If I set temperature say 220 °C, printer heats up to it and it only varies +/- 0.5 °C under non operating condition. But if I start a print, there's a shift of +/- 15 °C.
I've already auto tuned PID parameters and when I run M503, the printer shows the updated PID values.
What could be the reason?
Electronics details:
There could be a number of reasons for that behaviour:
Please check following items:
Dropping hot end temperatures can be caused by the filament cooler blowing too much cold air onto the nozzle, or a too high of a print speed so that the nozzle is cooled by the filament (in combination with a heating element that cannot heat that fast to compensate).
To rule out the PSU you could try measuring the voltage of the PSU before and after powering the heat bed, if it drops dramatically when the heat bed starts change the PSU.
My problem was like yours and after several test I found bad PID tunning in heated bed disturb hotend temperature process.
Before heated bed PID tunning:
When I fixed PID values for heated bed everything works like a charm :)
Can you also show a "power output" graph (or something like that, which show PWD duty cycle output to the hot end)?
Have you noted any relation between temperature raise and fall and the printing position?
Looking at graph I can only suggest the heating is suddenly stops and then the same sudden resumes. It looks like you have a loose wire connection to the heater. When head is starting to move, it makes disturbance for the wiring, so heater occasionally stops to work. There are usual two weak points: first it is where cable is connected to the board. Check is connector heated? Are any noises/sparks from there? Another part: it is just at the point where wires going into the hot end. If wires are not secured to the printing head, then during printing those place experiences a lot of bending, which makes it weaker over the time.
Hello I have had the same issue, fluctuating thermistor temperature, all of them. Discarding the board, and accessories setup (loose the heater, thermistor and so on) the problem was on the PSU. When I have opened the PSU and touched gently all the parts then closed again and connected it to the printer: temperature readings were stable egain, however just for a time.
Fluctuations of temperature due to heating have in general low frequencies due to the heat transport phenomena in material such as plastic and metals especially if the amount of metal material is of the order of 100 grams.
Changes over the time with supplied power of about 500 watt over 100 grams of metal and plastic flow of a fewer grams per minute, seldom, cant cause temporal fluctuations in frequencies of the order of electrical fluctuations. It's possible but not in 3D printing case.
off, please explain why the bed temperature increased? E.g. did you shut of the bed prior to making the screenshot? $\endgroup$