Issue after autotune 303. Temp drops big time when fans kick in.

Hello, Machine is Rostock Max V2 (Rambo board) HE280 Hot end upgrade. Used to work fine ish (hotend consistently running 5 degrees lower than set). I ran it like this for 2 years.

Ran autotune M303 P0 S235 x0. Didn't seem correct. Than I ran M303 P0 S90 x0 and it seemed perfect.

210 Degrees maintains great within a degree or 2 ... UNTIL the the fans kick in. Then the temp keeps dropping to less than 190 until hardware reports a fault and the print is stopped. It appears that heaters are full on and trying to keep up. (led light solid on RAMBO)

PID Incorrect? Heaters just not keeping up? Fans blowing too much air on nozzle? Should I install a Silicone sleeve on the hot-end?

Any help is much appreciated!

- A.J.


  • Check in a host software if output is 100%. If it is full power the heater is not able to keep the temperature and PID is not relevant. The fans controlled with M106/M107 should only cool filament and not the extruder it self. If that happens you get a drop when they kick in until the extra cooling is compensated - but only if extruder can do so. Some extruders need a cooling for the break to the upper part to prevent fluid filament from creeping up. These fans kick in at some temperature like 50°C.

    To solve your problem you need either more power or less cooling. Problem is that every extruder needs a special temperature distribution to work. So yes, you can isolate bottom part so filament blower does not hit the heater block. That is normally ok. But as soon as it gets too much heat fluid can walk up and that will cause extruder to jam. Actually that is why jams happen. So you need to keep inside limits of the extruder. I don't have this one so can not say how hard that is. Maybe it is also just the heat cartridge that is not getting that hot any more or has not the good contact to the metal it should have.
  • Thank you for your response! I am unsure how to check the output power of the heater. There is a separate fan to cool the heat break. After reading your message and doing a few prints at 50% fan MAX, I suspect that the fans are trying to cool the nozzle and/ or the lower heat block itself. The heating element could also be the issue as you suggest. Getting tired or bad physical or electrical contact.

    I ran a print with zero fans at 230 degrees and it maintained temperature very well in my opinion.
  • At least if no fan allows higher temperatures you see that it adds to cooling heater block. So adjusting speed or where it cools might already help here. Output power P = U * I with I = U/R so P = U^2/R so you just need to know voltage and heater resistance.
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