PID'd bed keeps failing on heat up

Phaedrux

Thanks for the details. I've noticed a few faults like this myself in recent firmware.

jay_s_uk

@phaedrux I think it needs some sort of "soak" time, that could be configured, that would allow thicker beds to come up to temp before the PID tune is started.

cncmaker

@kr15_uk I had the exact same issue then i switched to a new thermistor and the problem stopped.

Now im getting the opposite error on my hotend ....
lol

Tinchus

I can report a very similar behaviour regarding heated chambers. PID tunning works, the tunning completes. But then using the reported values, heating always fails with the same error you have.
This behavour in my case started with 3.4 firmware, with old style PID it was working ok, so I guess the new PID model is not having a happy time with very slow heating elements?

Norder

@jay_s_uk said in PID'd bed keeps failing on heat up:

@phaedrux I think it needs some sort of "soak" time, that could be configured, that would allow thicker beds to come up to temp before the PID tune is started.

I have an 8mm aluminum plate over the silicone heating mat.
The thermistor is in the middle of the silicone heating mat.
The silicone heating mat is insulated at the bottom with a 10mm cork plate.

I don't think an additional warm-up time for the aluminum plate will have any effect or change anything in the measurement result !?
Except the thermistor is a bit away from the heating mat, which I have never seen before.

Google Translate
----- Original Text -----

Ich habe eine 8mm Aluplatte über der Silikon-Heizmatte.
Der Thermistor ist in der Mitte der Silikon-Heizmatte.
Gedämmt wird die Silikon-Heizmatte nach unten mit einer 10mm Korkplatte.

Ich denke eine zusätzliche Aufwärmzeit für die Aluplatte wird nichts bewirken bzw am Messergebnis etwas ändern !?
Außer der Thermistor ist etwas vom der Heizmatte entfernt, was ich so aber bis jetzt noch nie gesehen habe.

Norder

@kr15_uk said in PID'd bed keeps failing on heat up:

...it has 80w super volcano like heater cartridge in the block bellow the bed

A heater cartridge under the bed ?
I would like to see a photo of that.

Did you also specify the correct value for the thermistor in config.g, such as M308 S0 P"bedtemp" Y"thermistor" T100000 B4138 ?

Google Translate

----- Original Text -----

Eine Heizpatrone unter dem Bett ?
Davon würde ich gerne mal ein Foto sehen.

Hast Du denn auch den richtigen Werte für den Thermistor in der config.g angegeben, wie zB M308 S0 P"bedtemp" Y"thermistor" T100000 B4138 ?

rexx

@tinchus same here.. did you ever find out how or just buy an old duet2 and dont update it??

kr15_uk

@rexx you can downgrade firmware quite easily, haven't downgraded my one yet though, I believe in good ppl fixing the issue at some, naive - perhaps!
For the time being I've added couple of lines into my start gcode to do "staged" heating up which works well for me.
M140 S40
G28
G1 Z140 F300
G28
M140 S50
G28
G1 Z140 F300
G28
M140 S60
....

It goes to 40c fine 1st go but then needs extra "dwell" time so by adding slow moves gives that extra time... Not great by no means but oh well, it's temporary right?! Right??!

gloomyandy

@Tinchus @rexx @kr15_uk If you are having heater problems please see this post by @DC42: https://forum.duet3d.com/post/291170

He provides details of what he would like you to do to help him work out what the problem is....

rexx

@gloomyandy
on it i will have a look

thank you

Tinchus

@gloomyandy Wil do, Im pleased to help