Unstable hot end temperature?

Dreide · Post by **Dreide** » Mon Jan 27, 2014 12:56 pm

Does this hot end temperature curve look normal?

My prints look fine so far, but I am a little bit worried by the high temperature variation.
Unfortunately I did not closely watch the temperature curves when I got my Felix 2.0 because I went pretty much right away to SD card printing. So I cannot tell how it looked like when the Felix was new. After discovering this behavior, I watched it for about 20h of printing time now - normal prints, nothing special, rather moderate printing speed, different layer heights etc.
The strange thing is that the temperature control is accurate to something like ±1°C when printing small parts where the printer slows down so as to not exceed the minimal layer printing time. Also, the curve is smooth when there is no printing going on. However, I cannot force wrong temperature readings by manually moving the print head or jiggling the thermistor wires. The reported temperatures for the head and the bed are the same when cooled off.

Bachgassenbande · Post by **Bachgassenbande** » Mon Jan 27, 2014 5:51 pm

Wow you had a hughe drop of 20°C in your curve;
Normally for me is about max 8°C dropping when starting a new layer.

Is your thermistor still locked in place?

Makron · Post by **Makron** » Mon Jan 27, 2014 6:07 pm

I have a Straight line..

andrewsi · Post by **andrewsi** » Mon Jan 27, 2014 6:55 pm

Are you using the standard Marlin firmware? It has a built in code you can call from a terminal or repetier host to have it try to work out optimal PID values. You could let it run that, then print something to see if it's any better. If it is, you can write the new values to the EEPROM so they're saved.

Dreide · Post by **Dreide** » Mon Jan 27, 2014 8:08 pm

Bachgassenbande wrote: Is your thermistor still locked in place?

I cannot move the thermistor by hand at least. But it sticks out a bit and I don't know whether this is supposed to be this way.

Dreide · Post by **Dreide** » Mon Jan 27, 2014 8:10 pm

andrewsi wrote:Are you using the standard Marlin firmware? It has a built in code you can call from a terminal or repetier host to have it try to work out optimal PID values. You could let it run that, then print something to see if it's any better. If it is, you can write the new values to the EEPROM so they're saved.

I tried to recalibrate the PID values but there was only a small effect if at all.

Dreide · Post by **Dreide** » Mon Jan 27, 2014 8:16 pm

Makron wrote:I have a Straight line..

Wow! Even if I stop printing it looks not as flat with my printer. I suspect a bad thermal coupling between the thermistor and the hot end with my printer.

Bachgassenbande · Post by **Bachgassenbande** » Tue Jan 28, 2014 9:02 pm

Here is just a snapshot of my temperatures;
you see the influence when turning on the 2.fan

Dreide · Post by **Dreide** » Tue Jan 28, 2014 9:47 pm

Bachgassenbande wrote:Here is just a snapshot of my temperatures;
you see the influence when turning on the 2.fan

So the first part shows the behavior when printing without 2nd fan? And after that, was the fan running at different speeds (perimeter vs. infill), or where does the slow oscillation come from?

Bachgassenbande · Post by **Bachgassenbande** » Tue Jan 28, 2014 11:39 pm

1st part without fan (1st layer)
starting with the second layer the perimeters and infill was cooled with diffrent fan speeds.
As i printed two small identical parts....

Just printing a large part without 2nd fan ==> Temperature is stable +/-1°C not visible in the temp chart

Unstable hot end temperature?

Unstable hot end temperature?

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