Hi
instead of repeating myself i will link to an issue i raised at marlin firmware
github.com/MarlinFirmware/Marlin/issues/5477
hope someone can help be figure what is wrong here
In addition to the hard *_MINTEMP and *_MAXTEMP limits, there is also thermal runaway protection in the PID to shut down any heater that fails to reach target temperature for some time period. I suspect that when your printer is running, the power supply is struggling to also heat the bed, causing the temperature to stay out of range for too long.
You could do a PID calibration and update your PID constants in the firmware. (http://reprap.org/wiki/PID_Tuning) This will make sure the PID has realistic expectations of the physical response characteristics of your printer. You may also want to think about getting a stronger power supply.
You can disable the PID thermal protection altogether by editing Configuration.h and commenting out the definition for THERMAL_PROTECTION_BED. This would verify whether this is the problem, but it is not a good long-term solution as it disables protection against a thermistor failure.
[code]//===========================================================================
//======================== Thermal Runaway Protection =======================
//===========================================================================
/**
- Thermal Runaway Protection protects your printer from damage and fire if a
- thermistor falls out or temperature sensors fail in any way.
- The issue: If a thermistor falls out or a temperature sensor fails,
- Marlin can no longer sense the actual temperature. Since a disconnected
- thermistor reads as a low temperature, the firmware will keep the heater on.
- The solution: Once the temperature reaches the target, start observing.
- If the temperature stays too far below the target (hysteresis) for too long,
- the firmware will halt as a safety precaution.
*/
#define THERMAL_PROTECTION_HOTENDS // Enable thermal protection for all extruders
#define THERMAL_PROTECTION_BED // Enable thermal protection for the heated bed
[/code]
Did you compile your own firmware?
Have you uploaded our firmware. What version of the Arduino IDE did you user?
When started this funny behavior?
“the power supply is struggling”
should 15V 30A not be enough?
Temps are stable if i enable them manual
Pid tune is done
Will try to disable protection on the bed and see if it makes any difference
“Did you compile your own firmware?”
No i used marlin firmware: github.com/MarlinFirmware/Marlin/tree/RCBugFix
“If you have uploaded the firmware with our version.”
If what??
“What version of the Arduino IDE did you user?” Latest of course: 1.6.13
When started this funny behavior? IT has always been there, i just got the printer for free as someone did not make use of it
btw. i’m right now testing repetier firmware to see if that made a difference
i also posted onmarlin forum but no response there.
If repetier works i have found the fault and will also load repetier on my other printer
Q: it seems that the bed does struggle a lot to get to even 60C degree
What is the max voltage that can be put in to the controller? 15V or 24?
I have read that 24V would solve the issue and using 24V directly would make things simpler instead of a SSR and messing with the wires to much
pid tune for the bed failed. max temp before timeout was 47 degree’s
will try and tune in steps of 5 from 45 and see if the max is still the same
So if i do a M303 P3 C8 S45
it should start Pid tune at 4 degrees
but on the temp chart in pronterface i see ver tiny noise spikes and it hovers between 46 and 47 degree’s
hmm…
had to hit reset as the temp got up to 50 degrees and i only called for pid tune at 45
could this be switching noise from the fet that controls bed power?
i will try bang-bang control for the bed and see how it goes
that worked far better
but it levels out at 55 degrees where i set it to 60
so that returns me to the question of using a 24V psu instead, but can the controller handle that? a Mega+Ramps combo can but maybe not the K8200 version?
it says that this is the schematic: reprap.org/mediawiki/images/9/9f/Schema_base.jpg
and if i read that correct it does have onboard 5V regulators to power itself, while steppers and bed etc are powered directly from the input?
and if i remember correct the stepper drivers does not mind 24V?
looked some more at the diagram…
if i use 24V i have to set the JPV to 5V so endstops does not use the power input but the internal 5V
and my bed would be getting 24V and my hotend would also
any bad things i have overlooked?
You should really start with the Velleman firmware you can download it here.
http://www.vellemanusa.com/support/downloads/?code=K8200
You should not use higher versions of the Arduino software the 1.0.6 you can download that from here.
https://www.arduino.cc/en/Main/OldSoftwareReleases#previous
the universal question of them all… why?
The firmware was modified for the K8200
Anything above Arduino 1.0.6 does not play nice with the K8200.
However you could just leave it the way it is and wonder why it doesn’t work right.
Think i will humor you and pick the last option and get it to work 
Enjoy