Odd hotend pre-heating issue

I am having an odd issue with pre-heating the E3Dv6 hotend on my Prusa i3.

My setup is as follows:
Prusa i3
E3Dv6 hotend
RAMPS 1.4 w/ constant cooling to the board
Arduino MEGA 2560
Full Graphic Smart Controller LCD
12v power supply for the electronics
12v power supply for the bed.

Let me start this by saying that the machine has been working great up until now. Just starting last night, when I use the LCD or Pronterface to pre-heat the nozzle, it will get within 10 degrees of target temp and then slows down. It then gets to usually within 5 degrees and then settles back to 10 degrees below what I set it to. In other words, if I set it to 230, it settles to 220ish. If I set it to 240, its settles to 230.. I've tried 230, 240, 250, and 260 and I get the same result, a 10 degree decrease. I did a PID tune of the hotend and set those values in. I also tried uploading the firmware from my other i3 and it still does the same thing.

I have tested the main power supply and it reads 13v with no load and 12.4v with everything on and the nozzle set to temp.

I don't think its the hotend because it will heat fine minus the 10 degrees. Also, when printing, it will hold the requested temp just fine.

I'm thinking either the RAMPS board or the Arduino board?

Please, I really don't need answers like RAMPS is a bad board to begin with, you should switch to XYZ platform. It has been working fine for me for quite a while. As long as you work within its limitations, it is just fine. I'd just like to figure this situation out.

Edited 5 time(s). Last edit at 09/13/2015 04:29PM by SpeedyDad1.

It must be a cooling and pid issue as pwm kicks in 3 to 10 degrees before hitting the setpoint. If there's not enough power being fed or too much heat is drawn away the hotend will not reach the setpoint.

Is the fan cooling the heatbreak on at full speed? I've made a fan controller for mine and can barely hear it while still cooling really well. Is the heater block touching the cooler?

Make sure the pid values are being used. If you have the eeprom feature enabled you manually set the values using gcode, then save the settings to the eeprom.

See
pid autotuning

Edited 1 time(s). Last edit at 09/14/2015 06:13AM by imqqmi.

I played around with PID a bit to no avail. Then, I grabbed the heater cartridge from the E3D in the clone Ultimaker I'm building. I installed that in this heat block and tested it. It heated fine. I then swapped the old one back in and it also heated fine. I think it was either a loose connection at the RAMPS board or oxidation between the cartridge and the heater block.

What is your MAX_PWM set to in configuration.h (assuming you are using Marlin?). The E3D instructions say use 150, and for me that worked for a day or two and then (inexplicably) I found the temperature flatlining below where it should be, and PID autotune timing out. I raised it to 256 and all was good thereafter.

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See my blog at [moosteria.blogspot.com].

animoose - Looks like you hit the nail on the head. It started doing the 10 degrees below thing again so I upped the PID_MAX (couldn't find MAX_PWM) to 256 and it now heats up fine. Thanks!

Edited 1 time(s). Last edit at 10/03/2015 06:44PM by SpeedyDad1.

Quote
SpeedyDad1
animoose - Looks like you hit the nail on the head. It started doing the 10 degrees below thing again so I upped the PID_MAX (couldn't find MAX_PWM) to 256 and it now heats up fine. Thanks!

Great! And I did mean PID_MAX not MAX_PWM.

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See my blog at [moosteria.blogspot.com].