PID tune bed.. overheats regardless of power used.. missing something?

dintid

I know I know, but I really have tried to search and read here on the fora, so not just posting blindly

Trying to PID-tune my heated bed.
I come from Marlin and then Smoothieware where I issue a Gcode command and it runs, say, 6 cycles and I get some parameters.

In RepRapFirmware I run a M303 (target heater) (target temperature). Default power is 50%. Problem: overheat.. ok, but wasn't this why I started the tuning? To make my machine figure out how not to overheat?

I have gone through P0.4..0,2 but it keeps overheating, when going for 100c.

I tried inserting an image, but is it correct when I assume we can't upload images to the forums? So heres it goes in "code" form.
Top is newest

[[language]]
19.08.25M303
Heater 1 tuning failed
19.03.46Auto tune of heater 0 with P=0.20 S=100.0 cancelled because temperature limit exceeded. Use lower P or higher S in m303 command.
18.52.42M303 H0 P0.2 S100
Auto tuning heater 0 - do not leave printer unattended
18.47.53Auto tune of heater 0 with P=0.30 S=100.0 cancelled because temperature limit exceeded. Use lower P or higher S in m303 command.
18.42.00M303 H0 P0.3 S100
Auto tuning heater 0 - do not leave printer unattended
18.33.15M303
Heater 1 tuning failed
18.33.07Auto tune of heater 0 with P=0.50 S=100.0 cancelled because temperature limit exceeded. Use lower P or higher S in m303 command.
18.30.12M303 H0 P0.5 S100
Auto tuning heater 0 - do not leave printer unattended
18.29.35M303
Heater 1 tuning failed
18.26.52Auto tune of heater 0 with P=0.50 S=60.0 cancelled because temperature limit exceeded. Use lower P or higher S in m303 command.
18.26.03M303 H0 S60 C3
Auto tuning heater 0 - do not leave printer unattended

I guess I can continue dialing power down, and run it at like 5% but that defeats the purpose of having a 500w AC heater under my 5mm aluminium plate!

Am I missing something here?

dc42

Try 0.1. The power level you set in M303 is only used for tuning purposes.

I have it on my list to implement a different tuning mechanism that doesn't need you to set approximately the right power level first.

StephenRC

Either lower the P and/or increase the S. For my 800w McMaster 110vac powered bed heater I used: M303 H0 P0.2 S140
I do have a thermal fuse installed and that takes care of killing the bed heater if anything goes haywire.

dintid

@dc42:

Try 0.1. The power level you set in M303 is only used for tuning purposes.

I have it on my list to implement a different tuning mechanism that doesn't need you to set approximately the right power level first.

It would be nice as I literally spent 1 hour 5 minutes PID tuning my bed. 2 failed attempts and the last one that succeeded took just shy of half an hour.

It would be nice if use didn't have to type the M307 H0 to see the result, but just show it right away… maybe even printout a line for the user to insert in the config.g file

I do not consider my 500w AC heater for overpwered. It's heating a 5mm thick UM2 sized aluminium plate, but warned about it being dangerous.

@StephenRC:

Either lower the P and/or increase the S. For my 800w McMaster 110vac powered bed heater I used: M303 H0 P0.2 S140
I do have a thermal fuse installed and that takes care of killing the bed heater if anything goes haywire.

Yea, I ended up having to run it at 0.1 It failed at 0.2
Mine is a 500w 220vac heater I used for 5mm aluplate on um2 sized bed (20x22 ish)

dc42

The 1.18beta firmware no longer requires you to guess an S parameter when auto tuning. In 1.17 and later you can use M500 to save the M307 parameters to config-override.g without having to type them in.

dintid

@dc42:

The 1.18beta firmware no longer requires you to guess an S parameter when auto tuning. In 1.17 and later you can use M500 to save the M307 parameters to config-override.g without having to type them in.

I'd rather have the settings in my config.g file, as these are my basic from the go settings. I'd hate to start out with wrong values in there, and then have to use an override from the get go, or am I just missing out on a great feature?

dc42

You can use M500 to save them to config-override.g, then use the System Files Editor in DWC to cut-and-paste them to config.g. The config-override.g file is only used if you have M501 (or M98 Pconfig-override.g) in your config.g file, but regardless of
whether you do or not, M500 will save values to config-override.g.

dintid

I know, I just tried to share my views on how it might be improved

You allready have printed message for user on what to do to view the result. That message could be replaced by the actual codestring resulting from an M500, which the user could either insert manually into config.g, or be instructed to type M500 to have it placed in the config-override.g file

dc42

The 1.18 firmware series does prompt you to run M500.