Extruder Heat dropping

[CBruner]

Hi, I'm trying to print with pet, first layer 240, other layers 245. The print starts off well, temp is at 240, then 245 until about 10 minutes into the print. Then it drops to 236, then 233, then 232 and then the firmware halts.
I've tried a few different times, and closed the doors to the trident, but it always seems to happen at the same place. Any ideas what might be going on?

 

[claudermilk]

Sounds like a bad thermistor or heater. Will it PID tune? Have you just set it to a temp and let it heat soak for a while?

 

[NoGuru]

Yeah like Claudermilk said, probably a bad wire, or thermistor or heater.

 

[CBruner]

So it makes sense that the thermistor/wire/heater cuts out at the same place consistently? (I really don't want to take it apart again). Is there a way of verifying the problem without taking things apart?

 

[Le0n]

If you're lucky, the problem is in the toolhead side crimps. You can check the connectors on the thermistor and hotend without any kind of major disassembly. See if any crimps came loose and need replacing.

 

[CBruner]

Hmm, I made one last attempt. used the Prusaslicer latest alpha, and it seems to be working. At least it's past the layer that was always failing. slicer bug?

 

[Indeed]

It could also be caused by high filament flow.
It's easy to exceed what the heater can keep up with, using a standard 40W heater element and any one or more of: high print speed, thick layers, large nozzle, huge part cooling airflow.

If the flow is just above the max capacity of the heater at the selected fan speed, then after a couple of layers it would be expected to see the temperature drop despite heater pwm at 100%.
Because the slicer usually starts with a slower print speed on the first layer and then increases it for each layer, for the first maybe four or five layers.
Just like it does with the part cooling fan speed. It's to improve bed adhesion and reduce warping I think.

There is a setting in prusaslicer to limit the flow called "volumetric flow" or some such, but since I use cura I'm not yet blessed with a similar setting.
So I have to manually make sure the flow won't exceed 25 mm³/s, and that the heater block has a silicone sock, when I print PLA using a very powerful part cooling fan.
Or my weak heater won't be able to keep up.

A thicker, home-made silicone sock on the heater block may help with the heat loss due to the part cooling fan.
I'm going to try it out some day. Or maybe buy a 100W heater. Or both.