SOLVED: bed: off current: error, hot bed temp issue



  • Hi all. I just finished installing a DuetWifi in lieu of the control box that came with my Monoprice Maker Select v2 printer, which is a Wanhao i3 Duplicator clone.

    I've worked through the other issues I ran into, and am left with (I think) one: the bed temperature is reporting that the bed is off, and that the current is "error." There's no warning or error message in the g-code console.

    I copied the config.g file from another user here who installed the DuetWifi on his Wanhao i3, changed a couple values that needed to be different from his for some reason (he had a couple motors going "forward" I had to change to "backward"), and the printer seems to be functioning otherwise. I'm doing a PLA test print on a cold bed right now, but I'd like to get this heat bed working properly so I can print some PETG, and because I prefer a 50-60C bed for PLA on glass.

    I'll include the contents of my config.g file below in case someone can have a look and see what values I set, which might need to be changed, regarding the heat bed.

    I've double-checked the mechanical connection of the heat bed power wires in the terminals, and the heat bed temp sensor wires in the socket right next to that. I could try cutting the connector off and reattaching a new connector to make sure the connections are good, but unless the temp sensor or its wiring between the control box and the printer magically went bad in between the last time I printed with the original control box and this DuetWifi, I'm betting it's some kind of configuration problem.

    The hot end nozzle is heating up fine, and its temperature seems to be reading accurately, so it's just the bed temp alone that is at issue here.

    My config.g:

    ; DuetWIFI config
    M111 S0 ; Debug off
    M550 DuetMPMakerSelectV2 ; Machine name (can be anything you like)
    M551 i3 ; Machine password (currently not used)
    M552 S1 ; Enable WiFi
    M555 P2 ; Set output to look like Marlin
    M575 P1 B57600 S1 ; Set auxiliary serial port baud rate and require checksum (for PanelDue)

    ; Movement
    G21 ; Work in millimetres

    M569 P0 S1 ; Drive 0 goes forwards
    M569 P1 S1 ; Drive 1 goes forwards
    M569 P2 S0 ; Drive 2 goes backwards
    M569 P3 S0 ; Drive 3 goes backwards

    M906 X855 Y855 Z1080 E855 ; Set motor currents (mA)
    M201 X1000 Y800 Z100 E5000 ; Accelerations (mm/s^2)
    M203 X12000 Y12000 Z120 E3000 ; Maximum speeds (mm/min)
    M566 X600 Y600 Z18 E20 ; Maximum jerk speeds mm/minute

    M574 X1 Y1 Z1 S0 ; set homing switch configuration
    M208 X200 Y200 Z180 ; set axis maxima and high homing switch positions (adjust to suit your machine)
    M208 X-8 Y-8 Z-0.5 S1 ; set axis minima and low homing switch positions (adjust to make X=0 and Y=0 the edges of the bed)

    M350 X16 Y16 Z16 E16 I1 ; set 16x microstepping with interpolation
    M92 X80 Y80 Z400 E98 ; set axis steps/mm

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

    ; Z-Probe
    ; M558 P1 X0 Y0 Z1 H3 F200 T5000 ; smart IR Z probe, used for homing Z axis only, dive height 3mm, probe speed 200mm/min, travel speed 5000mm/min
    ; G31 P500 X-45 Y45 Z0.66 ; set threshold and offsets

    ; Heaters + Thermistors
    M305 P0 T100000 B3950 R4700 H0 L0 ; Put your own H and/or L values here to set the bed thermistor ADC correction
    M305 P1 T100000 B4388 R4700 H0 L0 ; Put your own H and/or L values here to set the first nozzle thermistor ADC correction

    M307 H0 A193 C719.9 D8.7 B0 ; bed heater settings
    M307 H1 A219 C128 D13.9 B0 ; extruder heater settings

    M570 S120 ; Increase to allow extra heating time if needed

    M106 P2 T55 H1 ; Run Coldend-Fan at 55°C

    ; T0
    M563 P0 D0 H1 ; tool 0 uses extruder drive 0 and heater 1
    G10 P0 S0 R0 X0 Y0 ; set tool 0 temperatures and offsets

    ; the end
    M556 S100 X0 Y0 Z0 ; Put your axis compensation here
    T0 ; Select the first head


  • administrators

    I suggest you unplug the bed thermistor from the Duet, then use a multimeter to measure its resistance at that connector. If it's a standard 100K thermistor then at room temperature it should measure somewhat over 100k.


  • administrators

    A couple of points to help troubleshooting

    1. the bed thermistor, and thermistors in general do not have polarity.
    2. check the resistance of the bed thermistor, including the cable (at the plug, when it is not plugged into the Duet Wifi). If it is ~100K at 25C then you have a 100K thermistor which is what your cnfig is setup for (M305 P0 T100000 B3950 R4700 H0 L0) as error indicates you might have a short or other problem.
    3. If you are able to, plug in your extruder thermistor to the bed input temporarily to confirm that the bed thermistor input channel is working ok.


  • I didn't plug those numbers in to the bed temperature settings in config.g knowingly: those values were copied from this other user's Wanhao i3 config.g in the naive assumption that he has the same type of thermistor as mine. I readily acknowledge that assumption could be false.

    The cold PLA test print is still underway, so in a few minutes when it's done I'll try the tests that you guys recommend, ie: plug the extruder thermistor into the bed sensor plug to verify that the board is at least working, and then take a measurement of the bed thermistor resistance using my multimeter and make sure I've got a 100k thermistor, or possibly that there's a problem with the wiring, whichever applies.

    Btw, I am astounded at how quiet this printer is now. The multistepping or some other virtue of the quality stepper drivers in this board compared to the ones on the Melzi board has transformed this printer. If it weren't for power supply and cold end fans now I might not even know this printer was really running.



  • Ok, well the extruder thermistor worked fine in the bed thermistor spot, so I know the board itself is good.

    The bed thermistor, however, yielded an open circuit, not something around 100k. I tried the various other multimeter settings (200 ohm, 2k, 20k, 200k, 2m) to see if there was a short that would show up as very low ohms, but instead I got no reading at all.

    The wierd thing is that the wiring to the Z stop somehow magically went bad in between my last successful print with the Melzi board and when I installed the DuetWifi as well. I had to splice in a new piece of wiring to the Z stop.

    I'll flip the machine on its side and check to see if I can get a good ~100k ohm reading off the thermistor contacts directly. If I can, I'll have to splice in a new chunk of wiring.

    I thought I'd been pretty careful with the wiring bundle when I was moving it and handling it while working on this, but apparently some things came loose or something.

    I'll report back if I get the hot bed working.



  • Ok guys, be prepared to chuckle.

    When I removed the build plate to have a look at the thermistor I noticed that the color of the wiring (white teflon insulation) was different than the wiring I had going to the bed temp thermistor slot (black vinyl). Hmm.

    Coincidentally, the previous "Z Stop" switch wiring was white teflon coated, while the wiring I cut at the Z stop switch to splice in a new piece of good wire was black vinyl.

    I put a new two-pin connector on the white teflon wire, plugged it into the bed temp sensor socket, and now it all just works.

    Coincidence? I think not. 🙂

    I don't know how I managed to mislabel the wiring as I pulled it off the old Melzi board, but somehow I did.

    I have one remaining issue that I know of (at least until I try to plug in the PanelDue and 7" screen), but I'll post that in a separate thread.


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