Change hysteresis value because of thermal runaway issue

We are running our Prusa i3 steel with SAV Mkl and Marlin firmware since a few months. Problems have started to appear since my son mounted a double fan to cool the print. Now we get a thermal runaway error many times. We have changed the thermistors in bed and hotend several times, and the error appears randomly at any time during the print. I believe that this could be solved by changing the hysteresis value of the function, but this seems only possible by uploading new firmware with the changed values. The problem is, I have never done that, as we received the board already with the firmware on it. Once there seems to be no way to download the firmware from the board, I am afraid to loose any setup values that then will be difficult to figure out again.

So, what can I do to find out/save the settings in my configuration.h file? Where do I change the hysteresis value - or are there other things I should check first?

Thank you for your help.

I don't know if this is the issue but some readers may be interested to know:-
Some firmware has a protection feature that checks that after first reaching your target temperature, you reach it again within a certain time. Something like 30seconds. This is to protect for the thermistor coming of the hot part and under reading.
Its possible that with the extra fans you are not maintaining your target temperature and so triggering this "fault". You should be able to monitor this on the host software by looking at the temperature plot.
If the temperature plot shows you are not maintaining the temperature, and you look to see if the heater is at 100% all the time then you will have to lower the temperature or try without the fans.
If the heater is cycling but not maintaining temperature then maybe the PID values are incorrect now you have fans. You can run a PID calibration with the fans on to get new values.
If you don't want to reflash the board with these numbers you can put them in startup Gcode in your slicer or host program. They will then be set for each file they are in.

Are you seeing thermal runaway on the heated bed, or the hot end? When I first installed 2x 50mm blower fans on mine, I would get thermal runaway of the hot end if I ran them at 100%. I found that I needed to run them at 50% and no higher. I recently insulated the hotend and this is no longer the case.

My heated bed only has thermal runaway issues if the temp is set to 110c or higher. This is mostly due to the mk2b heater struggling to reach and maintain the required temperature. If it drops more then 107.5c, I will shortly get a thermal runaway. My only solutions to this so far have been to insulate the bed both underneath, and on top where you are not printing. To do this I pause the print once 5 or 10 layers are printed and then place cardboard around the print.

My other solution is to trick the software! It will only trigger thermal runaway (Marlin firmware at least) once it has failed to reach the temperature again after a set amount of time, so if the temp drops to 108c, then I will change the desired temp to 109c, and then back to 110c. My heated bed can reach 110c again, and it usually only drops to 107c if there is a cold breeze, but it just takes too long and so tricking the software is necessary.... I have wondered if changing the hysteresis value is a better option, does this trigger the thermal runaway protection in Marlin? To be honest, I feel like upgrading my hardware would be a better, and overall safer alternative....

Quote
MCcarman
I don't know if this is the issue but some readers may be interested to know:-
Some firmware has a protection feature that checks that after first reaching your target temperature, you reach it again within a certain time. Something like 30seconds. This is to protect for the thermistor coming of the hot part and under reading.
...
If the heater is cycling but not maintaining temperature then maybe the PID values are incorrect now you have fans. You can run a PID calibration with the fans on to get new values.

Sorry, I didn't explain this very well, but exactly that is the issue. I haven't been printing via hosting software recently, only via SD card - had problems with Repetier Host. But to find out what is going wrong, I could try to print over another host (or get Repetier to work...) and see what it says.

How do I run a PID calibration?

Quote
Origamib
Are you seeing thermal runaway on the heated bed, or the hot end? When I first installed 2x 50mm blower fans on mine, I would get thermal runaway of the hot end if I ran them at 100%. I found that I needed to run them at 50% and no higher. I recently insulated the hotend and this is no longer the case. ...
To be honest, I feel like upgrading my hardware would be a better, and overall safer alternative....

So far it was always my son discovering the problem and he says the LCD message does not indicate whether the problem is the bed or the hotend. I have a print running now and he is instructed to tell me immediately if the problem appears again, then I can have a look.

