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Erratic bet temps followed by heater fault

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  • undefined
    Co3get
    last edited by 17 Jun 2020, 02:51

    Help me think this through. I'm having a hard time heating my bed up. it goes up smoothly to about 65 or so, then gets erratic with small variations, small 'jumps'. it struggles along and eventually faults.

    I've checked my connections a few times. My SSR is a new panasonic. Ideas?

    Photo is trying to heat up to 90 degrees:

    Screenshot (6).png

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    • undefined
      Phaedrux Moderator
      last edited by 17 Jun 2020, 04:30

      What is the heater and thermistor? How are they configured?
      What is the error message you get?
      What firmware version? What board are you using?
      Have you PID tuned the bed?
      Post your config.g.

      Z-Bot CoreXY Build | Thingiverse Profile

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      • undefined
        jens55
        last edited by 17 Jun 2020, 05:42

        I had exactly the same issues - it turns out this is a faulty sensor in the heat bed. I ended up installing a separate (external to the heat pad) sensor and all issues went away. I use the old defective sensor as a secondary sensor that is displayed on my graph but is not used for control purposes.

        undefined 2 Replies Last reply 17 Jun 2020, 13:47 Reply Quote 1
        • undefined
          deckingman
          last edited by 17 Jun 2020, 05:47

          I agree with @jens55 . That temperature trace is noise. The real temperature cannot have such rapid excursions. It's either a faulty sensor or a wiring problem such as a bad crimp.

          Ian
          https://somei3deas.wordpress.com/
          https://www.youtube.com/@deckingman

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          • undefined
            Co3get @jens55
            last edited by 17 Jun 2020, 13:47

            @jens55 I have been thinking along these lines, I have a big red heat pad with a built in sensor. Were this any other printer I'd replace the bed thermistor and be done. What sensor did you use?

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            • undefined
              jens55
              last edited by 17 Jun 2020, 14:54

              Just a standard thermistor like you get on hot ends. Taped to the underside on top of the heater with Kapton tape

              undefined 1 Reply Last reply 17 Jun 2020, 15:09 Reply Quote 1
              • undefined
                jens55
                last edited by 17 Jun 2020, 14:56

                Don't forget to re-run tuning for the bed when the new sensor is hooked up.

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                • undefined
                  Co3get @jens55
                  last edited by 17 Jun 2020, 15:09

                  @jens55 said in Erratic bet temps followed by heater fault:

                  Just a standard thermistor like you get on hot ends. Taped to the underside on top of the heater with Kapton tape

                  That's pretty smart. middle of the bed?

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                  • undefined
                    Co3get @jens55
                    last edited by Co3get 17 Jun 2020, 15:20

                    @jens55 Can you explain you you set up the old sensor as a graphed secondary sensor?

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                    • undefined
                      jens55
                      last edited by 17 Jun 2020, 17:53

                      @Co3get, here is my heater section of config.g:

                      ; Heaters

                      M308 S0 P"bedtemp" Y"thermistor" T100000 B4200 ; configure sensor 0 as thermistor on pin bedtemp
                      M308 S3 P"e2temp" Y"thermistor" A"bed sense 2" T100000 B4200 ; configure alternate or second bed heat sensor
                      M950 H0 C"bedheat" T0 ; create bed heater output on bedheat and map it to sensor 0
                      M140 H0 ; set bed heater to heater zero
                      M143 H0 S120 ; set temperature limit for heater 0 to 120C
                      M307 H0 B0 S1.00 ; disable bang-bang mode for the nozzle heater and set PWM limit
                      M308 S1 P"e0temp" Y"thermistor" T100000 B4200 ; configure sensor 1 as thermistor on pin e0temp
                      M950 H1 C"e0heat" T1 ; create nozzle heater output on e0heat and map it to sensor 1
                      M143 H1 S280 ; set temperature limit for heater 1 to 280C
                      M307 H1 B0 S0.6 ; disable bang-bang mode for the nozzle heater and set PWM limit
                      M308 S2 P"e1temp" Y"thermistor" T100000 B4200 ; configure sensor 2 as thermistor on pin e0temp
                      M950 H2 C"e1heat" T2 ; create nozzle heater output on e0heat and map it to sensor 2
                      M143 H2 S280 ; set temperature limit for heater 2 to 280C
                      M307 H2 B0 S0.6 ; disable bang-bang mode for the nozzle heater and set PWM limit

                      It's been a while since I set that up so am not too sure what all was done.
                      I do know that in order to display the second bed temperature on the graph in DWC, you need to go into the 'Extra' bit of the 'tools and extra' pane and flip the 'show in graph' thingy.

                      Hope that helps.

                      Yes, middle of bed for the sensor, offset a bit to not be directly where the bed wires go into the heat pad. I don't think it makes much difference exactly where it is located as long as it is somewhere in the middle-ish.

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