Heated chamber heater fault

  • I am setting up a heated chamber for a rather large 3D printer that is almost fully enclosed. There is small opening at the top of the front plate of the printer. The heating element is 750W and placed at the bottom of the printer. A small fan pushed out the hot air from the heating element. Another 12V, 0.7A fan, placed near the top of the printer, forces convection in the build volume. The thermistor is placed about 600mm away from the heating element outlet, near the top of the printer, on the opposite side; far from both the fans air flows outputs.


    Every time I try to set the heated chamber temperature to 55C, I get a heater fault, a few seconds in, signalling that the temp rise is much below the expected 1.8C/s. There is no way the thermistor would record such a fast heat up. It takes several minutes for the temperature to hit 55C and that is fine for my design needs. I set the M307 command to the lowest possible gain with A10. I don't understand what goes on behind the scene with the heater model using Bang-bang so I am clueless as to how to get this setup to work without a fault flag getting raised.

    Note that I get a fault when I try to use M303 to find the model parameters.

    Any advice would be welcome!

  • @Ethienne My setup differs slightly from yours, but you can pick the lines you need from my code (in config.g) and adapt them to your situation.

    ; Setting up the chamber heater:
    M141 H3 S-273.15 R0				; heater #3, initially 0 degrees, off
    M305 P3 X4 R4700 T100000 B3950			; Chamber Top sensor controls heater
    M307 H3 A11 C900 D30 B1				; define heater model parameters manually
    ; Adjust chamber heater fault detection:
    M570 H3 P300 T25				; allowed deviation before heater fault: < 300 secs, ± 25 degrees 
    ; Setting up temperature sensors of the chamber:
    M305 P103 X3 S"Chamber PTCs" R4700 T50000 B3950	; direct thermistor for heater #3 (we use two thermistors)
    M305 P104 X5 S"Chamber Bottom" R4700 T100000 B3950; Bottom sensor, just for info
    ; Connecting fans to the chamber heater:
    M106 P3 L0.2 X0.7 T40:180 H103;
    M106 P4 L0.2 X0.7 T40:180 H103;
    ; Protect chamber heaters against overheating:
    M143 P100 H3 X103 A2 C0 S150			; shut-down heaters temporarily if exceeding 150 degrees

    Please note that you must adjust the parameters of M307 and M570 according to your situation; for safety reasons, you should try to narrow them down just to avoid heater faults. Don't allow for anything - you risk to burn your house.

    The main difference to your setup is that I have paired each PTC with a thermistor, so that I can limit the max. temperature of the heaters.
    As I use two PTCs (and two groups of fans as well), the thermistors directly attached to the PTCs run in parallel, thus having a nominal resistance of 50k instead of 100k (T parameter in M305 P103…).

  • administrators

    To allow M303 H3 to run successfully, try increasing the D parameter in the M307 command for your chamber heater to 60. If you are using a config-override.g file, make sure that it doesn't include a M307 command that will override that.

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