I could use some help: heatbed thermal runaway, but only at ABS temps
Hi, I could use some help. I'm troubleshooting a heatbed thermal runaway issue on my prusa mk3 i3. When I print ABS, The bed can't manage to keep > 100 degrees C. PLA and PETG prints fine.
Below is a picture of the problem: it is 100% repeatable , and the print fails at about the same time each print:
Here are the things I tried:
1. printed with anything but ABS ( bed temp < 100) : works fine
2. updated firmware to latest: i'm on 3.10.1
3. tightened bolts leading to heatbed.
4. after 3 didnt work, replaced the heatbed wires with larger guage wire that's more flexible, and really snugged the lugs doen
5. checked thermister-- it appears nicely fixed to bottom of bed
6. set temp of bed to 90 degrees and moved bed front/back slowly and quickly; no dropouts: display reads 90/90 constantly with no issues
7. repeated above at 100 degrees
8. unplugged and re-plugged thermister connection onto main board
9. wiggled cables as print was happening about the time i expect it t fail: no effect.
10. changed print settings to 105/105.
11. I am printing in an enclosure. tried with the door open and closed
The printer never fails to make startup heat, and always fails at about t=4 minutes with a heat bed error. I've also observed that the failure is always smooth like in the picture: it loses temperature slowly 1 degree at a time.
Based on the fact that the temperature is not keeping up, and that the bed always makes initial temp, I believe this is a power problem, not a thermistor problem. Could it be that the power supply is struggling/failing? Does anyone have an idea what to try next?
RE: I could use some help: heatbed thermal runaway, but only at ABS temps
UPDATE: heatbed settings of 100/100 appear to work: the bed can keep up. Though, of course then i dont get great bed adhesion
RE: I could use some help: heatbed thermal runaway, but only at ABS temps
that suggests that your printer is struggling to achieve the desired bed temperature within a given time.
Is your power supply providing 24 volts? (My Mk1 printer had this problem, and the power supply voltage was low, raising the power supply output voltage sorted that problem) (that was a 12 volt power supply giving out 11.2 volts)
can you see 24 volts on the heatbed terminals (at the heatbed end of the wires) during heating?
If not ,Could you check the screw connections on the power supply, the einsy and the heatbed. looking for discolouration of the components, there may be a loose connection, or a faulty crimp, or a failing wire
the mosfet on the einsy could also be faulty but that is way less common, and much harder to confirm.
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: I could use some help: heatbed thermal runaway, but only at ABS temps
@joantabb thank you for this idea!
I measure 23.5 volts at the heat bed terminals with the bed heating (set to 90 degC).
I didn't mention it, but i also have the power supply outside the enclosure . This means that the temps getting to the supply is eliminated, but of course that means there are other wires in the mix that are possible culprits.
I am confident in the wiring between the einsy and the heatbed-- i just re-did that today. I think its either a dying supply or a wiring problem. Any ideas how i could figure out which it is? Insufficient current to the heat bed sounds like partially broken wire or 'failing component somewhere'.
RE: I could use some help: heatbed thermal runaway, but only at ABS temps
what wire did you use for the longer power supply wires?
16AWG is what prusa use,
14AWG would be better with good quality crimps connectors on the ends and no joints in the middle.
If your power supply is a silver one, there should be a trim pot on the side of the connector strip, under the bottom cover. you could consider trying adjusting that up to say 24.5 volts
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: I could use some help: heatbed thermal runaway, but only at ABS temps
Those are good questions! There are no joints in the middle, but i'll check the gauge. there's defintely an adjustment in there.
Thanks for listening and helping, I'll poke around
RE: I could use some help: heatbed thermal runaway, but only at ABS temps
try doubling the cables and see if that helps.
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