Prusa Slicer PLA print fan speed causes Thermal runaway  

RE: Prusa Slicer PLA print fan speed causes Thermal runaway

same question here!

RE: Prusa Slicer PLA print fan speed causes Thermal runaway

Unfortunately, Prusa's fan shroud is not designed to direct the air to the right point. The Prusa S shroud is simply just an extension of the fan outlet.
A silicone sock on the heat block solves the problem, or you can mount another type of fan shroud that controls the air flow better.

https://www.thingiverse.com/RH_Dreambox/designs

RE: Prusa Slicer PLA print fan speed causes Thermal runaway

I think the current fan duct is poor.  It does create a huge amount of air flow but it tends to just wash over everything. 

I have my own design that I use which has 3 relatively small openings that are quite close to the nozzle and are designed to direct that air straight at the tip of the nozzle where the cooling needs to be.  Because of the design it also allows me to reduce the fan speeds but still have better cooling than the original.

I could not print higher temp filaments very well with the standard fan duct although It does work fairly well with PLA if you can avoid thermal runaway.  I would recommend turning up the voltage on your PSU as it creates a faster heat up time and should help with your thermal runaway issues.  I've got mine turned up to 13.3V although I have heard people running higher than this.  I'm assuming you have the 12V PSU as you have the MK2.5S.

RE: Prusa Slicer PLA print fan speed causes Thermal runaway

Posted by: @philip-b4

I've just updated my MK2.5 MMU2 to a MK2.5S MMU2S. Part of this was rebuilding the extruder and adding a new fan duct provided by Prusa for free (thanks guys!)

Printing PETG was fine, but as soon as I decided to try PLA I ran in to the dreaded Thermal Runaway problem. It was pretty obvious from the start that this was to do with the print fan. First layer was fine but as soon as the 2nd layer started the fan came on like a tornado and the hot end temp dropped 20 degrees where it remained. Thermal Runaway was soon to follow. I went about rechecking everything but ultimate came to the conclusion that the new fan ducting is blowing a lot more air at the print and some of this is making its way to the hot end. By dropping the tune menu fan speed down to 100 I was able to get past the problem. Do the Slicer profiles need changing maybe? Does anyone from Prusa care to comment?

Each filament responds differently to the air supply. Some don't need air at all. You can set this in the PrusaSlicer for every situation. Try to run pidtuning, reduce fanspeed or use E3D silicone socks.

RE: Prusa Slicer PLA print fan speed causes Thermal runaway

Can't wait to try this.  Thanks for sharing the solution.