pid_i_max adjustment - nozzle wouldn't heat properly

my March reprappro Huxley's nozzle will now finally warm to 205 for PLA when requested because I adjusted pid_i_max in configuration.h from 80 to 130. Before I did that it would stick at 194-196 and I would have to pretend to pronterface that I was using ABS e.g., request 250 before it would get hot enough.



However, while I am printing out the tongue piece (I havn't progressed beyond this I'm afraid)the nozzle temperature drops throughout the print – instead of staying put at 205, it goes down into the 180's – I'm sure that this is one of the reasons that my prints are crap.



Any comments from people who know what is occuring?

I_max is a cap on the integral term on the PID controller. An overly large cap can result in oscillation, and overly small cap can result in the I term not being able to overcome the offset left by the P and D terms. If some of this doesn't make sense, google 'PID without a Phd' or otherwise educate yourself about PID. If you are using Marlin firmware, you can use the autotune function to get PID values that work pretty well. Send 'M302 SXXX' to start it, where XXX is an average working temperature.

As for your other problem, the usual cause is that the Gcode is requesting a lower temperature. Look for M104/M140 commands in the gcode and change their S codes to match the temperature you want. The better fix is to get your PID tuned properly.

Thx andrew

I looked at that post - then I morphed into homer simpson