sock on the heat block: https://www.amazon.com/Genuine-E3D-Silicone-Sock-Original/dp/B077TKBKR3/

Other options are:

  • PID recalibration for more aggressive control
  • Reduce the speed
  • Reduce fan speed for second/third layer so PID control has more time to adjust
Posted : 04/10/2019 6:33 pm
bobstro liked
sam.d10
(@sam-d10)
Eminent Member

Just check that your heater cartridge is 40W if it is it should have a red cable if it is blue then it is a 30W which shouldn't come with the printer. Although this isn’t most likely the case you might as well just check to be sure.

Posted : 04/10/2019 7:31 pm
Karl Herbert
(@karl-herbert-g)
Estimable Member

Prusa i3 MK3S/MMU2S FFF-printer, Raspberry Pi 3B+, Octoprint; ISEL FB1 4-axis milling machine, Mach3, Benezan Electronics
Mein Motto: Bevor ich mich ufrech, isses mir libber egal!...
Posted : 05/10/2019 2:57 am
Karl Herbert
(@karl-herbert-g)
Estimable Member

https://forum.prusaprinters.org/forum/original-prusa-i3-mk3s-mk3-hardware-firmware-and-software-help/thermal-runaway-low-temp-extruder/#post-154674

Prusa i3 MK3S/MMU2S FFF-printer, Raspberry Pi 3B+, Octoprint; ISEL FB1 4-axis milling machine, Mach3, Benezan Electronics
Mein Motto: Bevor ich mich ufrech, isses mir libber egal!...
Posted : 05/10/2019 3:05 am
allen.m2
(@allen-m2)
Estimable Member
Posted by: @nikolai-r

Here is what's happening:
Default PLA settings are pretty aggressive. First layer is being printed slow/no fan, but second layer is full speed. Means the heater block is being cooled by a fast filament extrusion and in addition part cooling fan starts to blow max power. In combination with with first layer set to 215C and second 205C, the heater turns off once second layer begins to print. So you have a steep fall in temp. Regular PID calibration is not sufficient for this case. PID control kicks too late in and not aggressive enough. The result is usually either -10C hopping or temp runaway error.

Solution:
Just put a silicone sock on the heat block: https://www.amazon.com/Genuine-E3D-Silicone-Sock-Original/dp/B077TKBKR3/

Other options are:

  • PID recalibration for more aggressive control
  • Reduce the speed
  • Reduce fan speed for second/third layer so PID control has more time to adjust

Best explanation I have seen so far for what is happening.  In my case I just made the layer temps the same to stop it from shutting off the extruder heater.  It compensates for the added heat dissipation just fine this way for me.

Posted : 09/10/2019 5:09 pm
elizabethbrown2240
(@elizabethbrown2240)
New Member

hello,

which mechanism works here?

Have you ever try DIY it?

Posted : 12/10/2019 7:54 am
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