I would like to avoid the upgrade for now - I am too afraid to mess up anything and don't have the time to spend days to figure things out (and bear with a cranky 12yo that can't print stuff)

How do you trick the software? Changing values while printing or do you have any program in place that changes the target temperature?

Also, have had a look at Marlin versions 1.0.2 and 1.1.0 and it seems that they have quite different hysteresis values (have them in the other computer now, but something like 40 sec and 4 deg in the newer version and 15 sec and 30 deg in the other) anyone knows whether the more actual values are considered "better" in any way?

I don't have a program for it, and anything in place like that would be circumventing the safety features of Marlin. These types of runaways usually only happen for me in the first 15 minutes of a print, so I just watch it and alter the temperature to stop. In reality though, having hardware that will maintain your temperatures well is probably much better. Have you insulated the hotend and bed at all? I have a feeling that using PID temp control rather than bang-bang temp control may also be more successful at maintaining temps, and minimizing thermal runaway. when I do my next ABS print i'll try changing my hystersis values and see if that makes thermal runaway less likely.

Okay, we finally found time to run a print, and the thermal runaway was detected within the first two minutes of the print on the hotend thermistor. Below is the temp info from the host, and it shows a very quick decrease of the temperature of about 10° within 19 seconds. After that temp starts going up again, but that is when the thermal runaway protection is triggered.

20:07:47.070 : ok T:195.1 /195.0 B:66.6 /65.0 T0:195.1 /195.0 @:115 B@:0
20:07:50.384 : ok T:194.9 /195.0 B:66.4 /65.0 T0:194.9 /195.0 @:120 B@:0
20:07:53.742 : ok T:195.0 /195.0 B:65.9 /65.0 T0:195.0 /195.0 @:118 B@:0
20:07:56.370 : ok T:194.9 /195.0 B:65.6 /65.0 T0:194.9 /195.0 @:122 B@:0
20:07:59.543 : ok T:195.0 /195.0 B:65.1 /65.0 T0:195.0 /195.0 @:120 B@:0
20:08:02.478 : ok T:195.1 /195.0 B:64.7 /65.0 T0:195.1 /195.0 @:118 B@:0
20:08:06.155 : ok T:195.0 /195.0 B:64.3 /65.0 T0:195.0 /195.0 @:119 B@:127
20:08:08.714 : ok T:195.1 /195.0 B:64.5 /65.0 T0:195.1 /195.0 @:118 B@:127
20:08:12.557 : ok T:194.7 /195.0 B:65.5 /65.0 T0:194.7 /195.0 @:1 B@:127
20:08:15.568 : ok T:192.7 /195.0 B:66.2 /65.0 T0:192.7 /195.0 @:47 B@:0
20:08:18.813 : ok T:189.5 /195.0 B:66.7 /65.0 T0:189.5 /195.0 @:112 B@:0
20:08:22.384 : ok T:186.7 /195.0 B:66.7 /65.0 T0:186.7 /195.0 @:127 B@:0
20:08:23.903 : ok T:186.2 /195.0 B:66.6 /65.0 T0:186.2 /195.0 @:127 B@:0
20:08:27.226 : ok T:185.5 /195.0 B:66.2 /65.0 T0:185.5 /195.0 @:127 B@:0
20:08:30.499 : ok T:185.6 /195.0 B:65.7 /65.0 T0:185.6 /195.0 @:125 B@:0
20:08:33.202 : ok T:186.0 /195.0 B:65.3 /65.0 T0:186.0 /195.0 @:122 B@:0
20:08:36.631 : ok T:186.3 /195.0 B:64.8 /65.0 T0:186.3 /195.0 @:127 B@:0
20:08:39.919 : ok T:186.5 /195.0 B:64.3 /65.0 T0:186.5 /195.0 @:127 B@:127
20:08:43.689 : ok T:187.1 /195.0 B:64.3 /65.0 T0:187.1 /195.0 @:127 B@:127
20:08:45.957 : ok T:187.7 /195.0 B:64.8 /65.0 T0:187.7 /195.0 @:125 B@:127
20:08:48.419 : ok T:188.0 /195.0 B:65.3 /65.0 T0:188.0 /195.0 @:126 B@:127
20:08:51.990 : ok T:188.4 /195.0 B:66.1 /65.0 T0:188.4 /195.0 @:127 B@:0
20:08:55.927 : ok T:188.8 /195.0 B:66.6 /65.0 T0:188.8 /195.0 @:127 B@:0

20:08:57.234 : Error:Thermal Runaway, system stopped! Heater_ID: 0
20:08:57.234 : Errorrinter halted. kill() called!

