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bed struggling to get to temp or stay at temp

Posted: Thu Apr 19, 2018 9:03 pm
by n3rdglass
the last few weeks i've been having trouble warming up the bed, it takes longer than it used to and sometimes gives this error:

Error: heating fault on heater 0, temperature rising much more slowly than the expected 0.0°C/sec

i've also had a print fail because the bed couldn't stay at temp, gave this error:

Error: heating fault on heater 0, temperature excursion exceeded 15.0C

i've double checked the wires from Duet to the heated bed and they are firmly connected, could anyone offer some more diagnosis suggestions?

Re: bed struggling to get to temp or stay at temp

Posted: Fri Apr 20, 2018 11:15 am
by UltiBots
Have you made changes to your config file, upgraded firmware, added fans, changed room environment, etc...

Unless the heater has been damaged, it is not the problem. Verify its resistance with a multimeter it should be around 2.6 ohms depending on test location. If OK then I would focus on PSU and motion controller. I would ask on the Duet forum also.

Re: bed struggling to get to temp or stay at temp

Posted: Sat May 05, 2018 3:06 pm
by n3rdglass
no changes to the config file, no upgraded firmware, no changes to fans or room environment.

i measured the resistance to be at 2.6 ohms.

could you please be more specific on how i should focus on the PSU and motion controller? is it time to try a different power supply?

Re: bed struggling to get to temp or stay at temp

Posted: Sun May 06, 2018 6:49 am
by UltiBots
If and only if... you feel comfortable with this test... (I take NO responsibility for damage/fire/burns) you could wire the heater directly to the PSU 24v +/- terminals. You will need to MONITOR the heater and be READY to kill the A/C power to the PSU if the heater gets too hot. You will need an IR thermometer of similar to measure the heat (maybe even your hand but again NO responsibility). This test will determine if the heater or PSU has a problem.

Other things to examine is the thermistor, test for continuity and measure it's resistance. The resistance varies with temperature. I got 92K ohms at 75 Fahrenheit. Verify its connector is sound and the connection to the Duet is good.

If the heater/PSU test is OK then you will need to reach out to the Duet forum as they are more knowledgeable and have tons more troubleshooting experience with Duets.

Re: bed struggling to get to temp or stay at temp

Posted: Mon May 07, 2018 11:07 pm
by n3rdglass
thanks Brad. i should also point out this issue is intermittent. today i was able to print for around 6 hours until the bed quit heating and the print failed. does this help diagnosis at all? i understand how to wire the bed heater directly to the PSU, but what do i look for once i've done that? i have an IR thermometer, could you give me a little more direction on what steps i need to take?

i should also say that when the bed fails to stay warm enough the temperature is measured accurately, compared to my IR thermometer.

Re: bed struggling to get to temp or stay at temp

Posted: Wed May 09, 2018 11:43 am
by UltiBots
The more I think about it... If the Duet is not rebooting (loss of power), the issue is more likely Duet related as the heat bed is powered off the Duet and the Duet powered by the PSU.

I recommend asking about this on the Duet forum. The Duet guys have a much larger knowledge base and can provide better troubleshooting support for the Duet.

Alternatively maybe you can you borrow/find a 24v 300+ watt PSU for testing.