Hot end / thermistor problem

Veti

can you measure the resistance of the thermistor with a voltmeter?
my guess is you somehow shorted the thermistor cables and the resistance is very low.

Veti

@bearcattd said in Hot end / thermistor problem:

These are what I bought:

the problem with that is that they dont tell you what the thermistor actually is.
without a supplied resistance table the temperature can easily be off by 40 degrees at 200 degrees.

BearcatTD

101.2 on the voltmeter

Veti

thats broken. it should read around 100k at room temperature.

BearcatTD

@veti Could I find a resistance table for 100k ohm thermistors and use that? Would it look like this:

http://www.bapihvac.com/wp-content/uploads/2010/11/Thermistor_100K.pdf

BearcatTD

@veti FYI I had the voltmeter selector at 200K on the resistance side.

Veti

so it was 100k.

can you swap the hotend and bed heaters around and report the temperatures?

nhof

If it indicates 9000 degrees then it's probably a short rather than thermistor values being off. NTC means resistance goes down as temps go up. A short is essentially 0 resistance so it will read an unnaturally high value. Check the leads coming out of the thermistor as those are the usual suspects.

You can generate your own beta values using a table and a calculator like so: https://www.ametherm.com/thermistor/ntc-thermistor-beta

Veti

@bearcattd

if thats the table for your thermistor then yes. if its a random one you found, prob not.

dc42

@bearcattd said in Hot end / thermistor problem:

I actually just took the thermistor out of the heater block and it immediately went down to "Normal" range...24ishC. When I put it back into the block and started to tighten the retaining screw, it shot back up to 9000c . Methinks there might be a short.

I agree, there is a short. Is it a cartridge thermistor or a bead thermistor?

BearcatTD

@dc42
It is a bead therm. I replaced the one that was bad and wired in the second one. the weird thing is, is that if I tighten down the retaining screw the temp goes crazy. so right now i have it loosely tightened (if that makes any sense) and things are working great!!

Veti

put some nylon spacer in between.

dc42

@veti said in Hot end / thermistor problem:

put some nylon spacer in between.

I doubt that Nylon will withstand the temperature of the heater block. I suggest some new glass fibre sleeving. Or change the heater block for one that accepts a cartridge thermistor.