Conneting heatbed, temp readings ok but not heating up

  • Hello again 🙂

    So i outfitted my printer with a heatbed (was printing pla the whole time, so why bothering with one) and i cannot get it to work 😞

    It is this one and i can't get it to heat up. There is no info about the thermistor, so it took the info about the resistance from the webpage:
    6. Widerstand ca. 0,9 Ohm bei 12V
    7. Widerstand ca. 3,6 Ohm bei 24V ( i am running the system on 24V).

    My line in config.g looked like this:

    M308 S1 P"bedtemp" Y"thermistor" T3600 B734

    Result temp: -273.1

    Clearly the wrong thinking on my end, i then changed it to the EPCOS 100K:

    M308 S1 P"bedtemp" Y"thermistor" T100000 B4092

    Result temp: 23.3 (same as hotend readings, sometimes deviating 0.1 to 0.3 degrees)

    Great, thermistor works. Changing the status of the heatbed to active (65 degree), doesn't even start to heat, stays at 23.3° and giving this message:
    Error: Heater 0 fault: temperature rising much more slowly than the expected 1.8°/sec

    Changing again:

    M308 S1 P"bedtemp" Y"thermistor" T10000 B3988

    Result temp: -273.1

    Then [M308 S1 P"bedtemp" Y"thermistor" T100000 B3950](link url)
    Result temp: 23.3

    So it is definetly a 100K thermistor. But it is giving the same error message as above when i try to heat up the bed.
    Mosfet on the duet looks good, nothing burned etc. I wired the heatbed directly to the board, over a mosfet, changed polarity...!

    Is there anything i am doing completly wrong or is the heatbed faulty?

    Btw. the heatbed came soldered like this, maybe here is some work to do (resolder, when to measure what to measure...)?

    Thx in advance 🙂

  • @MasterOfDesaster

    you would be better posting your config.g file in full
    And which version of firmware etc

  • Ok, maybe there is something i missed (DWC is: Duet Web Control 3.1.1.).
    Everything else works fine. Still able to print.

