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Active bed not heating up

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Duet Hardware and wiring
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  • undefined
    Indianagian
    last edited by 12 Dec 2018, 14:07

    ![Hello everyone, my name is Giancarlo.
    I've received my new board a Duet wifi, following the step by step guide I did set it up to work via wifi on my smartphone, I'm waiting for the lcd to come up).
    Wifi firmware 2.01
    Wifi server 1.21
    The extruder work fine, as soon as I set ACTIVE and choose a target temp it heats up, the bedheat unfortunately does not, I set a target temp on Bed at 55 °C, no heating up and no fault error
    Checked with YAT M140 and the resulting message is: Bed heater 0 (slot 0) is currently at 20.6 °C <LF>ok<LF>

    Thanks a lot

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    • undefined
      Indianagian
      last edited by Indianagian 13 Dec 2018, 08:48

      I've tried to tune the bed as per guide but....

      09:38:51 Auto tune cancelled because temperature is not increasing
      09:37:40 Auto tune phase 1, heater on
      09:37:34 M303 H0 S55
      Auto tuning heater 0 using target temperature 55.0°C and PWM 1.00 - do not leave printer unattended

      I've double checked the fuse and the 15a fuse did actually blew, the wires are connected correctly, PSU is 24v 20A 480W.
      I've set the PSU output at 23, what could have caused the short? Bed wirings are 2.5mm in diameters, how can I troubleshoot this?

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      • undefined
        dc42 administrators
        last edited by 13 Dec 2018, 13:11

        What is the resistance of the bed heater, measured with a multimeter?

        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
          Indianagian
          last edited by 13 Dec 2018, 14:31

          Hi dc42, I've checked with the multimeter, and the bed resistance is 01.8 ohm with a sensibility set at 200 on the multimeter.

          undefined 1 Reply Last reply 13 Dec 2018, 14:43 Reply Quote 0
          • undefined
            dc42 administrators @Indianagian
            last edited by 13 Dec 2018, 14:43

            @indianagian said in Active bed not heating up:

            Hi dc42, I've checked with the multimeter, and the bed resistance is 01.8 ohm with a sensibility set at 200 on the multimeter.

            If you short the multimeter probes together, you will probably get a reading of something like 0.3 ohm. Subtract that reading from the reading you got when measuring the bed heater, to get a more accurate value.

            If the resistance really is 1.8 ohms, then at 24V it will draw 13.3A, within the rating of the fuse. But if it is really 1.5 ohms then it will draw 16.7A, aboive the fuse rating.

            How large is the bed heater? Is it definitely intended for use with 24V?

            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
              Indianagian
              last edited by 13 Dec 2018, 15:00

              The multimeter probes read 0.9 ohm subtracting it to the 1.8 it's a net of 0.9 ohm.

              The bed is 300x300mm MK3A it came with a 12v psu, but on the bed itself it can be used at 24v, I've attached the bed 0_1544713138289_20181213_155715.jpg picture for visual reference.

              The reason for 24v is because I'd like to print in ABS instead of PLA only.

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              • undefined
                Dougal1957
                last edited by Dougal1957 13 Dec 2018, 15:06

                so at 24V it will draw something in the order of 26.6 Amps no wonder the fuse blew

                Can you take a good close up of the connections you have made?

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                • undefined
                  Indianagian
                  last edited by 13 Dec 2018, 15:33

                  The wires were already soldered on the bed, I didn't make any connection, as you can see the Dual power table indicate pin numbers but on the actual pin you can't find any of them, do I have to rewire the bed or should I go with a 12v psu?0_1544715199480_20181213_162924.jpg

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                  • undefined
                    dc42 administrators
                    last edited by 13 Dec 2018, 18:37

                    Are you sure that the bed heater you have really is dual voltage? If so then the best option if you have a suitable soldering iron is to rewire the heater for 24V.

                    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
                      Indianagian
                      last edited by 17 Dec 2018, 09:14

                      I've checked and the bed is dual power, would an external mosfet up to 25a be able to avoid the fuse to blow? I can lower the voltage to 21V on the psu.
                      Can this solution work?

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                      • undefined
                        dc42 administrators
                        last edited by dc42 17 Dec 2018, 13:19

                        If the bed heater is wired for 24V then it's most unlikely that it will draw more than 15A. Are there any more pads or wiring legends on the back of the board, apart from the "12V" one in your photo? What's underneath the blue tape?

                        EDIT: maybe it's really a 12V-only bed, and the 12V/24V connection instructions on the front are left over from when the original design was cloned? The instructions on the front suggest that there should be 5 pads, but in the photo I see only 4.

                        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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