Thermal Runaway  

Re: Thermal Runaway

hmm I just noticed in another Print that it's not only the fan. Even on infills with temperatures around 255°C the temperature drops around 10°C. Without the fan even beeing on. This is strange.

Does anyone else notice this?

Re: Thermal Runaway

Apart from any issues with the thermistor (unreliable wires for example), are you perhaps printing in a very cold room, or a room with a significant airflow?

Re: Thermal Runaway

Have you had a look at the help guide for thei: http://help.prusa3d.com/mk2-electronics/thermal-runaway-and-temperature-drops?from_search=14015845

Peter

Re: Thermal Runaway

@jeroen.b no, roomt temperature is quite normal (~21°C)

@PJR i didn't know that page, quite some helpful information. Will especially check for the connector which could be the problem as I keep seeing this problem from time to time and it's gone again afterwards.

Re: Thermal Runaway

I saw this problem after replacing the 0.4mm nozzle with a 0.8mm nozzle. I saw the temp drop from 240 to 228 [PET] on the second print attempt when I was observing. Decreasing the print speed (live) allowed the temp to rise to 231, but not higher. I'm testing the same print with a 0.6mm nozzle now.

Re: Thermal Runaway

Printing with 0.6mm showed the same behavior. I switched back to 0.4mm and it's printing fine now.

Re: Thermal Runaway

I changed from 0.4 to 0.8 and am also getting this now.
Should not be like this though?

Re: Thermal Runaway

I wouldn't think this is desired behavior but may be normal.

Looking through the firmware source if the current temperature is 10 degrees less than the target temperature the power output should go to max. I re-ran autoPID and compiled my own copy of 3.0.9 to make sure the source matched the firmware I was testing against. Adjusting PID didn't make any difference, nor did using the firmware I compiled.

I ran out of time searching the Firmware for where the MAX power output is defined for the heaters. I may be looking for something that doesn't exist as I'm coming to the Rambo from Smoothie and may be conflating some configuration options between the two in my head.

I suspect the RamboMini may not be able to output enough power to keep the hotend at temp with the larger nozzle sizes due to the increased heat loss resulting from the increased material flow rate. I'm hoping I'm mistaken and am just missing something somewhere which is entirely possible.

Re: Thermal Runaway

I do not have a solution, but I am having a thermal runaway problem too. I am printing a large object and I tried to put it on Fast quality in Slicr. Last night the print failed due to thermal runaway. I thought it might because the room is cold, but I tried it again today with the heat on and it failed again.
What I discovered was when the nozzle was over the print, the temperature went down. When the nozzle was not touching the print it went back up. (See the video below)

3 things I will try next:
Change the print from Fast to Normal quality
Try a different file, maybe this object is not good!
Check the thermistor

https://goo.gl/photos/LnNt33xvPoh1aB7C7

Re: Thermal Runaway

Keri,

I wonder if the part cooling fan is blowing too fast and cooling the hotend.

I noticed when I was printing with the 0.6mm nozzle that as soon as I stopped the print job the temperature shot up. Coupled with your results I now suspect the part cooling fan is turned off immediately when stopping a print from the menu and with the heater power on full it shoots up briefly.

I wonder if decreasing the part cooling fan speed would help with the issues we've been seeing.

Re: Thermal Runaway

My printer runs at 40% fan, with PLA, to prevent thermal runaway...

(I also increased the 12volt output from the power supply, a little. (think it's 12.5 volts now... )

regards Joan.

Re: Thermal Runaway

James,

Thinking about what you said made me realize that my printer might have opposite of thermal runaway. What I mean by that is when the nozzle (which is the stock one btw) is over the print it loses heat quickly. When it is not over the print it goes to 215 and does not go higher. I assume it gets the thermal runaway because it thinks there is something touching it and conducting heat away from it. I've had this when I put a wrench or something on the nozzle.

It might be the location of the fan in regards to this one particular print which is supposed to be a tree, and it fails on the trunk. Other files print fine.

I will try to decrease the fan speed and see what happens
Thanks!

Re: Thermal Runaway

I reduced the speed of the part cooling fan to 30 from 50 and now am able to print with the 0.6mm nozzle without issue.

Re: Thermal Runaway

I am getting thermal runaway print failures for the first time now.

It is due to 230C nozzle temp set. I have printed many times at this temperature without issues, including the fan running, but what I changed is that I am this time printing with layer height 0.35mm FAST setting.

Observing the nozzle temperature during the print makes it obvious that the high rate of filament extrusion during some parts of the print causes the nozzle to cool down gradually until the 'Thermal runaway' error is triggered.

I reduced the fan speed to 150 / 255 live during the first part of the objects, then set temp to 60% in Slic3r (153/255) for the next part. However, I still get the thermal runaway error at reduced print speed.

What surprised me is that when I reduced the nozzle temp (live) to 220C, the 'THERMAL RUNAWAY' happened nevertheless, although the nozzle temp was 218C at the time it happened.

Re: Thermal Runaway

I had this issue before too. I think the issue is caused by the cooling fan is too powerful. If printing at high nozzle temp for PETG for instance, there's a high chance that you will run into the issue even at 40% fan speed. To resolve it, I bought the E3D silicon sock and it solves the issue even running at 100% fan speed.