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?

    Regards..





  • 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 ..

    Regards



  • 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 parameters..cool



  • 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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