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Anyone else notice part fans cause hotend thermistor to falsely report cool bed?

Discussion in 'Troubleshooting' started by supercazzola, Jan 28, 2018.

  1. supercazzola

    supercazzola Active Member

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    On my R2 with the improved parts fan shroud, I noticed that the print temperature of the hot end could never exceed 205° when the parts cooling fans were turned on at 100%.
    I know you’re asking why would I want to have the fans on if I had to print material like ABS or PETG which require higher temperatures and desire no cooling, but it bothered me that the thermistor was reporting a false temperature due to the fans blowing across the exposed metal sleeve of the thermistor. I began to think that perhaps with the fans on, there would be a difference between actual temperature of the hot end and what the thermistor thought was the temperature even printing PLA.

    So I began a series of tests…

    Below is my temporary solution until Robo changes the way the thermistor fits into the heater block of the hot end.

    First, I obtained a silicone cover for the hot end. Mine happened to be black.


    Next, I had to punch some holes through the bottom to allow for the set screws to be accessed.

    And just for good measure, I used high temperature silicone gasket maker to seal off any potential contact between the area where the thermistor meets the heater block and air. The one I got was Red RTV, made by Permatex.

    I’m going to test this out, but so far it appears there is no chance that the air from the parts cooling fans will ever touch the exposed metal tube that the thermistor sits in. And that should mean accurate readings from the thermistor, and true temps for the hotend.

    [​IMG]

    [​IMG]



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  2. WheresWaldo

    WheresWaldo Volunteer ( ͠° ͟ʖ ͡°)
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    Get a silicone sock and that will help retain the heat generated
     
  3. supercazzola

    supercazzola Active Member

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    Is that different than the cover I used ?



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  4. WheresWaldo

    WheresWaldo Volunteer ( ͠° ͟ʖ ͡°)
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  5. supercazzola

    supercazzola Active Member

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  6. WheresWaldo

    WheresWaldo Volunteer ( ͠° ͟ʖ ͡°)
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    Oops missed that ;tldr
    I have not had that issue, are you using the default firmware?
     
  7. supercazzola

    supercazzola Active Member

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    No, beta...
     
  8. Redriche

    Redriche Member

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    I've printed and use the new fan shroud Robo released that's on thingieverse and I have not experienced this at all. I have been printing one PETG as I'm getting ready for my MK3 and building a lack enclosure, so no fan usage lately, but even before this I've had no issues.


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  9. supercazzola

    supercazzola Active Member

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    To test it, it is counter intuitive (because you would probably never cool the part when your extrusion temp is so high). Set you hotend to 245. Then raise the bed up so that it is close to where it would be at start of a print. Then set the parts cooling fans to 100 % and see if the unit maintains the temp, or if it times out after temp drops


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  10. WheresWaldo

    WheresWaldo Volunteer ( ͠° ͟ʖ ͡°)
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  11. supercazzola

    supercazzola Active Member

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    My brain see this as a different problem. If the fan is truly impacting the thermistor, it happens at all levels (unless you think that by the bed being farther away from the fans, less air is bounced back up at the thermistor.

    What I was thinking was that even for parts printed with PLA, if the parts cooling fan is needed, the airflow is impacting he thermistor. That is a bad thing. If the hot end is changing, and the thermistor picks it up, then that is okay, but if the thermistor metal container sticks out too far from the heater block (it is on my 3 hot ends) then if the thermistor wasn’t positioned well in that metal tube, then maybe it is picking up the temp of the metal tube and not the heater block. That is what I was trying to state and test by my experiment - not whether or not a smart 3D printing person would ever do that.

    Make sense?






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  12. mark tomlinson

    mark tomlinson ༼ つ ◕_ ◕ ༽つ
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    This is a problem that really needn't be. When all the hotends had 40w cores this was not generally an issue :)
    I still only use 40w cores (even in the hexagons). If that has issues with maintaining temperature ... it is a bad core.
     
  13. WheresWaldo

    WheresWaldo Volunteer ( ͠° ͟ʖ ͡°)
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    What your saying makes sense, but....

    1. Try PID tuning.
    2. If you parts fans should be directing air toward the part and not the hot zone of the hotend. If it is blowing air on the hot zone it is a poor shroud design.
     
  14. supercazzola

    supercazzola Active Member

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    But is it a heater issue or a bad sensor that tells the control process I need more heat? My concern is it is causing the heater to get too hot. A heater is only as good as the tool used to measure it. And a $1 part from China is what this is relying on.


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  15. supercazzola

    supercazzola Active Member

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    That is what I’m trying to determine, and to bring back to Robo’s attention


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  16. WheresWaldo

    WheresWaldo Volunteer ( ͠° ͟ʖ ͡°)
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    Unfortunately in my previous career I would just tell you that your results are an anomaly. There is little for Robo to do as the sample size is too small, at least as reported by forum posters. They can make note of it and then do what they do best and ignore it. So far I have seen no other reports here but yours. Since both heater cores and thermistors are cheap and PID tuning is free, you have options to test. There is no way for any of us to support or refute your findings.
     
  17. supercazzola

    supercazzola Active Member

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    Ok thank you


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  18. Geof

    Geof Volunteer Moderator
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    Both the C2 and R2 I'm running the V3 (thingiverse) fan duct and so far have not noticed an issue? I've had temps at 240 with fans on 30% and not seen the heater get over run by the fans? Like @WheresWaldo mentioned I'd start with a PID tune. Thats likely your best bet, but I'm also pretty confident its the "lack luster" electronic components in the hexagon (like you mentioned).

    for funsies:

    Running production work I tend to fix as little as possible. If its something that never happens when I'm printing materials, only a hypothetical like layer 1 100% fans with heater at 240....well....no material wants or needs that so I'd never see it. I have a stock R2 with that fan shroud and would be more than happy to see if I can reproduce it if your curious, but I see no actual issue as no material needs or should have cooling on the first layer or 2 (minimum) :D
     
  19. mark tomlinson

    mark tomlinson ༼ つ ◕_ ◕ ༽つ
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    Just my two pennies, but ... when the thermistor goes bad (the part that senses the temperature) it is a lot more obvious than just reading a bit off. If you had replaced the thermistor with a different type than the firmware expected ... it could and would read "off" but that is the only way
     
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  20. supercazzola

    supercazzola Active Member

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    Nope, stock thermistor


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