Klipper MCU disconnect when changing glass bed for new print

General Discussion
1

Basic Information:

Custom Delta
MCU: STM32H723VIT6 / Printerboard: BTT SKR 3 EZ Host: core i7 NUC

KLIPPY.LOG (4.6 KB)

Hi all,

Hope someone here can help me with this.

I am wanting to swap out glass build plates at the end of prints so I do not need to go through another preheat cycle each time.’

My issue is that when I put a new plate on the bed temp drops rapidly (as would be expected) causing an error to be raised and a reset required…
Heater heater_bed not heating at expected rate
Once the underlying issue is corrected, use the
“FIRMWARE_RESTART” command to reset the firmware, reload the
config, and restart the host software.
Printer is shutdown
I see there is verify_heater section available in config but I would be most appreciative for some guidance on how I could apply this while still maintaining safety in the event of a dangerous fault.

With thanks
Brett

2

Hello @brett_l !

As the new glass bed is cold, and is thick, it has to be heated as well.

Let’s say the new glass bed is about 20°C. The heated bed is at 60°C.
When the glass bed gets on the heated bed, the heated bed is cooled down.
So you get the error:

12:23:19 Heater heater_bed not heating at expected rate
See the 'verify_heater' section in docs/Config_Reference.md
for the parameters that control this check.

because Klipper expects the bed at 60°C and has to pump all power into the bed. It can not be on 60°C from now to then.

This is a matter of thermal mass:

3

You need to experiment with max_error: 120 from the [verify_heater] section in order to find your balance for your hardware.

The “just right” value depends on many factors, e.g. ambient temperature, thickness of the glass, power of your bed etc.

Note it is a cumulative error, e.g. if your bed is 3 seconds 20°C below target, then this error counter would be at 60.

4

Thanks Sineos,

So if I understand correctly, if a new plate causes a 15 degree drop and it takes 60 seconds to recover back to set temp then I would use a value of 15x60 = 900 , or 15 x 30 = 450 for a 30 second recovery?

5

Unfortunately, a bit more complex, since your error gets smaller every second since it is heating.
Lets assume it takes 5 seconds to recover a 15 degree drop:

  1. Second 1: 15 degree to target
  2. Second 2: 11 degree to target
  3. Second 3: 8 degree to target
  4. Second 4: 5 degree to target
  5. Second 5: 2 degree to target
  6. Second 6: 0 degree to target → Back on target, counter gets reset

Total Error: 41

Don’t make it overly complicated: Set the error margin to 140 and simply try it. I would guess that not much is missing.
In case of a “real” problem, the error typically accumulates fast and if Klipper reacts on it within 5 seconds or within 10 should not cause your home to burn down or your dog being abducted by aliens.

6

Ahh,I understand now. Thanks for your assistance. Much appreciated.

I don’t have a dog to be abducted by aliens but have a Cockatoo instead which they may find more interesting. Anything to avert that is best practice in this crazy world :slight_smile:

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