    ; Configuration file for Duet WiFi (firmware version 3)
    ; executed by the firmware on start-up
    ; generated by RepRapFirmware Configuration Tool v3.1.1 on Sun Jun 07 2020 20:42:24 GMT+0200 (Mitteleuropäische Sommerzeit)
    ; General preferences
    G90                                                    ; send absolute coordinates...
    M83                                                    ; ...but relative extruder moves
    M550 P"Anet AM8"                                       ; set printer name
    M575 P1 B57600 S1									   ; Comms parameters for PanelDue
    ; Network
    M552 S1                                                ; enable network
    M586 P0 S1                                             ; enable HTTP
    M586 P1 S1                                             ; enable FTP
    M586 P2 S0                                             ; disable Telnet
    ; Drives
    M569 P0 S1                                             ; physical drive 0 goes forwards
    M569 P1 S1                                             ; physical drive 1 goes forwards
    M569 P2 S1                                             ; physical drive 2 goes backwards
    M569 P3 S1                                             ; physical drive 3 goes forwards
    ;M569 P4 S1                            		   		   ; physical drive 4 (E1) goes forwards
    M584 X0 Y1 Z2:2 E3                                     ; set drive mapping
    M350 X16 Y16 Z16 E16 I1                                ; configure microstepping with interpolation
    M92 X80.00 Y80.00 Z400.00 E396.83                      ; set steps per mm
    M566 X360.00 Y360.00 Z12.00 E3600.00                   ; set maximum instantaneous speed changes (mm/min)
    M203 X6000.00 Y6000.00 Z180.00 E6000.00                ; set maximum speeds (mm/min)
    M201 X1500.00 Y1500.00 Z500.00 E5000.00                ; set accelerations (mm/s^2)
    M906 X1400 Y1400 Z1400 E1400 I30                       ; set motor currents (mA) and motor idle factor in per cent
    M84 S30                                                ; Set idle timeout
    ; Axis Limits
    M208 X-50 Y-20 Z0 S1                                   ; set axis minima
    M915 X Y S30 R2 F1 			  	     				   ; set X and Y to sensitivity 30, pause when stall, filtered
    M208 X250 Y250 Z240 S0                                 ; set axis maxima
    ; Endstops
    M574 X1 S3                                             ; configure sensorless endstop for low end on X
    M574 Y1 S3                                             ; configure sensorless endstop for low end on Y
    M574 Z1 S2                                             ; configure Z-probe endstop for low end on Z
    ; Z-Probe
    M950 S0 C"exp.heater3"                                 ; create servo pin 0 for BLTouch
    M558 P9 C"" H5 A5 S0.03 F120 T6000        	   ; set Z probe type to switch and the dive height + speeds
    G31 P500 X30 Y0 Z1.65                                  ; set Z probe trigger value, offset and trigger height
    M557 X20:200 Y20:200 S40                               ; define mesh grid
    ; Heaters
    M308 S0 P"e0temp" Y"thermistor" T100000 B4725 C7.06e-8  ; configure sensor 0 as thermistor on pin e0temp
    M950 H1 C"e0heat" T0                                    ; create nozzle heater output on e0heat and map it to sensor 0
    M307 H1 B0 S1.00                                        ; disable bang-bang mode for heater  and set PWM limit
    M308 S1 P"bedtemp" Y"thermistor" T100000 B3950  ; configure sensor 1 as thermistor on pin bedtemp
    M950 H0 C"bedheat" T1                                   ; create bed heater output on bedheat and map it to sensor 1
    M307 H0 B0 S1.00                                        ; disable bang-bang mode for the bed heater and set PWM limit
    M140 H0                                                 ; map heated bed to heater 1
    M143 H0 S120                                            ; set temperature limit for heater 1 to 120C
    ; Fans
    M950 F0 C"fan0" Q500                                   ; create fan 0 on pin fan0 and set its frequency
    M106 P0 S0 H-1                                         ; set fan 0 value. Thermostatic control is turned off
    M950 F1 C"fan1" Q500                                   ; create fan 1 on pin fan1 and set its frequency
    M106 P1 S1 H T45                                       ; set fan 1 value. Thermostatic control is turned on
    ; Tools
    M563 P0 D0 H1 F0                                       ; 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
    ; Custom settings are not defined
    ; Miscellaneous
    M501                                                   ; load saved parameters from non-volatile memory
    T0                                                     ; select first tool


  • Moderator

    You're getting the error that it's heating up too slowly because RRF3 doesn't know it's a heatbed that heats slow. You need to PID tune the bed heater so it has a model of its performance.

  • I tried already to tune the bed.

    But it aborted because the heatbed was not heating up.

    The PID part in config-override.g:

    M307 H0 A340.0 C140.0 D5.5 S1.00 V0.0 B0
    M307 H1 A261.6 C97.4 D3.1 S1.00 V23.9 B0

    I am thinking, the heatbed isn't getting any signal from the board (V= 0.0).

    Is there a way to measure the voltage to find out where on the board it is broken or if only the connector is faulty? Got an multimeter at hand.

    There are no burned spots etc, everything looks fine.

  • Moderator

    Ah I see, so the bed isn't actually heating at all.

    Have you checked the voltage at the source pins on the board and at the bed itself with a multimeter?

  • So sorry for not responding earlier. Lot of work and some private things to sort out. And i ordered a multimeter for measuring 🙂

    I never needed to measure anything electrical, so i am a little noob on that end. But always willing to learn new stuff.

    So i am turning duet board on, than the wheel to 20V DC (or AC??) and then pointing the black one on the screw of the heatbed connector and the red one to point 1/2/3 at the heatbed (pic in OP)?


  • Moderator

    I'd suggest having a read of the manual for the meter. It will be able to give much better and accurate directions than I could. But in general, you want to measure the DC voltage at the bed terminals on the duet side and at the bed side.

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