Autotuned Extruder Consistently Under Temp

atomictangerine39

Hi! I’ve bought various parts for a homemade 3D printer, and I’m running into a problem with either the PID tuning, the extruder, or motherboard. When I autotune the PID in Repetier-Host (using m303 e0 s###) and upload the updated values using repetier-firmware on arduino, the actual temperature is consistently 2-3°C under the target temperature. This has happened when I tuned it to 240°, 235°, and 230°C.

I am using a Melzi v2.0 board from an old Tronxy X1 (with custom repetier firmware) with a MOSFET for the extruder, but before I had the MOSFET the same problem was occurring.

I’m using the MkIII extruder, or whatever extruder the Anet A8 uses if I got the model name wrong.

Is this an issue that can be fixed with manual PID tuning (which I have sort of tried), switching to bang bang, or do I have to get a new motherboard, or what?

Repetier

Such things can happen. Have had it my self as well. Auto tune is just a heuristic approach as you already see with the many possible equations to select from. It can also get worse if the temperature readings are not smooth - also we already smooth them internally. Make sure max pid is 255 and that you do not constrain I gain too much:

/** \brief The maximum value, I-gain can contribute to the output.

A good value is slightly higher then the output needed for your temperature.

Values for starts:

130 => PLA for temperatures from 170-180 deg C

180 => ABS for temperatures around 240 deg C

The precise values may differ for different nozzle/resistor combination.

Overridden if EEPROM activated.

*/

#define EXT0_PID_INTEGRAL_DRIVE_MAX 205

when that is lower then what you need for your temperature you will get exactly your effect as well. Should be editable in eeprom so just check what it is set and increase it and see if it improves.