Thermal Runaway issues on Ender 3 Pro even after replacing thermistor and heater cartridge

Question

I have an Ender 3 Pro with the BTT SKR E3 V2.0 mini with Marlin firmware 2.0.8.2.x. I am trying to print PETG, which requires decently high temperatures.

I initially replaced the stock board after a thermal runaway event that seemed to have damaged it. After installing the new board and getting all the settings dialed in (typically 260 °C hotend and 90 °C bed), it worked great for about 2 weeks until I got the thermal runaway event error again.

Here is what I have tried so far

• replaced the thermistor with this
• replaced the heating cartridge with this
• replaced the hotend with this an all-metal one
• measured voltage coming from the power supply and coming out of the board going to heater cartridge (both ~24 V)

I PID tuned the printer using M303 E0 S260 C10 and stored new PID values in EEPROM + firmware. A note, running this multiple times seemed to constantly increase the P and D values. I stuck with the initial values given (kP 13.97 kI 0.84 kD 57.96). I still continued to get thermal runaway events.

I then tested the heater cartridge and thermistor with my multimeter. The heater was 13.5 ohms which seems about right. I was unable to measure the thermistor value. Searching online shows I likely need a better multimeter to do so. It's possible it is bad, but I find that hard to believe considering this issue was happening prior to my replacing it.

Example log of the failure happening. All I did was heat the printer up, leave it on for a bit, set it to cool down briefly, then tell it to heat up again. The printer was heated for ~5-8 minutes before this log starts.

Could this be the board again, or is there something else I'm missing?

Answer 1

I'm fairly certain I have solved this issue, and it ended up having nothing to do with the printer and everything to do with what it was plugged into!

I had it on a smart outlet with some automations set up to kill the power if there was ever a fire. Unfortunately, the outlet I was using was only rated for 8A, while the Ender 3 Pro can draw up to 15 amps. When it was unable to draw more than 8A to heat the hotend, this likely caused the printer to think there was a problem, triggering the thermal runaway failsafe.

After moving it to an outlet with a higher amperage rating, I have had no more issues.

Answer 2

Recv: T:224.24 /260.00 B:88.95 /90.00 @:127 B@:127

You are trying to achieve too much!

The maximum rated temperature for an Ender3 is 260 °C, yes, but to achieve this you need to insulate the heater block with a silicon sock from losing heat to the surroundings and with some tinfoil from an airstream over it from the cooling fan. And even then, you are trying to work at the absolute maximum the printer can theoretically reach - which means it is above the temperature you can operate it while printing.

Likewise, you try to have the bed at 90 °C and that is too high to consistently reach with the heater installed.

To print at those elevated temperatures you need different gear:

• You absolutely need a heated chamber.
• You need a specialized hotend that does not suffer heatcreep and is rated to at least 275 °C
• The rest of the printer needs to be able to work at those elevated temperatures.

Answer 3

I run a small print farm made up of Ender 3's with SKR Mini 2.0 boards. We print ASA, ABS, and Nylon with Nozzle temps of 245-260 °C and bed temps of 105 °C. This is all done without a heated enclosure. There is no reason for your Ender 3 to not be able to do this as well.

My first check would be the attachment of the thermistor to the heat block. Any chance this got dislodged and isn't taking accurate measurements? Does it have a good thermal connection to the heat block? I haven't seen this type of thermistor before. How does it connect to the hotend?