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Mass Portal Pharaoh ED, RADDS 1.5 , Thermistor problems

blysprutanblysprutan
in Motherboard
Hi!
I just got a Pharaoh ED.
When i got it the printer was partially disassembed due to some problems (Not shure what?)
I have now assemled it completely but now i am stuck.
The thermistor for the hotend was broken when i got it, so i replaced it with a 100K thermistor.
Not shure if that is the right one but something is wrong.
The temp for the bed is correct. but the hotend reads 72C and when i heat it up i get all kinds of numbers.
I have tested two different thermistors with same result.
Also it is not connected to the place where thermistors is supposed to be connected according to the manual.
They are connected to AUX/ADC and 5V (See picture) https://ibb.co/nRy4vRv
I have worked with this for 12 hours straight now and i am out of ideas.
Pse help.

Comments

  • RepetierRepetier
    That place is not for thermistors. It is for thermo-couple if firmware is configured for it. You need to connect a shield then there that converts e.g. PT100 signals to correct voltage as there is no thermocouple chip build in.

    If it used a thermistor the normal connector for first extruder is T0 in the Thermistors header. Just hope it was configured for it. 
  • blysprutanblysprutan
    Repetier said:
    That place is not for thermistors. It is for thermo-couple if firmware is configured for it. You need to connect a shield then there that converts e.g. PT100 signals to correct voltage as there is no thermocouple chip build in.

    If it used a thermistor the normal connector for first extruder is T0 in the Thermistors header. Just hope it was configured for it. 
    Thanks mate!
    I have a Thermo-Couple from a multimeter and when connecting it i get the right values :-)
    So far so good. 
    I hope i can get it up and running soon.
    The printer have some kind of chip for it since the Thermo-couple goes to before it enters the board.
    Do you have any advice on how to insulate the probe before putting it into the hotend?
    I read that putting it in there without insulation it will be shorted and not read anything correct.
  • RepetierRepetier
    Ok getting shorts would in deed be a problem. We average several measurements so it can jump in temperature if it switches between short and correct resistance. Kapton tape is a good and thin insulator if you have. Electric tape should also work. Do you have also the correct Thermo-couple type? PT100 is most common but there are different types that would also behave different.
  • RAyWBRAyWB
    edited July 2022
    Just for clearance , PT100 is a PTC thermistor(100 Ohms) which increases resistance by rising temperature ,
    most common in 3dPrinters  are the NTC thermistors (100KOhms) which decrease resistance by rising temperature.

    Thermocouple is a voltage-output sensor based on combination of alloys for example a (source:Wikipedia)

    "Type K (chromel–alumel) is the most common general-purpose thermocouple with a sensitivity of approximately 41 µV/°C.[11] It is inexpensive, and a wide variety of probes are available in its −200 °C to +1350 °C (−330 °F to +2460 °F) range. Type K was specified at a time when metallurgy was less advanced than it is today, and consequently characteristics may vary considerably between samples. One of the constituent metals, nickel, is magnetic; a characteristic of thermocouples made with magnetic material is that they undergo a deviation in output when the material reaches its Curie point, which occurs for type K thermocouples at around 185 °C "

    i guess you have a Type-K thermocouple wich is very common and the most reliable way to isolate it is a galvanic islolation of the Thermocouple amplifier to printer electronic what means , separate power supply and galvanic isolation of data lines (guess its a spi-connection) with optocouplers or special digital isolatiors.

    edit: should be an analog signal in your case and the Chip should be AD595 (necessary thermocouple type K).

    Isolating with kapton tape may work , but not reliable as its temperature range ends at about 260°C whats close to hotend temperature.
    I guess there are thermocouples on the market which are isolated by aluminiumoxide or cement but i don´t know where to buy.
    I prefer the galvanic isolation as it´s a "clean" but high effort solution.

    to keep it simple my suggestion is to try to get original replacement or depending on your skills use standard 100K NTC , reconfigure and compile Firmware for use of the T0 input





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