Wrong Thermistor readings

General Discussion
1

Hello,

If I need to start a new thread, please tell me.

  1. My heater for an EPCOS 100K does not seem to get understood by the software.
  2. It was working. Now, not so much.
  3. It starts reading at 175C when it is most likely at around 23C.

So, when I heat the heater w/ PID Calibrate, PID Calibrate gets interrupted.

Seth

P.S. Is this wiring or a config issue? I just fixed my poor wiring and then the same error keeps occurring.

Update

I have no way to tell what exact thermistor I am using. I grabbed it from the older model (discontinued) Monoprice Maker Select Plus.

Should I use a different thermistor or try another code for the thermistor?

Another Update

The heater on the heater_block heats exceptionally well and quickly but the thermistor reads at 125C to 175C w/out interacting w/ reality. If anyone has had this issue, please send guidance.

2

On an unknown NTC type use Generic 3950 as type.

The differences between the types are a few degrees at best. If you get higher deviation, you either have a wiring issue or a dead thermistor.

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3

Hello @Sineos ,

I am sorry. The heater seemed to be heating awful fast. I think I figured out the issue.

  1. Wanhao had MOSFETS on the HOTEND heater(s) and other parts…
  2. There was some other circuitry for the hotend they presumed handles 24v and pinmux.

Dang it. I am goin’ to have to make some modifications. Do you have any ideas? My reading from the hotend is starting at EPCOS 100K but does not matter b/c of the 24v input and NO MOSFET(s).

Seth

P.S. Heater GND has/had four, separate MOSFETs attached. So, I need to figure out what I can do to this board to handle such a circuit.

4

Not sure that I understand what you are reporting.
Generally speaking:

  • The board’s connectors for hotend and bed have MOSFETs otherwise it will not work at all
  • Thermistor readings and MOSFETs and / or speed of the heat up process are unrelated
  • The board will toggle the MOSFETs via PWM to reach the target temperature. The way how it toggles them is controlled by a PID loop, which matches thermistor reading versus target value
  1. Make sure your thermistor is delivering the right value at room temperature
  2. Perform a PID tuning for the bed or hotend
5

@Sineos ,

Okay…

  1. The thermistor is not reporting the right value of the heater_block at room temp.
  2. The PID tuning gets interrupted for the hotend at 170C.

I will attempt some rework ideas and hang something off the end of this Recore to handle the stepdown conversion. I think I have just what it will take.

Seth

P.S. I may be back, though (I know this is not a complete hardware related discourse). So, I will not attempt to see it fit for me to get into electronics as much as I should. Who knows? Maybe I may!

6

As long as you have not tackeld this issue, it is futile to look at anything else.

Just to avoid hunting a red herring:

  • On a typical printer-board, the ports for thermistors / bed / hotend should work “out of the box” with the provided settings for the respective board
  • If you get wrong readings but closely followed the instructions for your board, then most likely the thermistor is dead
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7

Good notion. I will attempt a thermistor replacement and then move from that point forward.

Seth

8

Quick input: A simple test could be hanging the bed’s thermistor to the hotend port. If now your temperature is roughly room temperature, then the thermistor or thermistor wiring is to blame.

9

Cough and yeppers,

Dang wiring. I checked it again and again. I rewired everything to make sure and again, it worked and then was interrupted. I think I could learn some from some wiring pros.

Seth

10

Okay,

I cannot say for one that it was me. The thermistor is damaged from abuse. Anyway, I replaced the thermistor and bam, things are back to working!

Seth

P.S. Thank you, @Sineos , for putting up w/ my random ramblings of no ideas to help. So, thank you. I will post less hopefully. Right?

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