Changed Extruder thermistor, now lots of stringing as if printing too hot
Hello, I own an MK2s and recently my extruder thermistor cable got damaged beyond repair after a year and a half of use. The best replacement I could find locally was this: https://filament2print.com/gb/spares-extras/825-cartucho-termistor-e3d-original.html. Which according to the datasheet is a 100k ohm thermistor.
After installing it I did a few test prints, and everything seemed ok. But then I started to notice a LOT more stringing than before, and a lower print quality. Also, when preheating or idling the nozzle appears to lightly smoke and there is a caramel smell (which I head some people smelled with hot PLA, but I never did before). It's not a bad or electrical smoke, it feels more like the end of a soldering iron. I tried the PID calibration but it doesn't seem to have changed anything. It feels as if the nozzle is heating up more than before.
I'm attaching two pictures, the better looking one is from before the thermistor change. The only thing that has changed between prints is the thermistor (same gcode file, same black PLA spool). I never did any stringing cleaning to the original part, that's how it came out (I did remove the supports at the top, but they didn't have strings like the new one.
TLDR: My extruder thermistor broke, I replaced it with a non Prusa one and now there is a lot of stringing and bad print quality. Feels like the nozzle is printing too hot. Has this happened to anyone else? Is there any calibration needed if the new thermistor does not have the same resistance values as the original one?
RE: Changed Extruder thermistor, now lots of stringing as if printing too hot
Posting imgur link for convenience: https://imgur.com/a/ColrnUq
RE: Changed Extruder thermistor, now lots of stringing as if printing too hot
And I just thought to run selftest, and it says error: "Heater/Thermistor - Not connected".
I checked that the thermistor cables are correctly connected, and the nozzle does heat up to 215 (or so the display says). But selftest fails.
EDIT: Although I remember that this was also the case before the thermistor change. I always assumed it was due to this: https://forum.prusa3d.com/forum/original-prusa-i3-mk2-s-others-archive/selftest-error-heater-thermistor-not-connected/
RE: Changed Extruder thermistor, now lots of stringing as if printing too hot
Update: I updated the firmware and that seemed to fix the selftest issue, but I was still getting bad prints. So i disconnected the thermistor and measured resistance, and found that when moving the extruder around in the X axis the value changed. The problem was that this new thermistor doesn't have a cable straight to the board, it has a molex adapter in between. The cable was held too tight by zip ties and it was causing it to slightly disconnect with some movements. This probably made the temperature readings lower and so the extruder kept heating up.
Hope this helps anyone that runs into a similar issue! Remember to check ALL wirings.
RE: Changed Extruder thermistor, now lots of stringing as if printing too hot
Also, this is a handy link for anyone needing to replace their thermistor: https://forum.prusa3d.com/forum/original-prusa-i3-mk2-s-others-archive/thermistor-calibration/
RE: Changed Extruder thermistor, now lots of stringing as if printing too hot
If this helps anyone reading this a few years later. I just replaced mine. My experience is after you change the thermistor, your hotend isn't getting the same values as the old one. drop your hotend temp and do a 4 post string test. Keep dropping it till you get the perfect print again.
IMO proper alternative is to try and reset the values in the firmware, using either a temperature gun or thermistor on a volt meter. I haven't changed mine that way, I just wing it and try and set the hotend temp in the slicer to get good prints.
RE: Changed Extruder thermistor, now lots of stringing as if printing too hot
are you sure you got the correct thermistor?
Different manufacturers 100K thermistors have different response curves
if you install the incorrect thermistor then it will report the wrong temperature.
regards Joan
I try to make safe suggestions,You should understand the context and ensure you are happy that they are safe before attempting to apply my suggestions, what you do, is YOUR responsibility. Location Halifax UK