Extruder temp decreasing then decoupled during long print

Comments

• Repetier

  December 2016

  As long as head is moving it is not the power supply.

  
  

  First you should print with host and watch temperature graph and heater output. The big question is when any why the temperature is decreasing. Control will be still the same so when it gets colder it will try to heat. So from your description you should see target temperature stay high while temp falls and heater still fires. 

  
  

  At that stage 2 things might happen. 

  1. A fan was enabled cooling more then you can heat. Have seen users having that problem several times if the filament cooling wa salso cooling the extruder.

  2. No power to heater element. Some soldering that looses contact, MOSFET turning off from overheating, defect heater element.

  
  

  If you have a multimeter and access to fet outputs you could measure voltage when it happens. Helps to see on which side of the connector the problem is.
• pefozzy

  December 2016

  Thanks for the help. I checked the output voltage of the hot end, and it was fine. I took a look at the fan shroud and it seemed to direct most of it's output on to the hot end nozzle- so I redesigned it to direct more flow downwards. This seemed to do the trick, I've printed several big objects since then and it's worked perfectly. 

  
  

  I'm guessing when the hot end was close to the bed the cooling fan was pulling in warm air from the zone immediately above the heated bed. Once the object was tall enough- roughly 75mm - the print would fail almost every time. I found it interesting that the print failed at almost exactly the same height every time- seemed to be repeatable within 5mm of height. The zone of heated air above the bed must be very repeatable across multiple prints, and I don't have any sort of enclosure on my printer.