Custom thermistor

General Discussion
1

Regarding the custom thermistor. I am setting Klipper and for extruder options, I am using a custom thermistor because none of the common ones work (generic semitec or max ). I don’t have a specific name of my thermistor but I got it from an old printer. Using Marlin with thermistor 147 which is pt100 pull up 4.7k worked fine. Setting the following settings shows 275 C , ADC out of range
[thermistor my_thermistor]
temperature1: 25
resistance1: 103180
temperature2: 150
resistance2: 1366.2
temperature3: 250
resistance3: 168.6

2
  1. A PT100 cannot be connected directly, it needs an amplifier like the MAX3186.
  2. A thermistor that does not work with Generic 3950 is likely not a NTC
  3. Without any information on the type, it will be very hard to support
  4. Please follow How-To Ask for Help for all future requests
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3

You don’t have a custom Thermistor. Looking at your numbers, I can see that it’s an NTC and it’s a 100k NTC Thermistor with a Beta of 4369.

Using measured values like you have, you can calculate your Beta value using a tool like:

As @Sineos said, when asking a question, please provide all the requested information when you put in your post.

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4

This configuration worked for pt100:
sensor_type: PT1000
pullup_resistor : 47000

5

I’m quite sure that this does not work or at least does not give any reliable results. Again, a real PT100 PTC cannot be attached to a regular thermistor port (A PT1000 PTC can be attached this way).
For PT100 an amplifier board is mandatory.

6

ll take your word. It’s unreliable because the room temperature is 20 more or less and the thermistor marks 25C. so error is high but for testing its ok . Ill change in future to a reliable one . What is the thermistor that works pretty fine with Klipper and is also reliable?

7

What you are doing for testing is completely on your side, but please be so kind to refrain from stating that something is working, which apparently is not. Other users here are reading it as well and will be lead to believing this.

4 Likes
8

Can you describe how you made your measurements at temperature (ie how do you know that the thermistor is at 250C - or even 25C) as well as the equipment that you used?

9

Ive used a fluke multimeter for temperature and resistance

10

I think, @mykepredko also wanted to know how you measured.

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11

I don’t get it completely. I compared the value from the octoprint which was 25 C and the physical measurement which was 20-21 C, that was all

12

In other words: Where did you put the heat sensor of the multimeter to the hotend?

13

Sigh.

I guess you don’t understand a) the need to provide complete and accurate information to the people who are offering to help you and b) that if you want to use a thermistor for accurate readings, you need accurate data.

In your original post, you put in specific values for specific temperatures:

[thermistor my_thermistor]
temperature1: 25
resistance1: 103180
temperature2: 150
resistance2: 1366.2
temperature3: 250
resistance3: 168.6

Going back to your original post:

The reason why Klipper went tilt is because you put in values that aren’t based on reality and the actual resistance of the thermistor at temperature is different than what you set it for and the algorithm used to determine the actual temperature based on the resistance measured came up with an invalid temperature.

I have no idea what you have - you may have an NTC or a PTC thermistor and there’s no way of knowing which based on what you’ve provide.

14

That was wrong configuration of my_thermistor . I don’t know how to set a custom thermistor in klipper , I’ve tried to take some values from Marlin but didn’t work . This was my last answer and working one I have now for testing with ± 5 C :

This configuration worked for pt100:
sensor_type: PT1000
pullup_resistor : 47000

15

We’re willing to work with you on this but wouldn’t it be easier just to buy a thermistor of known parameters?

16

Sure . I am on it . Thanks