Huge temperature fluctuations when starting a print?

  • Hey guys,

    So I'm using a Duet Wifi with a typical e3D heater cartridge and Semitec 104GT thermistor and have been for the last four or five months without any issue. However, seemingly out of nowhere I've run into a really strange anomalous issue. When starting a print the temperature reading on my hotend will drop about 20 degrees in the space of one or two seconds, causing a heater fault warning and cancelling the print. Every now and again I've managed to pause the print upon which it will instantly shoot back up 20 degrees, but upon hitting resume the issue will occur again. There have been a couple of occasions in which, through a series of pauses and resumes, I've managed to get the printer to overcome these initial jumps in temperature and once the print gets rolling the issue seems to disappear.

    I tried replacing both the heater cartridge and thermistor with brand new replacements and that had no affect on the issue. I then tried playing around with my starting gcode, changing movement, order of actions, preheating parameters and then removing it altogether (I also played around with my pause and resume gcode) though this all had zero affect. I have also tried retuning the heater temperature control, though interestingly, 90% of the time this fails due to a bad curve fit, and on the few times it has succeeded, the issue presides and in some cases is much more extreme. I have also tried updating to the latest available firmware.

    (Whilst an issue for another day and I'm sure its unrelated but I've meaning to post about it for a while, my board also has serious issues with connection drops, I'm not sure if this is just a Duet Wifi quirk, but my connection constantly drops. Very rarely will it stay connected for more than fifteen minutes and sometimes it refuses to connect at all until I've switched the printer on and off a few times. This printer is only a couple of meters from the WiFi and I've also connected to my neighbours Wifi and taken the printer to a friends house, in which the issue remained the same)

    This is (well, was) my only operational printer at the moment and I have some customer orders to fulfill so it'd be great if anybody has some words of wisdom for me?


  • @hamiltonprops I can think of a couple of reasons. If you've changed the thermistor and cartridge, that would tend to rule out the most obvious thing which is a bad crimp or other wiring fault. Have you chnaged the print cooling arrangement recently? Because that's the next likely cause - the print cooling fan coming on and blowing cold air over the nozzle\heater block. Easy to check - just heat the nozzle then send M106 S255 to turn the fan on and M106 S0 to turn t off. If that is the cause, then you can either fit a silicone sock or change the fan ducting. Another possibility is the power supply voltage dropping. Again easy to check. When the temperature drops, loo at the input voltage or send M122 and look at the Vin min and max values. No doubt you'll get a stream of other posts with more suggestions.

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  • @deckingman I've actually just noticed after watching some video that I recorded, there is a correlation between my probe being triggered and the temperature drop, which means that somehow, somewhere, there must be some kind of crosstalk between the two. No idea what would cause this, but I'll investigate and update.

  • @hamiltonprops From re- reading your OP, you say that the temperature drops 20 degrees within a second or two. That would indicate it's not a "real" drop in temperature but rather a drop in the indicated (measured) temperature - unless your hot end has an insanely low thermal mass. So, yes I go for some sort of cross talk or electrical "noise". Are you sure you haven't got a bad crimp on the thermistor wiring somewhere?