PID tuning to the wrong temp! (no replies)

Hi all,

I am having an odd issue with my hotend that comes and goes.

Printing ABS at 225, so i ran the PID autotune (M303 S225) and got....
#define DEFAULT_Kp 15.84
#define DEFAULT_Ki 0.51
#define DEFAULT_Kd 123.51

I entered these into my firmware and uploaded it.

BUT, when i set the temp via pronterface to 225, the current to my hotend switches off (@0) at 215.
Admittedly, it is very good at keeping at 215, but i need it hotter.

I had a look through the firmware and it seemed an odd coincidence that my PID functional range was set to 10
#define PID_FUNCTIONAL_RANGE 10

So i changed it to 8 - #define PID_FUNCTIONAL_RANGE 8 - and guess what happened.

My hotend peaked at 217!

I thought the functional range was the band inside which PID operated, outside it was PID max.

So shouldn't it max up to 215, then continue to climb up to 225?

I could set it to zero, but that would just be bang-bang wouldn't it?

To further complicate things i have had limited success using M104 S225 to fix the temp, but not always.

Does anyone have any ideas what is going on?

Thanks CT