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    Hot end auto-tuning failed due

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    • Dougal1957undefined
      Dougal1957
      last edited by

      If it is a clone V6 then it is likely to have a thermistor with a B Value of 3950 specified at 25/50 degrees and not the same as the E3D ones maybe thats the issue?

      resamundefined 1 Reply Last reply Reply Quote 0
      • resamundefined
        resam @Dougal1957
        last edited by

        @dougal1957 I performed a successful auto-tuning about 8-9 months ago, and I didn't change my thermistor settings since then...
        Next thing on my list to check is wiring and the thermistor itself - and maybe replace it.

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        • Dougal1957undefined
          Dougal1957
          last edited by

          fair do's

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          • dc42undefined
            dc42 administrators @resam
            last edited by dc42

            @resam said in Hot end auto-tuning failed due:

            Well, now I'm printing at 257C - and the fluctuations get quite big now... up and down of almost 10C in total.

            If the fluctuations are regular oscillations (not caused by e.g. the print cooling fan turning on), increase the dead time (D parameter in M307) until they stop. The kink you are getting in the tuning temperature curve is causing the dead time to be under-estimated.

            Dead time should be independent of temperature, so try the 3.2 seconds that you were using before.

            Duet WiFi hardware designer and firmware engineer
            Please do not ask me for Duet support via PM or email, use the forum
            http://www.escher3d.com, https://miscsolutions.wordpress.com

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            • resamundefined
              resam
              last edited by

              I now tried various combinations of parameters and configs - no luck.
              The kink goes down too quickly to be caused by actual cooling - so I'm guessing this must be some other non-heat-related measurement error...0_1529099981641_Screen Shot 2018-06-15 at 23.58.00.png

              PSU voltage stays fairly constant at 24.1 - 24.2V.
              30mm hotend cooling fan comes on at full power at 50C and does not blow on the heater block. No part cooling fans are active.

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              • dc42undefined
                dc42 administrators
                last edited by

                I agree, the kink looks like a firmware artefact. It's on my list to see if I can reproduce it.

                Duet WiFi hardware designer and firmware engineer
                Please do not ask me for Duet support via PM or email, use the forum
                http://www.escher3d.com, https://miscsolutions.wordpress.com

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                • resamundefined
                  resam
                  last edited by

                  I didn't find any wiring issues or other obvious faults, but I did manage to play with the model parameters to get a stable temperature while printing. I do get a big initial overshoot of 10-15C when heating up from a cold state, but after that has settled down, I get a stable 257C with +/- 0.5C.

                  My old model was M307 H1 A539.5 C221.2 D3.2 S0.80 V24.1 B0
                  (auto-tuned a few months ago).

                  My new model is M307 H1 A560.0 C130.0 D10.0 S1.0 B0
                  (tweaked by hand until I saw a flat temp curve).

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                  • dc42undefined
                    dc42 administrators
                    last edited by

                    The initial overshoot suggests that you have set the gain too high or the time constant too low. I find it suspicious that your new time constant is half the value you had from auto turning. Also your dead time is very high and will prevent the PID from reacting very fast.

                    Duet WiFi hardware designer and firmware engineer
                    Please do not ask me for Duet support via PM or email, use the forum
                    http://www.escher3d.com, https://miscsolutions.wordpress.com

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                    • resamundefined
                      resam
                      last edited by

                      @resam said in Hot end auto-tuning failed due:

                      M307 H1 A560.0 C130.0 D10.0 S1.0 B0

                      I didn't fine tune it yet - I just tried with D5.0 and it was even better, less initial overswing, and also stable at 255C.
                      I did notice another oddity, when I used DWC to set the heater to 0C (i.e., OFF), I got another weird kink (far right)!
                      0_1529309932158_Screen Shot 2018-06-18 at 10.16.50.png

                      Is my 24V 40W heater somehow affecting the thermistor reading when I turn it off? Voltage drop on the ADC reference?

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                      • dc42undefined
                        dc42 administrators
                        last edited by

                        Yes I think there is an interaction between your hot end heater being powered and the temperature sensor. But it's unlikely to be the ADC reference. What type of temperature sensor are you using?

                        Duet WiFi hardware designer and firmware engineer
                        Please do not ask me for Duet support via PM or email, use the forum
                        http://www.escher3d.com, https://miscsolutions.wordpress.com

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                        • resamundefined
                          resam
                          last edited by

                          cheap E3D v6 clone with 24V 40W heater and old-style thermistor glass bead.
                          M305 P1 S"Hotend" R4700 T100000 B4725 C0.0000000706

                          The original wires of the thermistor are about 10cm long, and then plug into a 2-pin dupont connector on a small PCB. From there it goes over a CAT5e+RJ45 cable to the Duet, about 70cm away. I think read somewhere that connectors/plugs might influence the thermistor measurement, but I don't remember for which type this was a concern...?

                          dc42undefined 1 Reply Last reply Reply Quote 0
                          • dc42undefined
                            dc42 administrators @resam
                            last edited by

                            @resam, please check that the thermistor connections are well-insulated from the hot end metalwork. Shorts between the leads of that type of thermistor and the heater block are common.

                            Duet WiFi hardware designer and firmware engineer
                            Please do not ask me for Duet support via PM or email, use the forum
                            http://www.escher3d.com, https://miscsolutions.wordpress.com

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