Thermistor help

Discussion in 'Analog & Mixed-Signal Design' started by TheQuestor, Aug 2, 2018.

  1. TheQuestor

    Thread Starter New Member

    Aug 2, 2018
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    I have a 3d printer and it came with what I was told a 100k Ohm thermistor. I bought a bag full of what was described as 100k ohm thermistors but when I hook it up to my printer's motherboard the temp is WAY off. It should read about 29C but it reads like 86C which leads me to believe they are 10k Ohm thermistors, not 100k Ohm,

    Can I just put a resistor inline to bump it up to 100k and if so what size resistor
    .
    Thanks in advance.
     
  2. paulktreg

    AAC Fanatic!

    Jun 2, 2008
    722
    159
    Your series resistor will not change with temperature and you'll just throw everything out.

    What 3D printer do you have? What does this thermistor do? Why did you buy a bag? Does it fail regularly?

    The more information the better.
     
  3. AnalogKid

    AAC Fanatic!

    Aug 1, 2013
    7,032
    1,991
    You can insert a resistor in series. but the result will be correct for only one temperature. For example, if you put 90K in series with a 10K thermistor, it will read 100K at +25C. But the combined resistance will not be correct for any other reading.

    Note that thermistors usually are not interchangeable among manufacturers. Two different parts will read the same at the calibration temperature, but the response curve with respect to temperature will be slightly different, because each manufacturer has its own formula for the temperature sensitive material.

    ak
     
  4. TheQuestor

    Thread Starter New Member

    Aug 2, 2018
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  5. Reloadron

    Distinguished Member

    Jan 15, 2015
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    No, you can't just place a fixed resistor in series with what you have. If the system was designed to work with a 100 K NTC thermistor then you need a 100 K thermistor and you also need one with the same dimensions as the broken one so it fits in the thermo-well the same as the old one.

    Here is what I suggest you do. Rather then screw around with Ebay or similar looking to buy a bag in bulk I suggest you look at a data sheet from a reputable manufacturer or distributor like this one or like this one. I also suggest you note what AnalogKid points out where he covers:
    They will be close and this is why I suggest reading the data sheets and taking note of the dimensions as well as the uncertainties. While I can buy a bag of ten on Ebay or Amazon for about $0.50 each I would rather buy from a company like Mouser or Allied and pay Twenty USD for a bag of ten and know what I am getting.

    If you have an ohmmeter measure the resistance of one that you have at average room temperature, the difference between a 10K and 100K should be obvious at room temperature close to 25 degrees C. Warm it up and note which way the resistance goes, up or down?

    Ron
     
  6. dendad

    Well-Known Member

    Feb 20, 2016
    1,957
    509
    If you know the thermistor type, the 3D printer firmware can be re-flashed to suit it.
    In the Marlin firmware, Configuration.h file, there is something like this...


    // @section temperature

    //===========================================================================
    //============================= Thermal Settings ============================
    //===========================================================================
    //
    //--NORMAL IS 4.7kohm PULLUP!-- 1kohm pullup can be used on hotend sensor, using correct resistor and table
    //
    //// Temperature sensor settings:
    // -3 is thermocouple with MAX31855 (only for sensor 0)
    // -2 is thermocouple with MAX6675 (only for sensor 0)
    // -1 is thermocouple with AD595
    // 0 is not used
    // 1 is 100k thermistor - best choice for EPCOS 100k (4.7k pullup)
    // 2 is 200k thermistor - ATC Semitec 204GT-2 (4.7k pullup)
    // 3 is Mendel-parts thermistor (4.7k pullup)
    // 4 is 10k thermistor !! do not use it for a hotend. It gives bad resolution at high temp. !!
    // 5 is 100K thermistor - ATC Semitec 104GT-2 (Used in ParCan & J-Head) (4.7k pullup)
    // 6 is 100k EPCOS - Not as accurate as table 1 (created using a fluke thermocouple) (4.7k pullup)
    // 7 is 100k Honeywell thermistor 135-104LAG-J01 (4.7k pullup)
    // 71 is 100k Honeywell thermistor 135-104LAF-J01 (4.7k pullup)
    // 8 is 100k 0603 SMD Vishay NTCS0603E3104FXT (4.7k pullup)
    // 9 is 100k GE Sensing AL03006-58.2K-97-G1 (4.7k pullup)
    // 10 is 100k RS thermistor 198-961 (4.7k pullup)
    // 11 is 100k beta 3950 1% thermistor (4.7k pullup)
    // 12 is 100k 0603 SMD Vishay NTCS0603E3104FXT (4.7k pullup) (calibrated for Makibox hot bed)
    // 13 is 100k Hisens 3950 1% up to 300°C for hotend "Simple ONE " & "Hotend "All In ONE"
    // 20 is the PT100 circuit found in the Ultimainboard V2.x
    // 60 is 100k Maker's Tool Works Kapton Bed Thermistor beta=3950
    // 70 is the 100K thermistor found in the bq Hephestos 2
    //
    // 1k ohm pullup tables - This is not normal, you would have to have changed out your 4.7k for 1k
    // (but gives greater accuracy and more stable PID)
    // 51 is 100k thermistor - EPCOS (1k pullup)
    // 52 is 200k thermistor - ATC Semitec 204GT-2 (1k pullup)
    // 55 is 100k thermistor - ATC Semitec 104GT-2 (Used in ParCan & J-Head) (1k pullup)
    //
    // 1047 is Pt1000 with 4k7 pullup
    // 1010 is Pt1000 with 1k pullup (non standard)
    // 147 is Pt100 with 4k7 pullup
    // 110 is Pt100 with 1k pullup (non standard)
    // 998 and 999 are Dummy Tables. They will ALWAYS read 25°C or the temperature defined below.
    // Use it for Testing or Development purposes. NEVER for production machine.
    //#define DUMMY_THERMISTOR_998_VALUE 25
    //#define DUMMY_THERMISTOR_999_VALUE 100
    // :{ '0': "Not used", '4': "10k !! do not use for a hotend. Bad resolution at high temp. !!", '1': "100k / 4.7k - EPCOS", '51': "100k / 1k - EPCOS", '6': "100k / 4.7k EPCOS - Not as accurate as Table 1", '5': "100K / 4.7k - ATC Semitec 104GT-2 (Used in ParCan & J-Head)", '7': "100k / 4.7k Honeywell 135-104LAG-J01", '71': "100k / 4.7k Honeywell 135-104LAF-J01", '8': "100k / 4.7k 0603 SMD Vishay NTCS0603E3104FXT", '9': "100k / 4.7k GE Sensing AL03006-58.2K-97-G1", '10': "100k / 4.7k RS 198-961", '11': "100k / 4.7k beta 3950 1%", '12': "100k / 4.7k 0603 SMD Vishay NTCS0603E3104FXT (calibrated for Makibox hot bed)", '13': "100k Hisens 3950 1% up to 300°C for hotend 'Simple ONE ' & hotend 'All In ONE'", '60': "100k Maker's Tool Works Kapton Bed Thermistor beta=3950", '55': "100k / 1k - ATC Semitec 104GT-2 (Used in ParCan & J-Head)", '2': "200k / 4.7k - ATC Semitec 204GT-2", '52': "200k / 1k - ATC Semitec 204GT-2", '-3': "Thermocouple + MAX31855 (only for sensor 0)", '-2': "Thermocouple + MAX6675 (only for sensor 0)", '-1': "Thermocouple + AD595", '3': "Mendel-parts / 4.7k", '1047': "Pt1000 / 4.7k", '1010': "Pt1000 / 1k (non standard)", '20': "PT100 (Ultimainboard V2.x)", '147': "Pt100 / 4.7k", '110': "Pt100 / 1k (non-standard)", '998': "Dummy 1", '999': "Dummy 2" }
    #define TEMP_SENSOR_0 5
    #define TEMP_SENSOR_1 5
    #define TEMP_SENSOR_2 0
    #define TEMP_SENSOR_3 0
    #define TEMP_SENSOR_BED 0
     
