I have this on GitHub but it seems like the guys over there want to make sure this is a Klipper issue first before reporting a bug so I will open a thread here to discuss it
I have a problem that I can’t understand why it is happening nor able to solve!
If I am heating the nozzle and the bed to a target temperature and If the bed reached its target temperature while the nozzle is still heating up there is nothing until now wrong but as soon as the nozzle reaches its target temperature, the bed temperature suddenly jump like 3 or 4 degrees up without any reason and stay raised for too much time like 1 minutes or so and start gradually decrease until it reaches its target with in other 3 or 4 minutes.
One thing I noticed that when this happens, the SSR(Solid state relay) does not really work at that point (when the temp. jumps)
but it keep trying to work later if the temp. start decreasing which makes it goes up again and this happens for the next 3-4 minutes until it gradually become stable
One thing I am doing to avoid this is to start heating the nozzle and wait until the temperature become stable and start heating the bed after that.
Of course because of that behavior the print job does not start until bed temperature is stable
I tried to make PID tuning for both the bed and the nozzle several times before but it does not help
I though it might be the Arduino 5V source is not stable and have noise so the ADC does not have a clean reference, so I changed the power supply to better one but I still have the same issue
I just recently moved from marlin and I was using it with my printer for several years and never had such an issue before.
I am using 220v 750W silicone heater for 300X300X4 mm bed and 60w custom nozzle.
There is one thing I recently noticed while I was trying something today, I have found this issue also even if I am only heating my nozzle and the bed is not heating up the bed temperature will also raised by may be 2 or 4 degrees!
I made more tests and found that this issue happens also while printing.
If I raise the nozzle temperature while printing the bed temperature will be raised even if it was stable before
Also If I lower the nozzle temperature the bed temperature will change again.
From your description, it sounds like a wiring, voltage, or grounding issue. I’d double check all the wiring and look for any foreign objects on/near the control board. You may also want to look at reducing the max_power settings of the bed/nozzle as the heaters may be drawing more power than desired. Finally, double check you have the right temperature sensors defined
I am using ramps1.4 and I am using solid state relay with 750w silicone heater with NTC 100K beta 3950 sensor and I am using for the nozzle PT100 with MAX31865
I have already double check every thing before and as I have mentioned this setup was working just fine with Marlin.
The only thing that have been add is the Raspberry pi!
This issue is only happening when a change in the nozzle temperate is going to end as I have descripted before
I have been busy for a long time but I came to a conclusion that there is a problem with the 5V reference voltage being used by the Mega board and since the VREF is being taken from the 5V supply rail and if the supply rail is not clean and stable it would definitely affect the ADC reading for the BED NTC sensor
I took out the 5V DC_DC converter and checked its output and guess what, it was not clean at all.
I added LM338 for the pi and lm2940t-5.0 for the mega and the problem is now gone!