What could be the likely cause of this to happen?
And what could I try next to fix this problem? And yet another question: What is the meaning of the numbers behind the @?

...the smiley face doesn't appear in the host, but it sums up the situation quite well...

In Configuration_adv.h, line 66-67, bump up your numbers for THERMAL_PROTECTION_PERIOD and THERMAL_PROTECTION_HYSTERESIS :

Here's mine:

  #define THERMAL_PROTECTION_PERIOD 40        // Seconds
  #define THERMAL_PROTECTION_HYSTERESIS 4     // Degrees Celsius

So is it Configuration_adv.h and not Configuration.h that I should change? What other values in there do I need to change to adjust to my specific model? I got the printer with the firmware already configured and am reluctant to make any firmware modifications.

I would need to change the value to about 105 seconds or 10 degrees to avoid the trigger. I guess that is still safe enough to avoid the workshop burning down - but I will run more prints to find out if it behaves more or less in the same way every time. Are these values an indication of a bad thermistor? The actual temperature would certainly not decrease so quickly - but are these readings within any "normal" values for a thermistor?

I think that these settings are too aggressive by default. Both my printers screamed that the sky was falling down when I tried to print the first few times. I think that the default values that were chosen by the Marlin developers are too low, they need to be higher.

Just try bumping them up a bit, the software will shut everything down if there's a problem well before there's a risk of fire.

I don't think it's an indication of a bad thermistor, more likely an indication of a slow bed heater.

I wouldn't mess with the thermal protection numbers - better to figure out why you have the sudden drop in temp. The numbers after the @symbols look like the PMW drive values for the bed and hotend, and they seem to be maxed at 127 which is odd. What are your pid settings and max pwm values? Have you run pid tuning on the hotend?

No, I never have touched any PIDs - any good instructions for that anywhere? If I could solve it there it would be preferable.

Info on pid tuning is here: [reprap.org]

Before you do it, check the value of PID_MAX in configuration.h:

//===========================================================================
//============================= PID Settings ================================
//===========================================================================
// PID Tuning Guide here: [reprap.org]

// Comment the following line to disable PID and enable bang-bang.
#define PIDTEMP
#define BANG_MAX 255 // limits current to nozzle while in bang-bang mode; 255=full current
#define PID_MAX BANG_MAX // limits current to nozzle while PID is active (see PID_FUNCTIONAL_RANGE below); 255=full current

If PID_MAX is being set to 127 you may want to change it to 255 before running the pid tuning.

Edited 1 time(s). Last edit at 05/07/2016 12:03PM by JamesK.

I found the files for my specific model of printer: Github.com. Hopefully that enables me to change the values without rendering the printer unusable. I will have a look at the PIDs later to see if I can improve the settings.

The files in git that you linked to have the pid_max at 255, so maybe I mis-interpreted the @ numbers in your log - it was only a guess. It's worth taking the time to get familiar with the firmware for your printer, there's lots in there that you can tune and you may find you prefer a different firmware altogether. I switched from Marlin to Repetier-firmware, so I'm a bit rusty on the Marlin settings.

After changing the PID values, the problem dind't occur during yesterday's prints. Bit early to be sure about it, but I hope it remains like that!

Thank you all for your help!

...and after running some very long prints during the last few weeks, everything is still working fine! Thank you all for your help!

Hey, Im just having the same issue with thermal runaways and im gonna experiment with everything above. However could you give a summary of the main factors that did it for you? And if possible the main difference between your old and new PID settings.
Thanks!