MK2S preheat Bed Thermal Runaway error - while temperature is increasing
I have a MK2S connected to octoprint. This allows me to monitor the exact temp, on a graph. Whenever I try and preheat my printer to ABS temps (255/100), while the bed temperature is increasing, the firmware throws a thermal runaway error and shuts down the print. The issue is, the bed temperature is regularly climbing and not crashing (which I assume is the point of the thermal runaway). If I sit there and repeatedly restart the connection and preheating, it can eventually reach up to ~90 degrees, after around an hour (lol). Steps taken so far include:
- Screwing the Pot in PSU to give the bed 12.5V (measured with multimeter)
- Checked Resistance (~1.5 ohms)
- Unplugged and replugged bed thermistor and heater in RAMBO
- Checked Fuses
- Turned off fan cooling (even though it happens during preheat, not during a print)
Additionally, the Bed's LED stays on, and there are no melted cables.
RE: MK2S preheat Bed Thermal Runaway error - while temperature is increasing
It sounds like the heat bed is taking too long to heat up,
What is the voltage across the heatbed terminals, whilst the heatbed is heating?
the Mk2 is a 12 VOLT so any stray resistance will have a significant effect, often the cable starts to deteriorate and go high resistance as strands break in the conductors
the original cable is 16AWG. if the terminal voltage is low, you could replace the wires with 14AWG flexible silicone wire, which has a lower resistance
regards Joan
I try to make safe suggestions,You should understand the context and ensure you are happy that they are safe before attempting to apply my suggestions, what you do, is YOUR responsibility. Location Halifax UK
RE:
The voltage across it is 12.5 Volts. I screwed the POT in a bit more to ensure it was over 12, as it was 11.5 before. I'm measuring the Terminals in the Rambo, not the soldered pads on the heated. Should I be checking that as well?
14AWG is a good idea, thank you. Should I be concerned about strand count or anything else besides AWG? Ill likely buy from Ali if it is not an issue.
RE: MK2S preheat Bed Thermal Runaway error - while temperature is increasing
Hi Leo,
you should be measuring at the solder pads. on the heatbed.
strandcount is important, the Prusa wire probably has about 22 strands,
Flexible silicone wire has a lot more finer strands, which makes it less likely to break, in use
at this site on ebay
eBay item number:176373249402
the 14AWG wire has 400 strands
regards Joan
I try to make safe suggestions,You should understand the context and ensure you are happy that they are safe before attempting to apply my suggestions, what you do, is YOUR responsibility. Location Halifax UK
RE: MK2S preheat Bed Thermal Runaway error - while temperature is increasing
So the 18awg wire finally arrived and I immediately soldered it.... only to run into the same issue. 12.7V measured across my beds solder joints
RE: MK2S preheat Bed Thermal Runaway error - while temperature is increasing
18AWG has a lower current capacity than 16AWG or 14 AWG,
using 18AWG wire will cause a greater loss in the wiring and lower power delivery to the Heatbed.
LARGER AWG numbers relate to SMALLER WIRE...
I think you have used the wrong wire
regards Joan
I try to make safe suggestions,You should understand the context and ensure you are happy that they are safe before attempting to apply my suggestions, what you do, is YOUR responsibility. Location Halifax UK
RE:
Yeah, I definitely did. Using 14AWG, it was still slow - but much faster than before. I might try 12AWG, but do you think there's a limit (safety wise)? Im assuming not
Thank you, regardless
RE: MK2S preheat Bed Thermal Runaway error - while temperature is increasing
Hi Leo,
I don't think there is a safety hazard using 12 gauge wire, the fuse on the motherboard is much lower rating than the cable rating.
BUT it might be difficult actually soldering 12AWG wire, onto the heatbed.
regards Joan
I try to make safe suggestions,You should understand the context and ensure you are happy that they are safe before attempting to apply my suggestions, what you do, is YOUR responsibility. Location Halifax UK