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Nozzle temp too low, PT100 sensor ok, what could the problem be?


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Posted · Nozzle temp too low, PT100 sensor ok, what could the problem be?



My UM2+ does not reach correct Nozzle temp.

If I set it to 240°C it reaches 215°C. I checked the PT100 sensor and it measures ok, 190 ohms at 240°c. I also measured a reasonably correct resistance on the main board when the UM2 is turned off, so it does not seem to be a problem with the main board connector. If the sensor is disconnected with the UM2 is on it reports an error, as it should.


I have also calibrated the temp measure instrument used to double check the nozzle temp.


So, any ideas what is causing this problem?



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    Posted (edited) · Nozzle temp too low, PT100 sensor ok, what could the problem be?

    please check:

    • heater cartridge cold resistance ok?
      • while un-powered, can be tested with ohm meter directly at mainboard heater terminals while heater is connected. mind polarity, though: negative lead of meter must go to +24 V terminal on J21, positive lead must go to heater terminal on J21. setting = OHMS (or DIODE). if swapped, reading may be wrong.
      • don't have value at hand, maybe somebody else can chime in and report. i would expect it to be R = V^2 / P =  576 V^2 / 25 W = 28 Ohms (but no more than 30 Ohms). if more, cartridge is bad, if ok, check:
    • power supply voltage good at heater terminals while powered and heating up?
      • if not, check power supply and MOSFET Q3.
    • when set to 100 °C , does the nozzle read 100°C after heat-up, or is it lower?
      •  if it reads 100°C,  check fastening of heater cartridge in olsson block. maybe heat transfer from cartridge to olsson block is impaired.







    Edited by Porkpie
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    Posted · Nozzle temp too low, PT100 sensor ok, what could the problem be?

    Clearly it's not the sensor.  Good debugging.  So obviously the heater can't get it hot enough.


    Is this happening while printing?  Or even during heat up.  For example I can't even print at 210C with a 0.8mm nozzle with 0.4mm layers printing at 60mm/sec.  The original heater just can't keep up.  Even if I turn the fans off.


    So it could be you need a more powerful heater (3dsolex sells 35,40, and 50 watt heaters for um2).


    Or it could be your fans are blowing on the nozzle.


    Or very common, your metal fan shroud is touching the heater block.  That's common if you took it apart recently.  Make sure you can slip a piece of paper from the rear between the block and the shroud.  Or just try removing the fan shroud temporarily to see if it can now heat up to 240 just fine.  The fix is usually to rotate the round nut which will raise up the heater block a little more.


    Or maybe there is resistance somewhere in the cabling to the heater or something that Porkpie mentions above.

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