Lack of Temperature Control at High Temperatures

[carotti 0]

 

I have been trying to get quality prints with ABS for the first time and have noticed that Marlin U0.9.3.1 does not correctly regulate the temperature of the hot end if the set-point temperature is too high. I have included two charts that show the effect. For the set-point of 210 degrees, the temperature is correctly regulated with some ripple as expected. With the set-point of 272 degrees, the temperature rises to the correct aiming point, reaches it but then drops back again. Does anyone know what the maximum set-point temperature is and if there is a work-around?

[Daid 306]

Tried the newer RC2 marlin with PID?

http://daid.eu/~daid/marlin_build/

 

[carotti 0]

Thanks Daid for the fast reply. I have now tried "Build Me Marlin". This is really good - you really are helping me run before I can walk!

In short, as far as I can tell, PID does the same thing but for very good reasons. What I can see now is that the initial rise in temperature overshoots the setpoint of 272 such that the extruder maximum temperature default of 275 is exceeded (277 reported), so the heater is turned off and the temperature correctly falls back. I suppose I could reduce the Kp value to reduce the overshoot, but then the whole dynamics of temperature control are altered in ways I will not understand. *my internal alarm bell rings*

To summarise: This has taught me a lot about building Marlin, using GitHub, PID and made me question the sanity of using such a high temperature in the first place even for ABS.

[Daid 306]

To summarise: This has taught me a lot about building Marlin, using GitHub, PID and made me question the sanity of using such a high temperature in the first place even for ABS.

ABS needs a higher temperature then PLA. But remember, around 300C your PEEK will start to meld. Which is kinda very extremely bad for your machine.

[erikzalm 0]

Hello Carotti.

The last Marlin version has a PID tuning feature. It is very experimental but it works on my Ultimaker.

You can start it with M303. It will display the temperature. After a few temperature cycles it will display Kp, Ki and Kd values.

You can use these values in the configuration.h file.

[carotti 0]

But remember, around 300C your PEEK will start to meld. Which is kinda very extremely bad for your machine.

No kidding! OK, after some experimentation with ABS I would now say that the highest reliable set-point temperature that does not trip the heater shut-down is around 268 degrees. I am satisfied that with this temperature, I can get ABS to stick together nicely. For the record, my heated platform is measured at 120 degrees and the FAN IS OFF. Altogether I now have some satisfyingly un-warped ABS prints for the first time even with 100% fill. The build surface is currently blue tape brushed with several layers of ABS dissolved in Acetone.

[carotti 0]

Hello Carotti.

The last Marlin version has a PID tuning feature.

Thanks Erik, I will explore this if I have to push the temperature boundary any higher and get tighter regulation. I am still a new user, so am trying to avoid as many experimental features as possible but I can definitely see the benefit if it reduces the temperature variation at high set-point values. Is it intended to run 'on the fly' or to derive better Kp, Ki and Kd values for each particular Ultimaker?

[carotti 0]

Hi everyone, just to provide some positive closure to this one....

I am now using Daid's excellent SkeinPyPy Beta4 with the default PID settings and Marlin firmware that it updates to when first run. I am getting a very tight +/- 0.5 degree now on the temperature control.

 

Many thanks for the help!

Dave.

[c-ernst 1]

You might want to dial back the fan too. I had to run at crazy high temps until the fan was turned down. In some cases I run the fan at 25%.

Chuck

[joergen 2]

You might want to dial back the fan too. I had to run at crazy high temps until the fan was turned down. In some cases I run the fan at 25%.

Chuck

The fan is still mission critical to cool the printed object, and you need the ability to crank it up to 100% fan speed. limiting the fan, only because your head isn't insulated, isn't the right solution. one way around it is printing Owen's fan (

http://www.thingiverse.com/thing:13625

still the best fan duct there is), which avoids blowing cool air onto the heater. if that isn't enough, insulate the head with fiberglass sheets, or better silicone foam.