Printer Model: Anycubic Mega X
MCU / Printerboard: BTT Skr 3
Describe your issue:
Hi!
I have a problem, when I try to heat up my bed it is working fine. It stays on the target, but when I start the extruder, my bed is increasing his temperature but the led on the bed itself is not on, so its not heating. After a few minutes the bed temperature stays high but when i touch the bed it is colder then before. So the thermistor is reading wrong values, but I dont understand why that problem only appears when im heating up the extruder.
Yes here. klippy.log (596.7 KB)
Here I heat up the Bed to 75, then i wait until it stays ans heat up the extruder. The temperature from the bed is heating up without a higher target.
Maybe during heating the extruder, the hotend is too close to the bed thermistor under the bed. Try a different or higher position of the extruder during heating.
What makes me wonder: Why does the runaway protection does not kick in?
No the hotend could not be too close i tried this already. The werid things is after a few minutes it goes down to the target and after 10 minutes of printing it goes from 75 to 100 and more in a second an then the runaway protection kicks in. And the next things is that my idle temperature is 34 degrees Celsius, on both heaters, buth that cant be true becuase in my room it has only 22, when I unplug the heater beds thermistor on the MCU, the extruder drops to 22. So I think i will try to buy a new thermistor for the bed, or do you have any other suggestions?
I think because of line 1324 in the attached klippy.log above.
Yes, first thing to try.
But (if a new NTC termistor behaves the same), I did a very quick spreadsheet extraction of your klippy.log. Sorry, I forgot the timestamps (I use excel at work, openoffice always gives me a hard time). analysis.zip (11.5 KB)
The readings of your bed NTC thermistor are looking good.
Have you implemented new macros before your problem occurred? You use a lot of macros. If yes. I would remove the latest macros.
max_temp gives the level of the maximum temperature the device should be able to reach. It has nothing to do with the runaway protection. But: 200°C for a bed is quite high anyway.
But the strange thing is that the temperature from the bed is increasing wirhout a higher target, and when i touch the bed during print its going to be colder and the power led on the bed is not on, so its not heating but increasing temperature. Also my idle temperature is too high, it says 39 but in my room its only 21.
Then it might be a issue with the board. If there is current (heating up), but the control pin is low (bed off), then something is wrong with the hardware.
Does the bed also heat when you just the heat the hotend alone?
Yes, when I heat up the Hotend in Klipper the Heater beds tempererature is increasing, but the led on the bed is not on so it is not heating. The next weird thing is that i unplugged the thermistor cables on the board (hotend, heater bed) an the idle temp on both is 23, so it dropped from 39 wich is fine, but the problem is still there.
For me this looks like some (serious) hardware issue. Potentially some “stuck” MOSFETs that do no longer cut off current to the bed, potentially only an issue with the thermistors.
I would consider a printer in this state inherently unsafe to use.
After unplugging the two thermistor everything is working fine again. I dont know what the problem was but i definitly will replace the thermistor for the heater bed. Thank you for your help!
My question was meant, how is runaway protection implemented in the Klipper code?
I’m a safety nazi, better save than sorry! Means, avoid fire risk in the first place and electrical risk second (that’ll probably hurt just me)!
Living in an apartment house, I try very hard to make sure not to start a fire!
Hurting anyone with my hobby would also be fatal for me. I guess, I couldn’t continue to live.
Before starting FDM printing, I build this, use it and check it every 3 month.
