What fluctuations in bed temperature are normal?
I received my i3 MK3S+ kit last week and finally finished building it Saturday. I've got about 20 hours of print time on it and all the prints I've done so far have been successful with no issues whatsoever. Though, I am noticing some fluctuation in my bed temperatures and I'm not sure if that's expected or not. I've done PID tuning for the bed and nozzle but it still seems the bed will fluctuate between 59.4C and 60.8C during a print job when set at 60C. It doesn't seem like much, but from the couple measurements from other MK3s I've been able to dig up online, the bed variation on those machines only had a fluctuation range of ~.6C.
Is this a normal range of fluctuation or do I have an issue? It's strange because I've run the PID test several times from a cold bed and every time the recommended values are different (I don't know much about the actual PID formula so maybe the changes are minute). One other thing I'm confused about is how far the bed and nozzle will overshoot their set temperatures during the initial warmup (and cooling down after the first layer for the nozzle). I thought the whole point of PID tuning was to accurately hit the set temperature and keep it stable.
One other thing I should note is that there is a still a small fluctuation of ~.3C that occurs even when the machine is completely cold just measuring ambient temps. Maybe I'm just overthinking this and hypersensitive thermistors make the issue seem more dramatic than it is...
RE: What fluctuations in bed temperature are normal?
Hi, you have to take in account also the regulation hysteresis along the set temperature. I this would be to small the oscilation around the set temperature would be much more intensive.
The PID constants are also dependent what is your starting ambient temperature and the target temperatur.
Nevertheless the bed itself provides a mass which can accumulate an energy so the temperture fluctuation on the thermistor location can be higher than the whole bed temperature changes.
even an old man can learn new things 🙂
Standard I3 mk3s, MMU2S, Prusa Enclosure, Fusion 360, PrusaSlicer, Windows 10
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RE: What fluctuations in bed temperature are normal?
Thank you, this does make sense and I'm aware the temperatures won't ever stay exactly at their set temperature when printing as filament is going through the hot end and the bed is moving back and forth. The amount of the fluctuations is just concerning to me.
I decided to revisit my printer this morning to check the issue when idle and I think the issue isn't with PID tuning but with the thermistors. My printer has been offline for over 10 hours and is in a location with a stable temperature (20.5C) and no draft. I would have expected the temperature being measured by the thermistors to be virtually constant, but I'm still noticing that both the hot end and bed temperatures are oscillating between 19.5C and 20.7C in OctoPrint, and I see the LCD screen on the printer itself fluctuating between 20C and 21C.
Why would such large fluctuations be occurring when the system is completely idle and ambient temperature is constant? I would expect very slight changes over time as the temperature of the room changes slightly, but with seemingly every 1 second polling interval, the temperature of the bed/hot end is going up or down by .4C-.7C.
