Is this a failing Thermistor, or something else? (Hotend Temp wait hotter than Set)  

RE: Is this a failing Thermistor, or something else? (Hotend Temp wait hotter than Set)

Remember that the heating element is on the back of the heater block and the thermistor is on the front of the heater block, and the heater block is aluminum.  You will see thermal differentials across the block as heat is transferred up the heat break and down the nozzle (think of these as essentially fins on a heat sink).

I can't say if 25c differential is normal, but it doesn't sound abnormal. 50c seems a bit high.  You might try the E3D-V6 Copper Heater Block with nickel plating for better heat conduction over the aluminum block.

ps: there are two thermistors in the part number group E3D specs. they are not the same values at temp.  You might verify you have the correct thermistor. Both measure 100k at 25c, but diverge as temperature ramps up.  It would explain the differences you are seeing if indeed you have the wrong thermistor.

RE: Is this a failing Thermistor, or something else? (Hotend Temp wait hotter than Set)

RE: Is this a failing Thermistor, or something else? (Hotend Temp wait hotter than Set)

Don't forget thermal sensors rely on the emissivity of the item in question and shiny objects will mess with the reading. I suspect this may be part of the issue.

RE: Is this a failing Thermistor, or something else? (Hotend Temp wait hotter than Set)

I would have just replaced the thermistor. It's much cheaper then the IR camera :). Can you describe what kind of strange issues have you got with ASA/CPE?

RE: Is this a failing Thermistor, or something else? (Hotend Temp wait hotter than Set)

Posted by: Tim

Remember that the heating element is on the back of the heater block and the thermistor is on the front of the heater block, and the heater block is aluminum.  You will see thermal differentials across the block as heat is transferred up the heat break and down the nozzle (think of these as essentially fins on a heat sink).

I can't say if 25c differential is normal, but it doesn't sound abnormal. 50c seems a bit high.  You might try the E3D-V6 Copper Heater Block with nickel plating for better heat conduction over the aluminum block.

 

ps: there are two thermistors in the part number group E3D specs. they are not the same values at temp.  You might verify you have the correct thermistor. Both measure 100k at 25c, but diverge as temperature ramps up.  It would explain the differences you are seeing if indeed you have the wrong thermistor.

I also expected a different reading between the "internal" sensor and the outside of the heater block. That's why I cross checked with the second MK3 I have at work. To see how much differnce I can expect from the Sensor readings and the Thermal camera. To my surprise those readings (interal vs. camera) were very close. (the working printer was set to 250. Thermal cam said 254°C max.)

Oh and my printer is a kit. I printed 1,1km Filament so far and it worked fine until recently.. So I think the thermistor was OK before. But good to know that there are different Versions. O_o

RE: Is this a failing Thermistor, or something else? (Hotend Temp wait hotter than Set)

Posted by: nikolai.r

I would have just replaced the thermistor. It's much cheaper then the IR camera :). Can you describe what kind of strange issues have you got with ASA/CPE?

pssssssst! Don't say this so loud. I am kind of a nerd and don't go for the most sane option sometimes. It just happens...

I printed with Filamentum CPE. I used it before and really like it. My Profile (that worked outstanding before) was at around 270 / 275°C. When I print it now it is super stringy, it stinks...

At first I suspected bad / wet Filament, but both (brand new spools) behaved the same, even after drying.

I tried to print a heat Tower to tune it back in.  I started with 280°C.... (specs are 255 - 275 °C). At the time the printer settled at 280°C, the Filament was just "liquid", it was so hot that the opaque filament, was actually transparent when it came out of the nozzle. Oh yes... and the smoke. Have a look at the smoke! 😎

I really have very little doubt that the printer is way too hot. The only thing I don't know is: is this a thermistor Issue? It it possible that it kind of works up to 200°C and then falls apart?

RE: Is this a failing Thermistor, or something else? (Hotend Temp wait hotter than Set)

Oh yes. Looks really like the hotend is way too hot. Replace this cheap thing (thermistor) and try again.

RE: Is this a failing Thermistor, or something else? (Hotend Temp wait hotter than Set)

What smoke?

Thermistors fail in odd ways, generally they crack (there are glass envelop parts inside a metal case). When they crack they begin falling apart, raising their resistance (show colder than expected temps).  So a failure is consistent with what you are seeing.  A new thermistor is cheap, and what Prusa asks for one with proper length and termination is worth the extra cost (especially in Europe where they will mail a part);  I probably wouldn't try to DIY unless I knew for certain what the full part number E3D uses it. 50-50 chance you'll get the wrong one.  Maybe someone knows the proper R value for the thing at 100c and will post up. 

RE: Is this a failing Thermistor, or something else? (Hotend Temp wait hotter than Set)

Ok, jurst ordered a new one. Together with the MK3 -> MK3S upgrade kit. Thanks for your help everyone.