Duet Wifi 2 hot end heater issue



  • The hot end heater terminal block for H1 on two of my Duet wifi board burned out. (I have multiple machines)

    This happens after several hundred of hours of printing and I don't quite understand why. Everything is wired in a way that makes a short very unlikely, so let's rule that possibility out.

    The resistance on the heater is 3.7 Ohms. So in theory, a little over 3A is supplied to the single extruder heads. The board is supposed to be rated for a safe 5A.

    When I change my config file to use the H2 instead of H1, the terminal block reads close to 0V between the (+) and (-) on H2 when I turn the heater on. I get a heater fault after a few seconds, obviously.

    config.g
    **firmware version 1.21

    I am assuming a different mosfet controls each heater's 12V line through PWM. So why do I observe this behavior? and what can I do to be able to use these two boards again?

    Thanks!



  • I do not see a proper line (as far as I know) for heater 1 or heater 2 in your config.g file

    M305 P0 T100000 B4138 C0 R4700 ; Set thermistor + ADC parameters for heater 0
    M143 H0 S155 ; Set temperature limit for heater 0 to 155C
    M305 P2 X200 ; Configure sensor for heater 2
    M143 H2 S300 ; Set temperature limit for heater 2 to 300C

    The first line seems ok for the bed heater but I do not recognize the heater 2 line, the third line, as proper (but that could be just me)



  • The Duet Wifi documentation outlines how to configure the firmware for a PT100 sensor pretty clearly.

    https://duet3d.dozuki.com/Wiki/Connecting_PT100_temperature_sensors

    The third line should be correct.

    And M305 P1 X200 was used before and it worked until the terminal block of H1 failed/overheated.



  • Not my field of expertise but the usual cause of terminal blocks getting burnt out is arcing due to loose connections. Do you use ferrules? Do you check the screws for tightness periodically?



  • @Ethienne said in Duet Wifi 2 hot end heater issue:

    The Duet Wifi documentation outlines how to configure the firmware for a PT100 sensor pretty clearly.

    https://duet3d.dozuki.com/Wiki/Connecting_PT100_temperature_sensors

    The third line should be correct.

    And M305 P1 X200 was used before and it worked until the terminal block of H1 failed/overheated.

    If it is not obvious, I have never set up a PT100 sensor 😞
    What does your config-overwrite.g file look like. Are the heaters set correctly?
    Does your Duet web panel show a reasonable temperature for heater 2 (ie room temperature when the heater hasn't started yet)? If the temperature is something weird, the heater might not even be turned on because a fault is detected (ran into that with Marlin).
    BTW, if you overheated the terminal because of poor connections, there is a good chance that the solder connection on the board is defective. Have a look-see if there is maybe a barely visible crack in the solder between the terminal pin and the pcb. If so, remove old solder and resolder.


  • administrators

    @Ethienne said in Duet Wifi 2 hot end heater issue:

    The hot end heater terminal block for H1 on two of my Duet wifi board burned out. (I have multiple machines)

    This happens after several hundred of hours of printing and I don't quite understand why. Everything is wired in a way that makes a short very unlikely, so let's rule that possibility out.

    The resistance on the heater is 3.7 Ohms. So in theory, a little over 3A is supplied to the single extruder heads. The board is supposed to be rated for a safe 5A.

    The terminal blocks are rated to at least 6A. The reason for burned out terminal blocks is invariably that the screws have stopped gripping the wires tightly. This is guaranteed to happen if you make the mistake of tinning the wire ends before inserting them. Best is to use the ferrules that we supply with the Duets, if you have a suitable crimping tool. Otherwise, check regularly that the screws are still tight, especially within the first few hours and days of use.

    The terminal blocks can be replaced, if you have suitable desoldering equipment. It's possible to remove the plastic shell if you push in the barbs at the back of the terminal block. That allows you to desolder the terminals individually, which is easier than trying to desolder 2 or 4 pins at once. For 2-pin terminal blocks, I have used SMD tweezers to heat both pins simultaneously. Don't apply too much force when removing the pins, lest you damage the through-hole plating.

    When I change my config file to use the H2 instead of H1, the terminal block reads close to 0V between the (+) and (-) on H2 when I turn the heater on. I get a heater fault after a few seconds, obviously.

    You must also change the M307 H1 command to refer to heater 2.



  • @jens55 It's true it's not obvious to use X200 if you've never set a PT100 before!
    No config-overwrite.
    Yes, 21C.
    I'll have a closer look with a magnifying glass or something. There was no obvious crack or anything odd with the trace with bare eye.
    Thanks for the input!



  • @dc42 I crimped the wire ends with ferrules and did not use any solder/tin. It is possible the screw would have loosened over time though.

    Thanks for the tips for desoldering, if it comes to that I'll know what to do.

    hmm, you're 100% right I should switch H1 to H2 in the M307 command but my understanding is that if there is no M307 issued for H2, a default heater model is used. If that is the case, my original observation is still odd --> "When I change my config file to use the H2 instead of H1 [with M305 & M563], the terminal block reads close to 0V between the (+) and (-) on H2 when I turn the heater on. I get a heater fault after a few seconds, obviously."
    ...unless the firmware can't handle the fact I am issuing a M307 that refers to a heater that was not declared.

    If only the terminal block blew up because of a loose connection, why is it I can't use the other terminal block which in theory is unaffected? Might it be something else got damaged along with the terminal block?

    Thanks!


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