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Slow hotend heating near target temp

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  • undefined
    pkm
    last edited by 4 Apr 2017, 12:23

    Hello,
    Since I switched to the new heating controller in 1.15, I often notice the hotend heating very slow when the temperature is 5-10C below the target.
    Sometimes it takes 2-3 minutes to go from 230C to 238C!
    I use autotuning and save the results. Did that a few times.
    What could be the problem?

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    • undefined
      Jackal
      last edited by 4 Apr 2017, 13:19

      Have you tried 1.17e or 1.18RC2?
      There has been some changes to hotend tuning.

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      • undefined
        pkm
        last edited by 4 Apr 2017, 13:23

        Yep, I just installed 1.18RC2, and before that I had 1.18beta and 1.17 something.

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        • undefined
          burtoogle
          last edited by 4 Apr 2017, 13:27

          Here's something I discovered recently… e3d v6 hotend was heating up quickly all the way to the target temp and then I had to change the hot end fan. The new fan seemed to shift a lot more air than the old one and, subsequently, the hotend struggled to reach the target temp. I swapped the fan again to one that wasn't quite so aggressive and everything's back to normal again. Maybe your hotend fan is cooling the hotend too much?

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          • undefined
            pkm
            last edited by 4 Apr 2017, 13:54

            If it matters, that's what the autotuning put to config-override.g recently
            M307 H0 A290.3 C1404.5 D1.0 S1.00 B0
            M307 H1 A722.7 C248.3 D10.0 S1.00 B0

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            • undefined
              pkm
              last edited by 4 Apr 2017, 14:00 4 Apr 2017, 13:56

              I have e3D Volcano.
              Not sure about the fan, it's been the same for a long time. And that tiny 30mm fan just can't blow too much…
              Also, the hotend heats up really fast (24V 40W heater), but only up to 5-10C below the target temp, then the curve just gets flat.

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              • undefined
                dc42 administrators
                last edited by 4 Apr 2017, 17:29

                @pkm:

                Also, the hotend heats up really fast (24V 40W heater), but only up to 5-10C below the target temp, then the curve just gets flat.

                That indicates that auto tuning has over-estimated the hot end gain. Try reducing the A parameter in the M307 H1 command by 10 or 20%.

                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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                • undefined
                  pkm
                  last edited by 4 Apr 2017, 19:33 4 Apr 2017, 19:31

                  Thanks, I'll try that!
                  IIRC autotuning said that the hotend would reach 750C at full PWM. Hard to believe, actually.
                  Also interesting that the dead time is 10s for hotend but 1s for bed… Does it make sense to decrease D to 2s?
                  I'll also try to measure average PWM at work temp.

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                  • undefined
                    dc42 administrators
                    last edited by 4 Apr 2017, 19:58

                    10s for the hot end is higher than normal, it's usually about 5s.

                    1s for the bed is extremely low. Is it a silicone heater with the thermistor embedded in the element?

                    If it's a Duet WiFi that you have, try auto tuning with firmware 1.18RC2 and see whether it gives different results. Leave out the P parameter in the M303 command (it's no longer needed), but choose the T parameter to allow for up to 10C overshoot.

                    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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                    • undefined
                      pkm
                      last edited by 4 Jun 2017, 09:24 6 Apr 2017, 08:41

                      Those were settings from 1.18RC2 autotuning…
                      I just tried once again:

                      [[language]]
                      11:39:33M307 H1
                      Heater 1 model: gain 745.5, time constant 250.1, dead time 10.0, max PWM 1.00, mode: PID
                      Computed PID parameters for setpoint change: P6.0, I0.024, D41.9
                      Computed PID parameters for load change: P6.0, I0.235, D41.9
                      11:10:55Warning: Heater 1 appears to be over-powered and a fire risk! If left on at full power, its temperature is predicted to reach 765C.
                      Auto tune heater 1 completed in 328 sec
                      Use M307 H1 to see the result, or M500 to save the result in config-override.g
                      11:07:05Auto tune phase 3, peak temperature was 211.1
                      11:06:52Auto tune phase 2, heater off
                      11:05:32Auto tune phase 1, heater on
                      11:05:26M303 H1
                      Auto tuning heater 1 using target temperature 200.0C and PWM 1.00 - do not leave printer unattended
                      
                      

                      I think this might explain something:
                      Computed PID parameters for setpoint change: P6.0, I0.024, D41.9
                      This is exactly when the problem occurs, for example changing the temp from 230C to 238C is very slow.
                      So why is I 10 times less for a setpoint change?

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                      • undefined
                        pkm
                        last edited by 6 Apr 2017, 13:43

                        The average PWM is 0.333 at 235C which corresponds to A650…

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                        • undefined
                          dc42 administrators
                          last edited by 6 Apr 2017, 14:46

                          So use A650 in your M307 command. I suggest you also try reducing D in M307 to about 5, because I don't believe that 10 is the correct value. If this causes the temperature to oscillate, then increase D towards 10 again. Reducing D will reduce the response time of the PID control.

                          The I parameter is lower for a setpoint change because using a large I parameter usually results in a large overshoot. If the gain is set correctly then the set point will still be reached quickly.

                          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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                          • undefined
                            pkm
                            last edited by 14 Apr 2017, 12:08

                            Thanks David.
                            I did a few tests and M307 H1 A650 C200 D5.0 B0 proved to work well enough.
                            Not sure why autotuning was a bit off.

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                            • undefined
                              pkm
                              last edited by 14 Apr 2017, 12:09

                              I think you can adjust autotuning to more agressive temperature rise, even if it leads to a small overshoot.

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