Hot end temp swinging and bouncing

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Hot end temp swinging and bouncing

Postby Cre-ta Fab Lab » 2016-Nov-Mon-10-Nov

I'm experiencing an erratic behaviour in the hot end temperature reading.
As you can see in the image attached during the heat-up - when the temperature rise constantly - the reading seems just fine.
When the target temperature (210°c) is reached the temperature reading become very unstable and swings between 190°c and 220°c in a very short time ( couple of seconds ), this is preventing the firmware to start printing.
I don't think the real hot end temperature can phisically change so fast so I suppose is the temp sensor failing, anyway I tried with the process of recalibrating PID parameters but the behavior remains the same.
Anybody experienced the same problem before? Any idea what to try next?
Any help is kindly appreciated.
Screenshot 2016-11-21 10.38.28.png
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Hot end temp swinging and bouncing



Re: Hot end temp swinging and bouncing

Postby RetireeJay » 2016-Nov-Mon-21-Nov

How long have you had the printer? Did it behave well in the past and just suddenly start exhibiting this problem? Did you make any changes, like substituting an E3D hot end for the original Ubis?

Check for loose connections in the thermistor circuit and especially check for wires that may be exhibiting fatigue failure - meaning the copper wires inside the insulation are broken and making erratic contact. You check for this by manually pushing, pulling, and bending the wires, particularly at points where they get repeatedly bent back and forth in operation. You can do this with the hot end at room temperature; if the readout is unstable you'll be able to see it. (In the future, prevent fatigue failure with "cable chain;" search for it.)

Another possibility is that the PID loop needs to be retuned. This has been discussed several times; search for it.
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Printrbot Plus operational January 2013
Brass threaded rods (5/16" X 18) & nuts for Z axis
GT2 belts & pulleys
Cable chain to reduce probability of fatigue failure in wires
E3D V5 Hot End, 0.4mm nozzle, also 0.8 and 0.25 in use occasionally
PB fan mount + 40mm fan -- using printed mount adapter, not the E3D supplied fan
Injection molded extruder gears
Optical Z "endstop" (custom designed and built)
Have used many pounds of T-Glase filament. Now also doing some work with Ninjaflex SemiFlex
Print on glass with Scotch Craft Stick or other glue stick
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