(Smoothieware)Cant maintain temperature after a print begins

[singhm29]

Hey all,

For some reason PID autotune on smoothieware has never worked properly for me. When I say that I mean I will Zero my bed, put my fans at full blast and begin the autotune. It will complete 3/8 give me what look to be reasonable numbers
Kp 41.7
Ki 2.427
Kd 175
I will start a print (1.0 layer height using a 1.2 nozzle at 250C at 1800mm/min) and with those settings within the first few seconds it will drop 4 degrees instantaneously after a print begins and dropping 10-15 degrees after the first layer completes. I get this is alot of material to handle but its as if the heater doesnt even attempt to remedy the situation. I ended up fudging the PID values to
Kp 85
Ki 2.427
Kd 80
This gave me an active response where while the temp would still drop 4 degrees to start the heater would fight back and be able to recover to 249-250 within a few minutes of the print.

I chalked this up to bad hot end insulation (combination of Kapton and Teflon tape) and a third party heater cartridge.

Fast forward to today E3D came out with their volcano sock so I finally got that and a new heater cartridge. Installed, ramped fans to 100 after zeroing the Z and commenced PID autotune.
Kp 44
Ki 1.608
Kd 301
Exact same behaviour with these values that were terrible in the fact that the temp would drop 15 degrees after starting the print. I ended up using my fudged PID numbers which work fine at 250 but hillariously in an effort to help interlayer adhesion and maintain print speed I decided to print at 265 and then got the same behaviour, 20 degree drop within the first few minutes of the print.
Kp 85
Ki 2.427
Kd 80

I dont get whats happening here, the next thing im thinking of is electrical noise? I have spade connectors as quick disconnects on my heater cartridge and the printer is fairly large so the distance to the control board is pretty long (2-3ft)

[cinpro]

well turn your fans off ( I know I know) and do a the PID, once that completes you can turn your fans on if you want. If you happen to have the Little MOnster then keep your fans below 50% until you get your hotend insulated. The fans are overpowering the hot end, esp if you haven't completed the PID.

[upsm]

When you start your pid calibration with fans on, does the hotend reach and hold the required temperature?
Autotune usually let it oscillate and calculate the pid indexes from the oscillation frequency and amplitude. IIRC you can graph the temp curve while smoothieware is doing the calculation, should give you clues how it behaves.

In any way, you want to insulate your hotend, that's needed more then a proper pid config