Heater fluctuation

  • I am using a E3D V6 with silicone sock and Semitec thermistor.The set up is 12v and it is giving me some problems after I mistakenly erased my entire sd card on the Duet Wifi.I have everything working just fine now but the heater is randomly having issues.I have repolaced the heater and thermistor and have checked all the wiring and I am certain that isn't the issue.The problem I am having is that the heater graph stays flat for hours and then it just kind of gets very weird fluctuations in temperature.The graph will then go perfectly flat again sometimes for hours or just a few minutes and the fluctuations start again out of nowhere.I have tried with the autotune and without.The autotune will always give me heater fault after heater fault when used.This is how my heaters are set up in my config.g folder.

    ; Heaters
    M307 H0 B0 S1.00 ; Disable bang-bang mode for the bed heater and set PWM limit
    M305 P0 T100000 B3950 C0 R4700 ; Set thermistor + ADC parameters for heater 0
    M143 H0 S110 ; Set temperature limit for heater 0 to 120C
    M305 P1 T100000 B4725 C7.06e-8 R4700 ; Set thermistor + ADC parameters for heater 1
    M143 H1 S290 ; Set temperature limit for heater 1 to 290C

    0_1551728497621_Screenshot 2019-03-04 14.12.57.png

    0_1551728564763_Screenshot 2019-03-04 14.42.13.png

    This final picture is after the auto tune and all three are with the fans off.I am printing PETG without using the fans so I know that isn't the problem.
    0_1551731822446_Screenshot 2019-03-04 15.35.11.png

  • If it's one of the cartridge thermistors I just had one start going wacky on me and it was the wires having issues close to the heater block. I noticed it when I touched/moved the thermistor wires a little bit and the hotend fan would turn on and off.

    I would start looking there for them possibly shorting.

  • administrators

    Sudden negative temperature excursions when using a thermistor indicate either a short from the thermistor to a higher voltage (e.g. heater or fan), or a bad connection in one of the thermistor wires. If you have the old style bead thermistor (not the cartridge type) then shorts between the thermistor wires and the hot end metalwork are very common.

  • I will check the wiring and I am using a E3D cartridge style thermistor.I checked the wiring and even tried moving the wires closer to the cartridge body while the machine was printing but I could not reproduce the problem.

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