Need a little help with PID tuning.

[AndersE]

I have a roll of polycarbonate that should be printed around 300c, but can't get the PID under control.

I am using a E3D hotend on a K8200.

The temperature will either not stabilize or overshoot TOO much. I have even edited the firmware to 320c, original max temp was 280 in marlin i think.
Before reflashing of board i could not get over 280 until it shut off the extruder.

Now i can get up to 295, but the temp oscillates to much.

Have done the PID calibration with fan on max, but does not seem to be enough. Then if i try to heat without fan, the temp osc is WAY off.
Fan on= 270-310c if set on 295c. It takes forever to get it printing = 10.9.8.7.6.5.4.3.2.1 then it starts over.. 10.9.8 etc..

And even if max temp in firmware is set at 320 it warns and shuts off before it get over 305..

Any tips is appreciated..

[jimc]

In the firmware turn the pid max down. Its default to 400. Turn it down to 150. That limits max current to the heater and will get the over shoot under control so you can do a proper pid auto tune.

[AndersE]

Ahh, thanks i will try that..

[AndersE]

I can't find any max pid temp in the marlin config.. there is just the stuff about bangbang mode etc..

[jimc]

max pid should be in the config h file

[AndersE]

Ahaa, it got confusing for me as you said it would be att 400 original. But i realise all numbers are 8bit.

And my code does not look the same.

But i found it.. I will test diffrent max's to se how it does.

[jimc]

i found that in the communication window in s3d that the feedback for the extruder power you see there is half the # in the firmware. for instance on initial warm up of the hotend it would give me an @200 for the current level. when i changed it to 150 now it gives me an @75.