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  7. Reloadron

    Distinguished Member

    Jan 15, 2015
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    That was really good and thanks for sharing that.

    Ron
     
  8. TheQuestor

    Thread Starter New Member

    Aug 2, 2018
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    0
    wow great reply. Unfortunately finding out what brand/manufacturer/data sheet from Zonestar is pretty much impossible. Sigh.
    It's a custom board running Repetier and has worked very well for me for the last 2+ years I have used this Prusa i3 clone but like I said I like to keep a bunch of stuff on hand :)

    I tend to refuse to buy from places like Mouser or Allied as they totally gouge on shipping. Why pay 30 cents for a part then 15 bucks in shipping [yah I am being a TAD snarky here but still] When I can get 10 for that with free shipping :). I do buy from them on certain things but VERY rarely.
    I'd love to be able to get the data specs from Zonestar and then buy a dozen or so from whomever just to have on hand.

    I'd rather not have to mess with custom firmware really as I really like using Repetier Server/Host as it has served me quite well for the 2+ years and hundreds of prints I have done with this old clone.

    I've already replaced almost every [printed] part on this thing with parts of my own design [using tinkercad...stop laughing] but so far the only thing I have run into issues with are now these thermistors. Looks like they go back in the drawers [i bought them last year] and will just deal with the 1 extra I had from a couple hotend heat blocks I bought from ebay. Yah those do work as intended lol. But I get what you're saying,
     
  9. dendad

    Well-Known Member

    Feb 20, 2016
    1,957
    509
    I don't knock TinkerCAD as it is the one I use too. For some reason. I have not been able to get my old head around any other program.
    Yes, I know about postage! Recently, I purchased some stuff from Sparkfun and, as I live in Australia, the post was a bit over $70.
    The whole order was on the expansive side, and I wavered about buying it but decided to go ahead. Then after clicking "ok", I remembered the exchange rate. So it was about half again more than I was thinking, in $AU.

    As for your printer temp, if it is stable, just work out what to set it to for a good print and use that. On my Deltaprintr, I have a problem that the fan is cooling the thermistor, and instead of fixing it, I just edit the gcode file to make sure the fan is on first, then print at "175C", and that is around 195C really. It works fine.

    The gcode was..
    M109 S175.000000 ; set temperature to 175C
    M106 S255 ; start with fan on 100%

    now..
    M106 S255 ; start with fan on 100%
    M109 S175.000000 ; set temperature to 175C

    I really should fix it but my Deltaprintr is working really well so I will leave it alone.
     
  10. TheQuestor

    Thread Starter New Member

    Aug 2, 2018
    4
    0
    Same here with tinkercad. I actually really like it lol. Anyway I

    I did a little testing and the large green thermistors are almost there, about 5C off of delta but that's closer than the small black ones which are about 40+C off delta but I'm just going to use one of the small clear ones I pulled off another block as it reads pretty much dead on,

    I had a fan prob until I designed my own lol also on my old single blocks I had an issue when the fan kicked on [usually on or about the 8th layer] it would cool down 10+C so I wrapped it with that thermal cotton and boom, no more issues. It's kind of a pain to work with but does wonders
    https://www.ebay.com/itm/5pcs-lot-3...-3mm-Heat-Insulation-Cotton-Thick/30272971165
     
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