Extruder stops heating after initial temp is reached.

[Miguel Salas]

Hello all, I have a problem with my Prusa Mendel I2. After the extruder and heat bed reach the desired temperatures it starts to print. Right after the print starts the extruder temperature will go down. This happens every time. Has anyone experienced the same problem and how can I fix it? I can provide more details if needed.

Thank you.

[Ken Snyder]

​Do you have it in a cold place like a garage and does the temperature drop when the hotend fan comes on?  If so, you might want to set the fan speed down to 50% in the G-code.​

On Fri, Jan 16, 2015 at 9:31 PM, Miguel Salas <mcl....@gmail.com> wrote:

Hello all, I have a problem with my Prusa Mendel I2. After the extruder and heat bed reach the desired temperatures it starts to print. Right after the print starts the extruder temperature will go down. This happens every time. Has anyone experienced the same problem and how can I fix it? I can provide more details if needed.

Thank you.

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[Miguel Salas]

No, I have in a corner on my bedroom that is away from windows. I have not installed a fan on the extruder. Thank you for the response

[Bill Seiler]

Bad connection on thermistor.  Check all your connectors.

On Jan 16, 2015 9:31 PM, "Miguel Salas" <mcl....@gmail.com> wrote:

Hello all, I have a problem with my Prusa Mendel I2. After the extruder and heat bed reach the desired temperatures it starts to print. Right after the print starts the extruder temperature will go down. This happens every time. Has anyone experienced the same problem and how can I fix it? I can provide more details if needed.

Thank you.

--

[John Asay]

More details could be useful.

What software do you use for slicing?  Printing?

Is this a new occurrence, has it always happened, or is this your first few tries at printing?

Does the temperature drop to a fixed value and then stabilize (e.g. from 230º to 220º)?  If so what temp? Or does it drop back to room temp?

Does the temperature drop happen immediately (before extruding), after the first layer, some random time after start?

Some things to consider.  

*Many (all?) slicing programs allow you to define the temp for the first layer and other layers separately.  This is independent of host program temperatures.  It could be that you are setting the temp manually in the host/printing program before starting the print but it is being redefined in the gcode at the start of the print (or start of a different layer) by the slicer program.  Check your slicer program for these settings or maybe search your gcode files for "M104" commands.

*Do you have any custom start or end gcode set to be inserted into gcode files by the slicer?  Could be a M104 command in there somewhere.

*If you manually heat the extruder and leave it that way does it maintain a steady temperature?  Bad PID settings can cause the temperature to fluctuate for quite awhile after reaching set temp.

*Was your I2 prebuilt, a kit, manually sourced?  Presumably you have enough power in your power supply for heaters, motors, etc.

I think there were a few other ideas rattling around in my head when I started typing, but I'm too tired to think.  I'll leave out cooling and connections since Ken and Bill already mentioned those.

John A.

On Fri, Jan 16, 2015 at 9:31 PM, Miguel Salas <mcl....@gmail.com> wrote:

Hello all, I have a problem with my Prusa Mendel I2. After the extruder and heat bed reach the desired temperatures it starts to print. Right after the print starts the extruder temperature will go down. This happens every time. Has anyone experienced the same problem and how can I fix it? I can provide more details if needed.

Thank you.

--

[Miguel Salas]

Checked the connections this morning and they are all good. Then, I thought about your logic. There had to be some sort of resistance somewhere. I checked the wires and indeed one of then was bent sharply. From what I understand this created resistance. I fixed it and now the printer is working properly again. Thank you very much for your help guys!!!!

[Matthew Andrews]

If unbending a wire really fixed the issue for you then it's likely that you have a wire with an internal break that's making an intermittent connection(possibly making/breaking the connection when the printer starts to move.) simply having a sharp bend in the wire without breaking the conductor should not cause a measurable change in resistance. If it were my machine I'd be worried about the intermittent connection being high enough resistance, and or arcing enough to be a fire hazard and would replace the wire. 

-Allie

[Bill Seiler]

Check your wires to the thermistor too.