Thurmal Runaway strange behavior  

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merrill.a
(@merrill-a)
Trusted Member

just did a 2.5 to 2.5S upgrade for new sensor. All calibrations went fine and setup was a breeze. So then I tried to do a print. 1st layer was great using PLA with a setting of 215/60. Then second layer started (.15) to .35mm. The extruder/bed temp shifted to 210/60 per normal. BUT the extruder temp then began dropping till it triggered a Thurmal Runaway shutdown. I sliced the same file on two computers and ran program on an SD card and using a USB cable using Prontoface. Same result each time. I also changed the nozzle temp after it stopped dropping but the drop continued. I then (without a print item) put the printer on 215/60 and it sat there stable as can be at a Z height of 100mm, 50mm and 1mm. Same for a 210/60 setting. I lowered the speed to 50%, closed off all room ventilation, but nothing worked. thought it might have been the computer controlling the print but it did the same with the SD card. Same goes for the slicer (2 computers same result). File has been printed numerous times on both a MK3S and this when it was just a MK2.5. The hot end is new, all components are tight. All check out OK. IT ALWAYS HAPPENS AT THE SAME POINT, just after it shifts to the lower temp for second layer print. Yes I did slice for the new MK2.5S. I don't have the slighist idea where o go from here.

Note: all firmware and software was just updated for both printers and computers.

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Posted : 07/07/2020 1:16 am
merrill.a
(@merrill-a)
Trusted Member

Let me add that I just sliced the same file and am printing it on my MK3S. When it went to the second layer, from 215/60 to 210/60, the temp dropped below 200 but recovered shortly afterwards. So a similar problem but maybe the 24 V MK3S using 24V made the recovery possible. I know that is grabbing at straws but it is what it is.

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Posted : 07/07/2020 2:55 am
merrill.a
(@merrill-a)
Trusted Member

Update: size of print (LxW) does not matter. First layer prints fine. Tried printing with FW 3.8.0, 3.8.1, 3.9.0 with same results. Printed at .20 layer height, same problem. Changed extruder temp in second layer to be the same as first, same results. Changed print speed, same.

Attached is a picture of the 3 FW prints, They were printed using Prontoface and that is why there is a runout after the thermal runaway point (note also a layer shift as Prontoface went to "cold extrusion prevented" mode.

I used the streight Gcode Prusa "Prusa 200um 30M" file to eliminate the slicer and got same results.

Example as to what happens (same when first layer is 215/55 and subsequent layers are 210/55 or when I have set slicer to 215/55 first layer and 215/55 all subsequent layers): 1st layer rock solid on target temp; as soon as 2nd layer started the temp immediately dropped and continue to drop to around 201/55, climbed back up to 202-203 for a few seconds and then began to drop and reached thermal runaway at about 192/55.

I actually reached the 3rd layer on one print but just barely before thermal

If I just let the printer set at any given temperature (not printing) it stays rock solid.

I think the above testing has eliminated all external software as being a problem and since I used 3 different versions of the FW and obtained the same results, it is most likely NOT the firmware.

I am at a dead-end as to what the problem might be or what to check. Just having a failure when it shifts to the second layer is very strange to me.

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Posted : 08/07/2020 1:34 am
merrill.a
(@merrill-a)
Trusted Member

Update: Reflashed the latest FW. Decided to try to do a pause when the printer went to layer 2 and see what happens.

1. layer 1 printed OK with temp at 215/215. Layer 2 started and should have gone to 210/210 but kept dropping past 210 as it had done before. At 195 I paused the print and the printer showed 195/0 with a bed of 55/55. waited a minute or so and then did a restart. The temp had dropped to 185 but slowly showed a recovery back to 203/210 and started to print. Again the temp started dropping. I repeated this a few times and got the same results. BUT NOTICED that when the print restarted it started printing at a point it would have been at had it not stopped (appears that the gcode kept running). The longer the pause, the wider the missed part of the print.

2. went under settings and found the temperature calibration off so I turned it on. 1st layer printed ok with stable temp. Went to layer 2 and the bed temp dropped past the 210 settings point and kept dropping until I paused it at about 190. the target temperature changed, again, from 210 to 0. the temp kept dropping and I resumed at about 183. The target temp went back to 210 and the extruder temp slowly climbed back, this time to 209, and started printing. Temp immediately started dropping again and the same printing gaps were evident again. I did this multiple times, even getting to layer 3 by pause/restart, pause/restart repeated with same results.

