Thermistor problem

Discussion in 'E3D-v6 and Lite6' started by alclonky, Jul 6, 2014.

  1. alclonky

    alclonky Member

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    if i heat the thermistor to the 285 mentioned in the manual, the thermistor has an short peek, just enough to trigger the max temp prodection of the firmware
     

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  2. Ralph Hilton

    Ralph Hilton Well-Known Member

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    You can alter the triggering temperature in configuration.h
    Se the lines: (Marlin)
    // When temperature exceeds max temp, your heater will be switched off.
    // This feature exists to protect your hotend from overheating accidentally, but *NOT* from thermistor short/failure!
    // You should use MINTEMP for thermistor short/failure protection.
    #define HEATER_0_MAXTEMP 300
    #define HEATER_1_MAXTEMP 275
    #define HEATER_2_MAXTEMP 275
     
  3. alclonky

    alclonky Member

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    the problem is not the maxtemp setting, its the peek to 700° for a second which has to be a missreading of the thermistor?
     
  4. Ralph Hilton

    Ralph Hilton Well-Known Member

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    I would think that it must be a short circuit either in the wiring or from a faulty thermistor.
     
  5. musaprendel

    musaprendel New Member

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    suspect thermistor.

    Received my hotend yesterday, have thermistor set as Semitec (azteeg x5 smoothie, default config) in config, autotune to 285, but temp output appears to go to +385 for very short periods. When I see above 285 kill it but it is too late.

    When autotune to 180-220 the temps spike up. Applying the autotune kP kI kD settings seems to make no difference to the fluctuations.

    Even just hitting the set temp at 220, the temps rocket past set temp to ~315, all over the place. Fluctuates +-30'c around set temp. Have checked the voltage/amperage draw to board and the hotend fan, all good, it is a 30amp 12v regulated lab power supply.

    See same symtoms on my gen6 board running marlin.
     
  6. tailgunner30uk

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    You probably need to check, but I believe there is a setting in the Config.H file for Marlin/Repetier, and something similar in other firmwares, that allows for an average of a number of readings to be used from the thermistor.
    This cuts down the effect of random fluctuations in the readings causing failed prints due to temperature misreadings.
     

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