Bed heater fault above 60C

  • I am having an odd issue getting my bed heater to reach temp. It seems to work up to about 58-60C (temperature on the Web Interface matches my IR sensor) but then it shoots to 2000C and faults. Once it cools a bit, it returns to the 58C and continues to track the cooling properly. If I clear the fault and try to heat again, it creeps up to around the 60C range and then faults again. It is a standard 100K thermister and it was working with the original controller board.

    [c]; Configuration file for Duet WiFi (firmware version 1.20 or newer)
    ; executed by the firmware on start-up
    ; generated by RepRapFirmware Configuration Tool on Sun Feb 25 2018 13:46:09 GMT-0700 (US Mountain Standard Time)

    ; General preferences
    G90 ; Send absolute coordinates…
    M83 ; ...but relative extruder moves

    ; Network
    M550 PFDM1 ; Set machine name
    M551 Preprap ; Set password
    M552 S1 ; Enable network
    ;*** Access point is configured manually via M587
    M586 P0 S1 R8090 ; Enable HTTP
    M586 P1 S0 ; Disable FTP
    M586 P2 S0 ; Disable Telnet

    ; Drives
    M569 P0 S1 ; Drive 0 goes forwards
    M569 P1 S1 ; Drive 1 goes forwards
    M569 P2 S1 ; Drive 2 goes forwards
    M569 P3 S1 ; Drive 3 goes forwards
    M350 X16 Y16 Z16 E16 I1 ; Configure microstepping with interpolation
    M92 X80 Y160 Z2268 E115 ; Set steps per mm
    M566 X1200 Y1200 Z60 E300 ; Set maximum instantaneous speed changes (mm/min)
    M203 X30000 Y30000 Z300 E2700 ; Set maximum speeds (mm/min)
    M201 X9000 Y9000 Z100 E1000 ; Set accelerations (mm/s^2)
    M906 X800 Y800 Z800 E800 I30 ; Set motor currents (mA) and motor idle factor in per cent
    M84 S30 ; Set idle timeout

    ; Axis Limits
    M208 X0 Y0 Z0 S1 ; Set axis minima
    M208 X200 Y200 Z200 S0 ; Set axis maxima

    ; Endstops
    M574 X2 Y2 Z2 S1 ; Set active high endstops

    ; Z-Probe
    M558 P0 ; none present

    ; Heaters
    M301 H0 S1.00 P10 I0.1 D200 T0.4 W180 B30 ; Use PID on bed heater (may require further tuning)
    M305 P0 T100000 B4138 C0 R4700 ; Set thermistor + ADC parameters for heater 0
    M143 H0 S120 ; Set temperature limit for heater 0 to 120C
    M305 P1 T100000 B4138 C0 R4700 ; Set thermistor + ADC parameters for heater 1
    M143 H1 S280 ; Set temperature limit for heater 1 to 280C
    M570 H0 S2000 ; Slow bed heater to increase fault time

    ; Fans
    M106 P0 S0 I0 F500 H-1 ; Set fan 0 value, PWM signal inversion and frequency. Thermostatic control is turned off
    M106 P1 S1 I0 F500 H1 T45 ; Set fan 1 value, PWM signal inversion and frequency. Thermostatic control is turned on
    M106 P2 S1 I0 F500 H1 T45 ; Set fan 2 value, PWM signal inversion and frequency. Thermostatic control is turned on

    ; Tools
    M563 P0 D0 H1 ; Define tool 0
    G10 P0 X0 Y0 Z0 ; Set tool 0 axis offsets
    G10 P0 R0 S0 ; Set initial tool 0 active and standby temperatures to 0C

  • administrators

    I think something is expanding and that expansion is causing a short either between the two bed thermistor wires or between one of the wires and something else conductive.

    If it always occurs at the same temperature, then the expansion and short circuit are probably in the vicinity of the bed heater. If instead it occurs after a certain amount of time, to the actual temperature at which it occurs depends on the starting temperature of the bed, then it could be happening in the Duet.

  • Yup. It was a bad connection. At the connector, though. When I shoved probes into the top of the 2 pin connector to monitor what was happening, I couldn't get it to fault. So, although I know this isn't the recommended procedure, I went ahead and flowed some solder into the crimp connections and it seems to be working fine now. Odd that it came and went with temperature - definitely not what I would have expected for a bad connection at the board but there it is.

  • administrators

    I'm glad you solved it. The bed thermistor connection is close to the bed heater MOSFET, so the connection will have been heating up with the MOSFET.


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