Thermistor weirdness

Hi all,

Pretty sure this is just a matter of a thermistor having gone bad, but the way in which it happened is puzzling.

See the temperature graph here:



The print was going fine until the temperature drop (195 to 190 after first layer) at which point the thermistor gave wildly varying readings for a period, then got "stuck" at around 190C even with the power turned off. I verified this by measuring the resistance across the thermistor with a room temperature hot end, showing around 720 ohms (should be about 100k ohms at room temp).

I can accept that the thermistor has somehow gone bad, but why would it just happen to get "stuck" at the temperature that the hotend is usually operating at?

Also, is there a guide for replacing the thermistor on the kit hotend? Looks like I'll need a special kind of heatshrink etc.

Thanks

- rdo

Hi,

Before replacing the thermistor I would check this is not a problem elsewhere. Disconnect the thermistor from the terminal block and measure its resistance directly. This will identify whether the problem lies at the hotend or elsewhere.

Regards,
Neil Darlow

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I try to write with consideration for all nationalities. Please let me know if something is unclear.
Printing with Mendel90 from fedora 25 using Cura, FreeCAD, MeshLab, OpenSCAD, Skeinforge and Slic3r tools.

Thermistors never fail but a common problem is burnt plastic getting onto the wires and causing a partial short. Sometimes it can be scraped off but if it has soaked into the cement the only cure is to drill it out and fit a new thermistor. We can supply spares of all the parts except the cement as we can't post liquids.

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[www.hydraraptor.blogspot.com]

Thanks Neil & Chris

I took the hotend out and discovered that the thermistor had been rubbing up against the mount, making a small hole in the insulating tape:



In this disassembled state, the thermistor reads a correct room temperature value.

What material is the red insulation tape, and/or any other suggestions for fixing the hole?

Thanks

- rdo

Actually, it looks like I probably need to take the red tape off and clean off the thermistor element. This is the temperature graph I just got when heating up the hotend (removed from the x-axis assembly, nothing touching the thermistor through the insulation hole)



- rdo

Hi,

I believe what you are looking for is a product called SILWELD manufactured by Everbuild.

Regards,
Neil Darlow

---

I try to write with consideration for all nationalities. Please let me know if something is unclear.
Printing with Mendel90 from fedora 25 using Cura, FreeCAD, MeshLab, OpenSCAD, Skeinforge and Slic3r tools.

Quote
neildarlow
Hi,

I believe what you are looking for is a product called SILWELD manufactured by Everbuild.

Regards,
Neil Darlow

Is this the same stuff?: http://www.amazon.co.uk/Super-Glue-15406-Fuse-Tape/dp/B00CAODQO6

I bought some a while ago but haven't yet got round to applying it - it'd be good to know it's the right stuff before I do!

That is what we supply. Silweld seems to be the same thing from another manufacturer.

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[www.hydraraptor.blogspot.com]