Bed Heater Problem - How to diagnose?

  • Hooking up new board

    Board is wired.. all except end stops at this point.. (wanted to do them once the board power and Wifi were done)

    Tied into WiFi – no problem and started to run a test or two from the Web Control screen..

    Extruder heated up no problem but ..

    When I tried the to heat the Bed it started to heat up fine (thermistor is fine - bed begins to heat up and temp rises) and then the board turned off the heater and displayed Fault ..
    It said please check wiring.. I did .. all fine..

    I am hooked up via a 40A SSR (Duet connections to DC side and 220V to AC side) .. (tested with a 3.7VDC battery and SSR works fine and heats the bed)

    Is there a way for me to see what problem is according to the board?


  • Hi,
    better information .. tried looking at the gcode generated in the web console and it generates

    12:40:52 PMError: heating fault on heater 0, temperature rising much more slowly than the expected 1.3°C/sec
    12:40:35 PMM140 S60
    12:38:39 PMConnection established!
    12:38:39 PMPage Load complete!

    Thanks for the pointer on the calibration .. trying to make heads or tails of it .. GCode is not one of my skills as yet ..


  • M303 H0 S70 <–-or whatever temp you would normally run.

    Let it do its thing. It will eventually tell you that it is done. Eventually.

    M500 after it has completed.

  • Ok, understand a bit more .. Use the GCode console and initiate an auto-tune by using the M303 command ..

    M303 H0

    .. and it appears to be heating and cooling to generate new

  • Yep, but you did put a S** afterwards, right?

  • Results:

    1:28:57 PM M500
    1:28:32 PM M307 H0
    Heater 0 model: gain 187.9, time constant 884.0, dead time 5.5, max PWM 1.00, mode: PID
    Computed PID parameters for setpoint change: P152.7, I0.173, D587.8
    Computed PID parameters for load change: P152.7, I6.839, D587.8
    1:24:55 PM Warning: Heater 0 appears to be over-powered and a fire risk! If left on at full power, its temperature is predicted to
    reach 207C.
    Auto tune heater 0 completed in 1110 sec
    Use M307 H0 to see the result, or M500 to save the result in config-override.g

    1:11:19 PM Auto tune phase 3, peak temperature was 75.8
    1:11:10 PM Auto tune phase 2, heater off
    1:06:30 PM Auto tune phase 1, heater on
    1:06:25 PM M303 H0
    Auto tuning heater 0 using target temperature 75.0C and PWM 1.00 - do not leave printer unattended

    Tuning finished and saved .. testing to 60 C now .. looks good – heated up fast and maintaining desired temp -- some type of PWM it appears .. lots of on/off cycles ..

    So a new question is. with the warning issued about it being overpowered, do I need to do something to my set-up to ameliorate the risk here??

    Thanks for the all the help here, awesome help .. this thing is way cool..

  • .. Did not put an S as it defaulted to 75 ..

  • As you use a SSR, if it fails for some reason, the bed will keep heating.
    So it is best to add a thermal fuse to the bed in your case.

  • Sounds like a good idea .. Not really happy with the PWM to the SSR .. It seems like it could cause a usage failure much faster then a bang-bang with some type of delay mechanism would .. Looking into it .. Thanks ..

  • administrators

    The bed PWM is low frequency (10Hz) so as to be compatible with SSRs. An AC mains bed heater SSR is unlikely to fail because it is massively over-rated for the task. However, for any bed heater that is capable of reaching dangerously high temperatures if left on at full power, a thermal cutout is a wise precaution.

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