Wiring CoreXY. Heat Chamber wiring and Protection Circuit Questions

  • Hi,

    I am building a coreXY and i am reaching the wiring point. My set up has two hot ends, a mains bed heater, and a mains chamber heater. I also have a separate 5v power supply to power the board.

    My question is which pins should i use for the wiring to the ssr for the chamber heater and chamber heater thermistor?

    Also, my idea is to use the duet pson pins to cut power to the ac mains via 5v relay. (a 5v power supply will recieve power separately) Will it do that in response to all faults? Eg, i would expect it to kill power in the following situations:

    The hot end thermistor isn’t responding to the heating element being on.
    The heat bed thermistor isn’t responding to the heating element being on.
    The heat bed bed is going over temp (ssr stuck in on position, common failure mode of ssr)
    The heat chamber thermistor isn’t responding to its heater being on,
    The heat chamber is going over temp (ssr stuck on)

    will it kill power when any of those fault conditions exist or do i need to program it some how?

  • administrators

    Connect the SSR control input between one of the heater outputs on the expansion bus (e.g. H3) and +3.3V.

    In firmware 1.20 any heater fault will turn off the affected heater and pause the print, then after configurable timeout period (see M570 S parameter) try to turn the power off using PS_ON.



    I am having issues with the thermistor readings for heater three with the heat chamber. Looking at the pinouts, i connected on side of the thermistor to pin 35 labeled THERMISTOR 3 and the other side to VSSA pin 40 but the thermistor reads incorrect value. If i read the value of the thermistor with a multimeter i get around 120k ohm, so i think the resistor is working. In the web interface if i have the wires connected the reading gradually increases to 2000c then stops increasing, if i disconnect the wires it levels out at about 135c, again gradually.

    Must be doing something wrong but idk what.

    This is from my config.g for the thermistor setting:

    M305 P3 T100000 B4148 C2.117e-7 R4700

    And my heater setup:

    M141 H3 ; heatbed declaration
    M301 H3 P-1 ; bitbang for heatbed

    UPDATE: The issue was that I omitted the required 4.7k resistor. Added it and now i am one step closer to printing 😄

  • Hi,

    I have some wiring issues. I turned on the printer for the first time last light, and when i enabled the PSON through the the web interface the duet became unresponsive and the EXTRUDER lights would blink on and off rapidly. I immediately shut off power to the duet, and once power was reapplied (5v only) the duet was responsive again. Im not sure if i have damaged any thing, but i've done this a few times during initial troubleshooting and it seems to do the same thing each time (which makes me feel like nothing changed, and i havnt done any damage, time will tell)… but what could cause this behavior?

    I am going to take the hot end wiring apart and hook each thing up one at a time till i figure out the problem or the duet lets the smoke out, but.... is there a something i should look for specifically? One clue is that when i disconnecting the wiring harness, the heat-bed thermistor stopped working even though its not attached to the hot-end harness. If the VSSA fuse was blown, would the printer react this way if i was shorting ground and VSSA somehow (and this was bypassing the blown fuse)?

  • administrators

    What do you have connected to the PS_ON pin? Also, which Duet board revision do you have (it is printed on the top)? The 1.02 and 1.03 revisions have a self-resetting VSSA fuse.

  • Hi.

    I am not at home ATM so i cant get the Duet Board revision. But, i have a 5V relay module that pulls in two relays that close the 120v circuits to the heatbed, heat chamber, and 12v power supply.

    This is the relay module. It does not appear that the relay module is oscillating on and off, if that is what you are thinking. You can here the relay click on, but it doesn't chatter.


  • Looks like i have a duet 1.01. It doesnt seem like the VSSA fuse is blown, because i am getting a reading on the thermistors. However, the temperature is oscilating between 19c and 22c….. is that normal? It seems like AFAIK the readings were a lot more stable on my old printer using a duet....


    ON the other other hand, i was finally able to find the F1 on the duet board and i get OL over the fuse 😞

    Well, on to mouser.

    I got a lot of crap laying around, what sort of things are likely to have a 250ma fuse? (while i wait)

  • Ok,
    Just to make sure of a few things:

    I actually read 120k between the f1 fuse, my meter was out of range. I assume that still means it’s blown?

    The thing I am measuring is the thing labeled 00 in the white box marked F1

    Is that correct?

  • administrators

    Yes that means it is blown. As it is the type with metal end caps, you can solder a new one on top without removing the old one. or convert it to a resettable fuse. See https://duet3d.com/wiki/Connector_and_spare_part_numbers#VSSA_fuse.

  • Not bad for being alone in the dark!

    it now reads 3ohms, so i assume that means it’s not shorted (bypassed). With 5v power, i get correct readings from my thermistors.


    I was able to figure out the fault. I am using db25 breakout boards and a db25 cable to route wiring to my hotends/extruders and i mounted the breakout boards to an aluminum tube. Although the breakout board had insulating foam on it, when i screwed the board to the aluminum the compression allowed the pins from the screw terminals to short out against the aluminum tubing. I got the motors moving now but haven’t tried the extenders or heaters yet… hopefully my dumbassery hasn’t messed anything else on the board up.

    Thanks for building such a robust board. Short to 12v and she is still kicking 🙂

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