Note: I have also checked all the wiring to the main board and found all ok.

Due to a possible main board problem some months back, I replaced the main board. The printer worked fine until I made the 2.5S new filament change. Cannot think of any reason that sensor or cable could be the problem.

If I come up with any new ideas, I will post them. I hope someone reads this and has some ideas as to what I might try or what the problem might be.

AGAIN: I can set the temperature of the printer and the Z height at various settings and the temperature stays stable. the problem only appears when the printer starts to print layer 2 and above.

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Posted : 12/07/2020 8:16 pm
Karl Herbert
(@karl-herbert)
Famed Member

@merrill-a

Thermal Runaway indicates a problem with the thermistor or too much cooling, loose contact or corroded thermistor connection. Pidtuning can help in such cases. A too high frontfan speed can also cool the nozzle down too much. In this case a silicone sock can help. I think, that has nothing to do with the firmware.

Statt zu klagen, dass wir nicht alles haben, was wir wollen, sollten wir lieber dankbar sein, dass wir nicht alles bekommen, was wir verdienen....
Posted : 12/07/2020 8:40 pm
keri7240
(@keri7240)
Active Member

I had the same think happen when I upgraded from MK2s to MK2.5s.  Installing an E3D plated copper heat block seemed to make it worse.

It seems to only happen with PLA prints as the fan goes to high speed on the 2nd layer... the hotend temperature plummets from 210C to maybe 190C then starts to recover slightly.  Sometimes it very slowly recovers to 205-210C, sometimes thermal runaway protection kicks in.

An E3D silicone hotend sock cured it. With the sock, the temperature drops only a few degrees and recovers rapidly.

Looking at the MK2.5s/3s  fan duct, it blows a lot of air against the the heat block right where the thermistor is located, so this behavior is not surprising.

A search of Thingiverse reveals some modified fan ducts to resolve this issue. Might be a better solution than the silicone sock.

 

 

¡no entiendo Español!
Nein! Nicht Versteh!
Я немного говорю по-русски но не очень хорошо, и...
I'm not very good at English either! Maybe someday I'll find a language I'm good at?...
Posted : 13/07/2020 1:24 am
merrill.a
(@merrill-a)
Trusted Member

Couple of things:

1. the sock worked. I did install an E3D plated copper heat block. I don't know why I never thought to slow down the fan speed but the sock works great. It dropped to 207 and stopped then recovered.

2. I still do not understand why, when I paused the print, when I started it again it did not start where it had stopped but, according to how long it was paused, it started downstream from different distances. Like the gcode kept running. If anyone has an idea about that, I would like to hear about it.

3. I am sure Prusa must have known about this problem and maybe put out a note about it (maybe they did and I just missed it) as they are usually very good with such things.

I appreciate the feedback as I was really getting frustrated trying to figure this out. I would rather use the sock than change out the fan vent to fix the problem.

 

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Posted : 13/07/2020 5:04 am
keri7240
(@keri7240)
Active Member

I found it!

After another week or so, the Thermal Runaway started to recur, then the heater just died altogether.

My Thermal Runaway ended up being a bad crimp on the genuine E3D heater wiring, about 2cm from the heater cartridge itself. Replacing the heater cartridge fixed it and the PRUSA now works great without a sock.

Details in this thread:

https://forum.prusaprinters.org/forum/original-prusa-i3-mk2.5s-mk2.5-hardware-firmware-and-software-help/mk2-to-mk2-5s-upgrade-thermal-runaway-problems/#post-235054

 

¡no entiendo Español!
Nein! Nicht Versteh!
Я немного говорю по-русски но не очень хорошо, и...
I'm not very good at English either! Maybe someday I'll find a language I'm good at?...
Posted : 26/07/2020 9:18 pm
Karl Herbert
(@karl-herbert)
Famed Member

@keri7240

I'm glad you were able to find the error. As so often, the cause is usually to be found in hidden errors in the hardware.

happy printing!

Statt zu klagen, dass wir nicht alles haben, was wir wollen, sollten wir lieber dankbar sein, dass wir nicht alles bekommen, was wir verdienen....
Posted : 26/07/2020 10:19 pm
merrill.a
(@merrill-a)
Trusted Member

I measured the ohms and it read 3.6 so no problem with the hot end. So back to the fan ducting.

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Posted : 28/07/2020 12:27 am
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