Odd temperature failures

  • I've been experiencing weird hotend temp failures. The prints will be going along fine and then all of the sudden, I get negative temp spikes. Mind you, these are not complete temperature cutouts as if the thermistor disconnects, but all of the sudden, the printer thinks the hotend is much cooler, then rapidly goes back up. Here are a couple screenshots. This only happens if the printer has been running a while.

    You can see they are not gradual but spikes. The latest one is the lower one. I included the entire screen so you can see other parameters. It spiked several times and then the temp indication just dropped to 25 degrees below normal print temp, then started a slow climb before giving the error shown. You can see that the fan is not a factor as it is off.

    This is an E3Dv6 with a new thermistor. At rest, I can power the hotend up to temp then move all the wires around and get no errors or temp drops. It only happens after printing for a while. I just redid the PID tune to see if something there was causing it and that worked fine too.

    One more data point. This just started happening this past week. I had a thermistor failure that caused me to have to do the fuse bypass. Ever since then, it has been doing this. Prior to that, I've been able to print very long big prints.

  • Here is another screenshot from the second time this happened in case it helps:

  • administrators

    When you added the external fuse between VSSA and ground, which ground pin did you connect to?

  • Ground connected to the E1 Stop ground

  • administrators

    That should be ok. I think the most likely cause for the temperature reading drops is a bad connection in the thermistor wiring, although it's not impossible that whatever leakage from the heater or fan that caused the fuse to blow is responsible instead.

  • Yeah, I'm going to redo the wiring to the thermistor and see what that does. Failing that, I've got a PT100 daughterboard on the way. I have several E3D PT100 sensors laying around.


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