PID control only running at 50%

Hi all,

I have searched for a solution on this but cant find anything.

I have PID set on my reprap running Marlin with a Makergear hot end.

The problem i have is that the hotend will not run any higher than @128 (50%), not 256 (100%)and so the temp drops when i extrude even though my settings are....

#define PIDTEMP
#define PID_MAX 256 // limits current to nozzle; 256=full current
#ifdef PIDTEMP
//#define PID_DEBUG // Sends debug data to the serial port.
//#define PID_OPENLOOP 1 // Puts PID in open loop. M104/M140 sets the output power from 0 to PID_MAX
#define PID_FUNCTIONAL_RANGE 10 // If the temperature difference between the target temperature and the actual temperature
// is more then PID_FUNCTIONAL_RANGE then the PID will be shut off and the heater will be set to min/max.
#define PID_INTEGRAL_DRIVE_MAX 255 //limit for the integral term
#define K1 0.95 //smoothing factor withing the PID
#define PID_dT ((16.0 * 8.0)/(F_CPU / 64.0 / 256.0)) //sampling period of the temperature routine


What am i doing wrong?

Thanks CT

I'm having the same issue. Haven't figured it out yet.

I think this should be posted in the firmware section though. I'm not sure we're going to get an answer here.

Been wondering the same thing, I am also running Marlin.

So after reading your post I put my osciloscope on the hotend resistor, and @128 actually means 100% at least on my machine.

So if your hotend drops in temperature @128 (100% dc) you need to either put in a smaller resistor, print slower, or raise the supply voltage a bit, ofcourse staying within the limit of the electronics.

Thanks Ralf,

Simple version....
It turns out that it is a measure of the PWM activity as a function of 128ths of a second.
So 128 is always on, 64 is on half the time and so on.

Thanks Chase.