E3D Titan Aero Thermal Runaway

Hi

## Background
I bought an old printer based on the Reprap Darwin, since buying it I've upgraded the controller to an Arduino Mega & RAMPS 1.4 running Marlin 1.1.9 and I've upgraded the extruder to an E3D Titan Aero (V6 & Extruder combination). This has been working great and I've done a number of successful prints lasting upto 12 or more hours.

## Problem
Recently I've started getting "Thermal Runaway" errors on the hotend. These are seemingly random but it is generally after several hours (3-6).
The first few times I noticed that the final temp measured before the shut down was roughly 195C (5 below target), following this I changed the Thermal Protection Settings to increase the Hysteresis to 10C but the failure continued only at 189C on a 200C target.
I don’t have a time frame for the temperature drop as it never happens when I’m watching and the graph on Octoprint doesn’t log long enough.

## Steps to Resolve
* Check Thermistor selection
```
5 : 100K thermistor - ATC Semitec 104GT-2/104NT-4-R025H42G (Used in ParCan & J-Head) (4.7k pullup)
```

* PID Autotune Completed & updated in Firmware.
```
// Rapman
#define DEFAULT_Kp 27.6
#define DEFAULT_Ki 2.2
#define DEFAULT_Kd 86.5
```

* Adjusted Thermal Protection Settings
```
#if ENABLED(THERMAL_PROTECTION_HOTENDS)
#define THERMAL_PROTECTION_PERIOD 80 // Seconds
#define THERMAL_PROTECTION_HYSTERESIS 10 // Degrees Celsius
```

* Checked wiring connections for Heater and Thermistor
* Measured resistance of Thermistor - 70kOhm @ 30C

The printer is currently reprinting the last file but with the parts fan disconnected to see if it avoids the problems. Beyond this I am out of ideas how to solve so am looking for any assistance / suggestions from the community.

Thanks

James

Twenty2a
Checkout the story behind the Rapman at www.twenty2a.co.uk

It sounds like the heater is disconnecting... your errors are low rather than high temperatures. If it was the thermistor disconnecting, I'd expect the temperature reading to go to 0 or some very high number. So I'd look for a loose connection or perhaps nearly-broken heater wire, perhaps inside the insulation. In particular, I'd be looking at places where the heater wires flex.

NB that this is a fire hazard (although a very unlikely one); if there is a partial disconnection, then that point can get hot, and it's not controlled via the thermistor. I've had plastic connectors melt in these circumstances.

Since it only happens after several hours, my guess is that it's triggered by your hot-end getting to some height above the bed, rather than actually time. An actual temperature-related issue would show up in minutes rather than hours.

So, whilst the hotend is cold and with the heater on (so the heater stays on continuously whilst you're probing), I'd try moving the hotend up to about where it has stopped printing in the past. Lokk for any tension on the heater wires. Then try to identify the exact location of the fault by gently (don't cause new faults!) moving/wiggling the heater wires at various places, whilst preventing them from moving everywhere else. Use a meter or perhaps put an LED plus resistor across the heater to see when it is connected or disconnected.

Thanks for the feedback I will definitely check the wiring to the heater for breaks.

I did remove and reconnect the heater to the RAMPS yesterday to check it was tight and then managed to completed a 15hrs print so maybe it was a loose connection at the RAMPS causing it. I also disconnected the parts fan for that print to see if the error occurred without the fan so will need to investigate further whether I’ve solved it or simply got lucky.

Thanks again for the input and I’ll update the thread if I find a precise cause to help others.

James

---

Twenty2a
Checkout the story behind the Rapman at www.twenty2a.co.uk