Temp Variance

[morgandc]

How much of a temp variance between target and actual should I bee seeing? I am just now starting to watch during prints, and I just saw 68c on the bed when the target was 60c. The hot end target is 220 and I have seen 216.

If this is not normal, any idea what could be causing it? I believe it started last night, but it could be I just became aware of it last night. Octoprint graphs it for me, so I now I am really aware of it

[mhackney]

Once it stabilizes 1° tops. As it heats up, it can overshoot (that's what PID tries to eliminate).

[morgandc]

So, really a person should preheat separately prior to sending a print to get past that overshoot if the surface temp is critical. Interesting, it looked solid after it came back down as it should.

[rurwin]

It will heat and cool differently depending whether it is melting filament. So it overshoots when pre-heating. If you tuned that out then it would be sluggish while printing; not what you want. But yes, the closer you can get it to working temperature before starting the print, the better. Except then it's a trade-off with issues such as oozing.

That's one reason to print with a perimeter; it primes the filament flow for losses from ooze and it lets the temperature settle down.

[mhackney]

@morgandc - Yes! In fact, preheat not only to eliminate the effect of that overshoot but more importantly, you want everything to equilibrate at temperature. For the big bed that takes at least 10 minutes, the hotend 5 or so. (these are safe numbers) As I stress in *almost* everything I write, consistency and predictability are über (not the transportation service) important! I've watch a lot of people turn on and attempt to print and not get the 1st layer to stick with an otherwise well calibrated machine and good temps. They get frustrated and start changing things when all they needed to do was go grab a coffee/beer/soda/single malt scotch and relax for a couple of minutes until the bed was stabilized!

[morgandc]

Well, something else appears to be going on as well

After doing a preheat to 260/60 the bed was rock solid for 10 minutes then decided to spike above target by 7c and return to target. The Nozzle has now decided to hover 1-6 degrees under target. I can up the target by 5 degrees and it plays the same game, just at a higher temp which means I am having trouble even starting a print. I think the problem is worse at a higher temp because I just switched from printing at 220c to 255c for PETG. Got a couple of prints at 250, but 255 and 260 won't even start printing as the temp never hits target.

[morgandc]

[morgandc]

Oddly enough at about 18 minutes it just gave up and started printing. There must be a timeout somewhere that says go for it?

[mhackney]

Is this a V3? It sounds like your power supply is running out of Umph (the technical term for Amps).

I'm not aware of a low temp "print it anyway" feature. That would be sub-optimal and potentially grind a lot of filament.

[morgandc]

Another spike on the plate.

[mhackney]

That's not normal, especially that large of a jump on the bed.

[IMBoring25]

That's weird. What are your bed PID settings? You also have a lot of noise that likely suggests a marginal connection somewhere in your hot end thermistor circuit.

[morgandc]

Default Rostock Max v3

[morgandc]

Since I connected Raspi last night, I was hoping that was involved....but no such luck. I removed it and when printing off the internal SD same issue.

[morgandc]

[IMBoring25]

Is it possible there's something else heating your bed at those times? Does any of your software chart the PID drive history?

[morgandc]

Issue occurs while printing from sdcard with nothing connected via USB.
220/60 set for pla seems stable.

[morgandc]

Still happening at higher temps. Next test is to try with the heated bed off.

[morgandc]

Seems more stable with the bed off, does that indicate power issues? Next test is crank the temp a little higher and see if it gets worse.

[morgandc]

@IMBoring25 I don't know of any way to get to PID drive history on either the Octoprint or Rambo. If you have suggestions I will look at them.

[morgandc]

The room is at 22c.

Running at 270c/80c there is a larger gap between set and actual so higher temp/power usage appears to exacerbate the situation. This can't really be a power issue however, because the both temps sort of stabilize above the previous lower set temps. I am completely baffled by this and have no idea where to go other than back to google and tech support on Monday.

Can anyone else reproduce this issue on their Rostock Max v3? You don't need to print or have high temp filament, just preheat will do it.

Thanks,
-Dwight

Image: 270c/80c

[IMBoring25]

I know Repetier Host has a chart if you can directly connect to the machine long enough to debug it. It's free as in beer but not as in speech, so depending on your personal feelings on the matter, there's that.

It does seem as though most of your hot end noise is associated with bed power, and especially bed PID. Do the bed power wires run near the hot end thermistor wires, especially anywhere they might run parallel to each other? It's less likely to be a critical issue since it doesn't appear to be due to an intermittent connection, which is what would have the potential to cause a runaway, but it isn't ideal.

[morgandc]

I am more than happy to download see what Repetier Host can tell me. Let me work on that.

On the noise, if you look at the 220c/60c chart it is really clean noise wise as well. This would tend to indicate to me something else is going on rather than noise being introduced with bed power.

Thanks for mulling it over, I am stumped at this point.

[morgandc]

set to 220/60 initially, holds temp nicely. Just before 45:00, I change to 260/60 and you can see that it never reaches temp. You can also see that it isn't running at full heat either.

[morgandc]

Zoomed in a bit more at 255c/60c over 5 minutes. You can see that it never hits temp.