PID calibrated, but won't hold temp in real life  

Re: PID calibrated, but won't hold temp in real life

Not to worry, it seems to have magically fixed itself for no apparent reason in the middle of a print 🙄

Re: PID calibrated, but won't hold temp in real life

I keep having the same problem crop up. Prints fine then drops 10 degrees below target temp. If I manually increase the temp by 10 degrees as a target then the temp will raise by 10 but not actually reach the target number. It comes and goes. The problem is across different filaments also.

I Dunno,

Neal

Re: PID calibrated, but won't hold temp in real life

I have exactly the same poblem.
It has started after I tuned PID temp.
before that I had no problem at all.
To repeat the problem is:

Print starts off at 215*C. After 3 layers as the fan starts the temp is now changed to 210, But nozzle temp falls by 10*C and is now maintained at 200. I can increase the temp to 215 but it is then maintained at 205.

I have printed this part in the morning with the same Gcode and there was no problem.

Re: PID calibrated, but won't hold temp in real life

I have the same problem.
I don't think I've ever done any PID autotune

Printed a test slab (20x30mm) in Generic PLA at "0.20mm FAST MK3"
First layer prints fine at 215C, then fan starts and 2nd layer begins at 210C, but temperature drops to 199C within 10 secs.

To investigate, I adding a pause of 3 mins in the gcode after the "M104 S210" temperature set command, I added: G4 S180

Temp is as follows after fan starts: (this is during the pause, i.e. not printing)
Secs Temp
0 215
10 200
30 203
60 207
80 210
...

Then when the print resumes the temperature is held OK at 210C within a degree, so the problem is not due
to printing too fast for the nozzle heater to keep up.

So... it looks like the PID control is taking about 80 seconds to re-adjust after the fan starts.

This was causing the 2nd layer of my print to not adhere to the 1st layer very well.

Yours,
TonyWilk

Re: PID calibrated, but won't hold temp in real life

Decrease the fan speed a bit in the profile. Especially with PLA profile, where max fan speed is 100%. I set max fan speed to 70% and the drop after fan start is smaller and temp. is more stabilised.

M.

Re: PID calibrated, but won't hold temp in real life

I didn't want to reduce the fan speed, just fix the erroneous drop in temperature when the fan starts.

Without having mess about with the PID values, I've effectively fixed the problem by adding some custom G-code
( I'm using Slic3r Prusa Edition 1.41.1)

;AFTER_LAYER_CHANGE
;[layer_z]
{if layer_num == 1}; at start of second layer
G1 Z3.0 E-0.1 ; move up a bit, retract?
M104 S{temperature[0]} ; set temp
G4 S30 ; wait for 30 secs for cooling
M109 S{temperature[0]} ; set temp and wait for it
G4 S10 ; another 10 secs for temp to stabilize
{endif}

It adds a bit of a delay, but I needed that to wait for the nozzle temp. to drop from 1st layer 215C to below 210C
so the M109 'set temp.; and wait' then works.
This works fine on the test prints I've done, hopefully it should work for all prints.

Alternatively, I suppose you could add custom g-code to set the fan speed to 'ramp up' over the first few layers.
e.g. NOT TESTED THIS !!!

{if layer_num == 1} M106 S50 {endif}
{if layer_num == 2} M106 S100 {endif}
{if layer_num == 3} M106 S150 {endif}
{if layer_num == 4} M106 S200 {endif}
{if layer_num > 4} M106 S255 {endif}

Yours,
TonyWilk

Re: PID calibrated, but won't hold temp in real life

Any help much appreciated.

Check this thread: https://shop.prusa3d.com/forum/general-discussion-announcements-and-releases-f61/-howto-pid-calibration-your-way-t18479.html

Either more aggressive PID settings or the heater block sock will help.