E3D-V6 Lite: Thermal Runaway

Discussion in 'E3D-v6 and Lite6' started by Apathy, Aug 2, 2017.

  1. Apathy

    Apathy Member

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    I've been using the V6-Lite for about 6 months and it's been performing for me without a problem up until now. Unfortunately I can't finish a print, the temperature of the hot-end stays steady for ages then all of a sudden it starts to oscillate below the set temperature by about 5 degrees and the set temperature, causing the thermal runaway protection to kick in on the marlin firmware. I've attached a screenshot of the temperature plot after failure.

    I've tried using the PID auto-tune but still having the same problem. I have it sat on the bench at the moment reading about 107KOhm at room temperature. The connections to the plug that came on the thermistor cartridge aren't damaged and appear to be fine on visual inspection. I tried wiggling the cables during operation and didn't observe any errors on the temperature readouts.

    Hope you can help!
    Thanks
     

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  2. Antoine

    Antoine Well-Known Member
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    Does this happen when your part cooling fan kicks in (layer 2/3 depending on your slicer settings). Sometime the additional cooling provided by the air flowing over the heater block can be sufficient to unsettle the PID. If this is the case, either run the PID tuning with the fan on, re-design your part cooling duct to avoid cooling the block, or put a silicon sock on it.
    Another possible cause would be a heater cartridge which doesn't have enough power to heat the block up when the part cooling fan is on. This can happen to old heater cartridges, which can degrade over time.
    You might also have a loose connection in your heater cable which stops the heater from heating properly, check your heater wiring. This doesn't seem like a sensor issue, more like a heater/cooling issue.
     
  3. Old_Tafr

    Old_Tafr Well-Known Member

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    PID can also be upset, so give the wrong readings if there is a draft (like an open window) when you do it. Mine failed like this, but was fine when I re-ran it. And the numbers were quite different.

    Did you change the layer level at which the fans come on ?

    Lots of problems are solved by the "what did you do last?" however innocuous the last thing was.

    If it isn't that then either some environment thing changed or something actually broke.
     
  4. Old_Tafr

    Old_Tafr Well-Known Member

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    Loose wires sounds good, and maybe the problem gets worse especially if the fault is internal to the heater, when it has been hot for a while..

    Another possibility is the mechanical contact between the heater and the heat block. Maybe the Al block expands more than the heater cartridge itself = poor contact = slightly less heat transfer = temp drop = thermal runaway. Which could be made worse by a heater cartridge on its way out.

    107 K ohm does not sound right, I have a spare, no idea if it is 12v or 24v but it reads 22 ohms. (no "K" involved)

    OK read the lable, it's 0 to 24v 30 watts.

    If yours measures in "k" ohms then it is almost open circuit. Assuming 24v then watts = V (squared) / R = 0.005 watts

    Also the thermistor is the temp measuring device (resistance changes with temp) as it's not clear if you are talking about the heater cartridge (which would be a good idea to measure) or the thermistor. I guess from the above calc you are talking about the resistance of the thermistor.

    Try checking the mechanical fit of the heater and the resistance of the heater.

    PS Measured a spare thermistor, after capacitive effect about 103 k ohm.
     
    #4 Old_Tafr, Aug 2, 2017
    Last edited: Aug 2, 2017
  5. Apathy

    Apathy Member

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    No it's after about and hour or so of printing (The hotend drops temp by about 5 degrees on the fan start up but it does recover after a few seconds) I thought it might be the part cooling fan so I dropped that to 50% but that didn't change anything. I never considered the heater cartridge. After checking the wiring that all appears to be OK so perhaps it's just at the end of its life span.

    Thanks for the comment
     
  6. Apathy

    Apathy Member

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    Sorry for not being more clear, I was referring to the resistance of the Thermistor Cartridge which is a 100K Semitec 104GT2 NTC thermistor. I'll have a look at the tolerance between the cartridge and the aluminium block although I would be surprised if that was it. My heater cartridge is a 12V 25W. I only really print PLA and PETG, occasionally TPU and it has been working perfectly up until now.

    Responding to your other comment, I keep my printer in a home built enclosure and don't have any draft issues. Literally the only thing that has changed between the printer functioning as expected and not functioning as expected is time. One day it was fine, the next it was not. Part of the hobby I guess :)

    I'm starting to think the heater cartridge is giving up on me.

    Thanks for your comment
     
  7. Old_Tafr

    Old_Tafr Well-Known Member

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    Interesting that your heater cart is 25w and the spare I have is 30w as I do remember comments saying that there were situations where there wasn't sufficient heat. I have only used PLA and ABS as yet (waiting on a response from E3D about some Edge filament only available in 1.75, other colours only in 3mm as I don't really want to change the complete extruder from the original 1.75)

    Maybe a boot on the heater block would help short term and/or if you still use 25w and not 30w.
     
  8. Apathy

    Apathy Member

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    UPDATE: I'm currently 2 hours into a PLA print and it's going fairly well for the most part (100% cooling fan), watching the temperature plot like a hawk. It's a little irregular (see picture) but it's working for now. I'll order a new heater cartridge and while I'm at it I may as well get another thermistor cartridge too just for good measure. Will continue to update with results at a later point.
     

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  9. Peter Mather

    Peter Mather Member

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    Are you using Ramps PCB? Could also be the resettable fuse dropping out with overheat and then resetting particularly if you are in a hot enclosure
     

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