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Prusa i3 mk3s not keeping temp  

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NoobSquad1o1
(@noobsquad1o1)
New Member
Prusa i3 mk3s not keeping temp

A little while ago when I was printing a long part overnight it crashed saying thermal runaway I thought to myself "hmm odd but ok..." so I tried printing the part differently guessing the supports failed causing a glob of plastic to cause problems. When I started the second print it was on its 2nd layer and zipping around to fill in the 2nd layer when I noticed the temp which was supposed to be at 250 for petg dropped significantly to 235 there was a little amount of plastic on the hot end. Though I noticed a little got to the casing of the hot end wires. I was wondering what would be my first step diagnosing this to see what is wrong. That would be much appreciated and thank you for your time.

Posted : 07/11/2020 5:36 pm
karl-herbert
(@karl-herbert)
Illustrious Member
RE: Prusa i3 mk3s not keeping temp
Posted by: @oapryga

A little while ago when I was printing a long part overnight it crashed saying thermal runaway I thought to myself "hmm odd but ok..." so I tried printing the part differently guessing the supports failed causing a glob of plastic to cause problems. When I started the second print it was on its 2nd layer and zipping around to fill in the 2nd layer when I noticed the temp which was supposed to be at 250 for petg dropped significantly to 235 there was a little amount of plastic on the hot end. Though I noticed a little got to the casing of the hot end wires. I was wondering what would be my first step diagnosing this to see what is wrong. That would be much appreciated and thank you for your time.

Hello and welcome to the Prusaforum!

First I would check the thermistor, the associated leads and the connectors. The thermistor should have an internal resistance of about 100kohms at 25 degrees C. room temperature. With a multimeter you can check this easily and quickly.

https://help.prusa3d.com/en/article/thermal-runaway-temperature-drops_2131

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 : 07/11/2020 6:10 pm
NoobSquad1o1
(@noobsquad1o1)
New Member
Topic starter answered:
RE: Prusa i3 mk3s not keeping temp

@karl-herbert

When I checked the thermistor cable it read the proper 100kΩ resistance.

This post was modified 3 years ago by NoobSquad1o1
Posted : 07/11/2020 7:53 pm
karl-herbert
(@karl-herbert)
Illustrious Member
RE: Prusa i3 mk3s not keeping temp

@oapryga

It often happens that due to the numerous movements of the extruder the copper wires, especially if they are tinned, become brittle and fragile. Try moving the extruder back and forth while measuring the passage.

Another possibility would be to reduce the fanspeed. Even with too much air you can produce a thermal runaway. Alternatively you can also use a silicone sock.

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 : 07/11/2020 9:19 pm
Laura F Farrell
(@laura-f-farrell)
Trusted Member
RE: Prusa i3 mk3s not keeping temp

An issue I have come accross very occasionally is when the bed or hotend temp changes between layers - I think the firmware is set to allow a certain amount of time before it detects a 15C gap and triggers thermal runaway. The main issue for this I find is if its cold room and there is a lot of cold air. Close doors and windows and see if it replicates. 

Another suggestion is to run the temperature calibration again - this might help with your pritner's particular surroundings - Prusa give instructions for this at https://help.prusa3d.com/en/article/temperature-calibration_133266#:~:text=Navigate%20the%20LCD%2Dmenu%20to,sheet%20is%20on%20the%20bed.

 

Posted : 08/11/2020 2:28 pm
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