Bed Temp Happy Underachieving

[glassrod85]

Sorry for all the noob questions - I swear i spend a long time searching/reading...

I'm having an issue where my filament profile has a bed target temp. I press print. Bed starts heating:
Target 90C
Actual: 88 +/- 0.5
It will sit here forever! like literally waited 20+ minutes. Print won't start because bed hasn't hit 90C.

So then I go in and change filament bed profile to 100C and within 2-3 minutes.
Target 100C
Actual: 97 +/- 0.5
Print won't start because bed hasn't hit 100C.

No changes in ambient cooling during this. This would imply it's not a bed heating capacity issue. It just seems that code seems happy outputting the same current during ramp even though target temp not achieved.

So far the only way I get prints is by manually preheating the bed above the filament target temp. Then pressing print and having it drop to temp to trigger start.

I know during setup we had to calibrate the response of the hot end. There seem to be similar parameters for the bed but we never were instructed how/when to calibrate it. Can you? Would that help?

Any ideas?

[teoman]

Yeah, there is a calibration for the bed aswell. It is very similar.

Try to find the old manual.

Have a look at PID control in wikipedia to understand why it is doung ehat it is doing.


I am on mobile at the moment so cannot digupp the gcode for you.

[glassrod85]

Thanks, going to try this from a wiki once my bed cools:
PID autotune
If you are using PID then you should run autotune to make sure it is correctly calibrated for your bed.

M303 E-1 C8 S90 //this will run autotune at 90 degrees, for 8 cycles

[glassrod85]

Nope, it's:
M303 P1 C8 S90

This hopefully will be added back into the user manual.

apparently a known issue since Oct. '15
http://forum.seemecnc.com/viewtopic.php?f=77&t=8960