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Extruder thermistor problem

valiobgvaliobg Member, Active Member Posts: 9
I have a problem with extruder thermistor. It shows higher temperature than actual. When I heat to 100 degrees and it shows 100 in octoprint but real temperature is 80 C. Room temperature is correctly measured by the thermistor. I usually print with 205 C and when the problem occured, a cold extrusion has caused a blockage of the filament in the extruder. Now I cannot pull out the remaining filament. Is the thermistor defective ?

Comments

  • Samuel PinchesSamuel Pinches Administrator Posts: 1,536
    edited April 14
    Welcome @valiobg ,
    The max temperature on the nozzle is 250C - can you try heat to 250C and try and remove the remaining filament?

    Then, you can unplug the thermistor and measure the resistance using a multimeter. The resistance will vary with temperature:

    25C = 100k
    80C = 10.7k

    If the resistance measurement is correct, then you need to check the wiring is intact, and not damaged. Poor connection will result in lower measured temperature.



    Post edited by Samuel Pinches on
    Screen Shot 2019-04-15 at 1.15.11 am.png
    1600 x 2042 - 610K
  • valiobgvaliobg Member, Active Member Posts: 9
    I will try that. I use your firmware (Marlin 1.1.9C Beta). Da Hai gave me an advice to do the steps as in this video - https://youtu.be/brl1weuD8bs
    but isn't the problem with the lower actual temp in stock firmware fixed in your 1.1.9 version ?
  • Samuel PinchesSamuel Pinches Administrator Posts: 1,536
    It should be fixed in 1.1.8C, and I'm pretty sure I included that in the 1.1.9 beta.... so I'm not sure what is going on for you. Perhaps try 1.1.8C and see if it makes any difference?
  • valiobgvaliobg Member, Active Member Posts: 9
    I have two TMC2208 for X and Y in UART mode. They refuse two work with 1.1.8. I tried to heat to 250 real temp but filament still cannot be pulled out. It doesn't move at all. What can I do ?
  • Samuel PinchesSamuel Pinches Administrator Posts: 1,536
    Can you push and extrude? Otherwise I think you're going to have to test the thermistors and find out where the problem is...
  • Samuel PinchesSamuel Pinches Administrator Posts: 1,536
    If you touch the nozzle with scrap filament, does it melt?
  • valiobgvaliobg Member, Active Member Posts: 9
    I set to extrude with a command from the LCD and push with pliers. But it doesn't move at all. There is some melted filament which leaks from the nozzle when I heat to temp over 200 C.
  • Samuel PinchesSamuel Pinches Administrator Posts: 1,536
    Maybe there is a jam in the PTFE tubing? I think you may need to disassemble the hot end, because this does not sound like a heating problem.
  • valiobgvaliobg Member, Active Member Posts: 9
    Yes, you are right. The temp readings from the thermistor are correct. I measured the temp with another thermometer. There is a jam in the PTFE tubing probably. I have a video how to disassemble the hot end from the USB Flash stick that came with the printer. Thanks for your help.
  • Samuel PinchesSamuel Pinches Administrator Posts: 1,536
    No worries.. good luck!
  • valiobgvaliobg Member, Active Member Posts: 9
    edited April 16
    Today I found where is the problem. The filament has melted in the extruder gear. The motor reaches 52 degrees when working. It has a TMC 2208 in Spreadcycle mode programed via OTP mode. Will I have do decrease the current of the motor ? Now it is 1.32 Vref. Initially it was 1.1 V but the motor was skipping steps.
    Post edited by valiobg on
  • Enrique RiriEnrique Riri 🌟 Super Member 🌟 Posts: 36
    My solution. I updated all my 3 printers like that using TMC2208 and no more worries
    Thanked by 1Samuel Pinches
  • Der_MuckDer_Muck 🌟 Super Member 🌟 Posts: 215
    I only can say, everything over 1V is to much for those stepper motors. Not one motor of my JG is over 0,8V and with that, they will stay warm.  Before my extruder motor was untouchable after 20min printing.
    I also add cooling ducts on the extruder but it was for nuts because with 0,750 the extruder motor will get little warm. 
    Maybe its a problem of the TMC2208 that it skips steps and so you need higher V but thats not optimal at all.
    P.S. 1,32 is much to high
    You can also check your Y motor, mostly that motor is constantly to hot wile printing.
  • Samuel PinchesSamuel Pinches Administrator Posts: 1,536
    To reduce the extruder motor force required, you can shorten the bowden tube length (it is excessively long) and you can add some canola oil to tube to help lubricate the filament.
  • Der_MuckDer_Muck 🌟 Super Member 🌟 Posts: 215
    Or higher the print temperature, to low temps. equal in a higher extruder motor force to. I had that problem with TPU but it equals more in filament slipping.
  • ufodoctor3ufodoctor3 🌟 Super Member 🌟 Posts: 35
    Replacement of the temperature sensor at the extruder
    Hello Forum
    If you need to exchange the NTC temperature sensor of the extruder, I found out
    by measurements at the JGaurora5 electronics/display and consulting the data sheets,
    that the Digi-Key Sensor 495-2125-ND (B57540G0104F000 from EPCOS) is compatible with
    the original JGaurora sensor for about 5$ only!
    Good luck
    Peter

    Thanked by 1Samuel Pinches
  • valiobgvaliobg Member, Active Member Posts: 9
    I successfully fixed the problem. Now temp of motor is 31 C. Was 52 C.
    Thanked by 1Samuel Pinches
    2019-04-21 07.49.14.jpg
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