Spike in temperature of hotend PT100 when extruder stepper runs



  • I am just setting up a Duetwifi to run a Wanhao D6 after the D6s motherboard died.

    So hot end gets up to temperature fine, it controls OK at 180C.

    I just tried to retract the filament and the hotend temp went off the scale and the Duetwifi switched to safe. I seem to have been lucky nothing blew, except I cant find a fault so far. I was very careful when assembling the wiring…....

    Now I am stumped. I just went through all the wiring again and I can detect no short between the extruder's 4 wires and the pt100s 2 wires nor also to ground. I have tested end to end of the wanhao's ribbon cable, no joy so far.

    So I am stumped.....like huh? any ideas please?


  • administrators

    Two possibilities I can think of:

    1. Short between one of the PT100 wires and something else. But you have checked for that already.

    2. If the wiring is such that the extruder wires can induce a voltage in the PT100 wires, that could interfere with the reading. Can you post a photo of the wiring?



  • Ive like done so many checks I cant see it being a short. So near yet so far….bugger. 😞

    After the trip out the temperature graph became a little noisy just from the hold current? of the extruder's stepper? so I suspect 2 myself.

    The E0 will not run if the temp is too low (high?). is there a way to bypass that safety for testing? that way I can put a voltmeter on the pt100's leads and try and investigate a bit more.

    Off to work in a moment. I thought tonight I'd run a brand new pair for the PT100 end to end physically clear of the extruder's cabling as a test. Might be best if I go buy 2metres of shielded twisted pair for the PT100 and maybe the same in 2 pair for the extruder?

    The Wanhao uses a 16way ribbon cable, I bought a female socket and hooked into that. Sorry no idea how to upload a pic cant seem to make that work here.

    um, try this,

    http://imgur.com/a/Mi0zz

    or maybe this,

    https://postimg.org/image/b8kz9xckd/cd72cdfe/

    and,

    http://imgur.com/a/SbVOi


  • administrators

    I have the extruder and the PT100 cables following the same route for about 200mm, however they are not in a ribbon cable. I can see how running them all in a ribbon cable might increase the mutual inductance between them. So running the PT100 leads in a twisted pair may well help.



  • The ribbon cable alone is 1.5M so in fact with my wiring close to 2M. I will buy some high grade audio heavy shielded for both. I assume can just drain them to the -ve from the power supply unit on the duetwifi?

    Is there a way to bypass the limit/safety so I can leave the stepper motor to the extruder running? That way I might be able to trace what is going on if this all fails.


  • administrators

    It's nice to see someone using those extra outputs we added!


  • administrators

    @gzcwnk:

    Is there a way to bypass the limit/safety so I can leave the stepper motor to the extruder running? That way I might be able to trace what is going on if this all fails.

    M302 P1 will allow for code extrude so you can run the stepper motor while finding the PT100 issue.

    Also if you have the one to hand you can put a PT100 or similar resistor (say 180R) into the PT100 board then that will confirm that the issue is with the wiring.



  • I installed highly flexible, shielded audio cable with a drain at one end that seems to have fixed it

    😄



  • i read you can stack 2 modules, so 4 pt100s, need that to drive E3d's kraken? pretty serious stuff. I want to probably do a dual I think so this was one of the selling points of the duetwifi.


  • administrators

    Yes you can stack them in a pair on the DuetWifi for 2 PT100s or 2 PT100s and 2 thermocouples. Also another 4 channels on the Expansion board so 8 PT100s/Thermocouples in total


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