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[Solved] Hotend temperature unstable  

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Jiheffe
(@jiheffe)
Eminent Member
Hotend temperature unstable

Hi,

After a couple of small printys this morning, I switched off my i3 Mk3S and turned it 180° in order to mount this enclosure for a Rastberry Pi. I placed it back, removed the PETG and loaded PLA, and switched the textured plate for a smooth. I also took the opportunity to place a LED ribbon on the frame.

Put the printer back in its normal position, and loadeda small calibration *.gcode to check the life-Z. Now, the hotend temperature will not stabilize ar 215° C but goes in cycles between abour 185° and 230°... See graph below:

I shut down and restarted the printer, restarted Octoprint, to no avail. I disconnected the Pi with Octoprint just in case, but no change.

Could it be that by turning the printer around, the thermistor connector got loose on the Einsy board?

Posted : 06/06/2020 4:07 pm
Neophyl
(@neophyl)
Famed Member
RE: Hotend temperature unstable

Are you taking power from the printer to power the led strip or ?  You might also want to run the pid process for the extruder heater. 

Posted : 06/06/2020 4:20 pm
Jiheffe liked
Jiheffe
(@jiheffe)
Eminent Member
Topic starter answered:
RE: Hotend temperature unstable

@neophyl

Hi,

No, both the Pi and the strips are on their own power supplies. Will do the PID.

I looked into the Einsy for any loose connextion but all seemed OK.

Posted : 06/06/2020 4:35 pm
Jiheffe
(@jiheffe)
Eminent Member
Topic starter answered:
RE: Hotend temperature unstable

Update:

Started a PID calibration, it stopped immediately after 1 second. Started again, after 10-20 seonds I a message "M112 called. Emergency stop", Octoprint reported a "HOTEND THERMAL RUNAWAY"...

I have a spare thermistor. Guess this would be the time get it out?

 

Posted : 06/06/2020 4:45 pm
karl-herbert
(@karl-herbert)
Illustrious Member
RE: Hotend temperature unstable

@jiheffe

With such large deviations, you are almost certain to have a loose contact on the thermistor or on the heating cartridge. This is noticeable when the printer is in motion. A wire may also be squeezed. I would check and meassure these wires.

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 : 06/06/2020 7:06 pm
Jiheffe liked
Jiheffe
(@jiheffe)
Eminent Member
Topic starter answered:
RE: Hotend temperature unstable

Update 2:

1/ Wife called for dinner 😎 

2/ Back to the printer, started a preheat at PLA temperature -> Resulted once again in thermal runaway...

3/ Removed and reinserted the hotend thermistor (ditched the blue E3D sock)

4/ Successfully did a test print of a 50x50x0.2 mm calibration square

5/ Ran PID calibration -> success

6/ Now happily printing again

Could it be the thermistor had a problem? Note I didn't replace it. Just removed from the heatblock and reinserted it.

Posted : 06/06/2020 7:08 pm
karl-herbert
(@karl-herbert)
Illustrious Member
RE: Hotend temperature unstable

@jiheffe

It's good to see the printer up and running again. Possibly there was a short circuit. Loose contacts, and short circuits are a common cause of such problems. Another possibility would be a too high fan speed, which then cools the nozzle down too much (in this case you could use a silicone sock or reduce the fanspeed). If the pidtuning is not optimal, the temperature deviation is only a few degrees C.

I would still do the pidtuning e.g. at 240/90 degrees (PETG) with running nozzlefan (see Slicersettings for the fanspeed): https://mattshub.com/blog/2017/04/26/pid-tuning

 

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 : 06/06/2020 7:48 pm
Jiheffe liked
Jiheffe
(@jiheffe)
Eminent Member
Topic starter answered:
RE: Hotend temperature unstable
Posted by: @karl-herbert

I would still do the pidtuning e.g. at 240/90 degrees (PETG) with running nozzlefan (see Slicersettings for the fanspeed): https://mattshub.com/blog/2017/04/26/pid-tuning

 

Thnx! Will do.

 

JF

Posted : 06/06/2020 8:01 pm
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