Erratic Hot-end Temperatures

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Caelum
Posts: 5
Joined: Tue Feb 25, 2014 5:28 am

Erratic Hot-end Temperatures

Post by Caelum »

Hi All,

Have this week received my Felix 3.0 kit, and assembled over about 3 nights. Got it working yesterday, and after a short calibration, was smashing out prints in awesome quality.

Having successfully printed several items (in fantastic quality) i thought i'd set up/calibrate the second extruder, and run through some ABS. After a few teething issues, i've just now completed the 40x10 print onto kapton at 245 degrees(on the high side, i know), with a bed temp of 80... Success! Or so i thought....

Went through to test another PLA print with my usual settings (200 for the hot end, 55 for the bed), and had the print fail. Totally. No adhesion with the print bed, filament not feeding properly, total mess...

Then i noticed the temperatures for the first extruder were fluctuating wildly... So much so that i couldn't reliably determine what the extruder temp actually was... But i'm sure it was hot, as PLA was oozing from the nozzle without me pushing any more filament into it... so probably 230+.
Screen Shot 2014-03-23 at 10.03.11 pm.png
Checked the wires, everything seems ok... power cycled the control board, didn't help. Thought i'd take the sledge-hammer approach and reflash the arduino completely... No help. You can see it gets up to about 150 degrees without too many fluctuations, but then it goes off the scale again...
Screen Shot 2014-03-23 at 10.14.01 pm.png
Thought i'd double check the second extruder, to make sure it wasn't a general system error, however the second extruder that i used for the ABS print earlier, is looking fine...

Anyone have any thoughts or suggestions to nut out this problem?

Cheers,

Cae.

andrewsi
Posts: 130
Joined: Mon Dec 23, 2013 1:26 am

Post by andrewsi »

If you swap thermistors with the other extruder, does the problem follow the thermistor? If there's enough slack, they can be moved easily after loosening the set screw on the bottom of the extruder head.
__________________________________________
Andy Silverman, Technogeek in Seattle
Felix Tec4 Single-head

felix GH
Posts: 6
Joined: Sat Nov 09, 2013 4:44 pm

Post by felix GH »

I had the same thing happening at work, we have a Felix 3.0 single head the temperature was going crazy, finally after touching the Thermistor cable it went blank 0.0C, this was happening running the PLA at 215C large print. We changed the Thermistor which came as spare and it was good until I ran the temperature at 215C again. Talked to our electronic people, they suspected that the Thermistors were only rated for 200C or the adhesive used to attach the Thermistor into the housing was the wrong one and expanded resulting in damage.
At home I have a Felix 2.0 never had any problems, but I noticed the Thermistor is secured with high temp RTV not like the others with some sort of hard epoxy.

I ended up lending my spare from the Felix2.0 to work and trying to find replacement Thermistor rated
for 300C (100K at 25C). This is not that easy I will have to place the Thermistor into a housing and insulate the legs with some Teflon tubing as none I could find came assembled like the Felix once.

andrewsi
Posts: 130
Joined: Mon Dec 23, 2013 1:26 am

Post by andrewsi »

I've encountered exactly the same thing - my first 3.0 thermistor went erratic and was no longer reliable (although I never used it much above 195), and I had to replace it with the spare. I too think that the hard material used to seal the thermistor into the metal casing isn't permitting any thermal expansion and perhaps causing damage.

I tried to drill out the stuff inside the case of the bad one so I could reuse it with a new thermistor, but even with a Dremel I had no luck at all, it's really tough stuff and folks here suggested some pretty nasty chemicals that I don't think I can find easily. Instead, I decided to take this route: First, I ordered some new EPCOS thermistors rated at 300 from Mouser (in the USA there are several good components distributors to choose from). I alsoi found a hobby store nearby that sells brass tubing in just the right size (3mm x .225mm thick walls) for just a couple bucks (the company that makes it is www.ksmetals.com), so I think when I need to finally do it, I can cut a short length of that, insulate the thermistor leads with heatshrink tubing, then stick it in and seal it in with high-temp RTV, and use that as my homebrew replacement for the Felix ones. We'll see how long the "genuine" spare lasts first, though.
__________________________________________
Andy Silverman, Technogeek in Seattle
Felix Tec4 Single-head

Caelum
Posts: 5
Joined: Tue Feb 25, 2014 5:28 am

Post by Caelum »

Nailed it, thanks guys... Swapped out the thermistor with the spare that came in my kit, happily printing again... for now!

Legion 2.3
Posts: 84
Joined: Sun Apr 20, 2014 6:23 pm

Post by Legion 2.3 »

My temps are also a bit jumpy, but not as extreme as Caelum´s.
Temp_2.JPG
What do you say, is it still normal or a sign of a failing thermistor?

andrewsi
Posts: 130
Joined: Mon Dec 23, 2013 1:26 am

Post by andrewsi »

I'll bet high odds that what you have is indeed a failing thermistor. I just had my second Felix-provided one fail with the exact same symptoms as you, and as the first one I had that croaked. Over a period of a few days worth of printing, jumpy spikes in the temp graph like yours started appearing, growing worse and worse over time. I just now replaced the bad one with the homebrewed one I described above, using the 3mm brass tubing and high-temp RTV, and a genuine high-temp EPCOS thermistor, and the temp readings have gone back to rock solid... we'll see how long this one lasts. With any luck, it'll do better than the 2.5 months each of the Felix thermistors survived before getting too erratic to use. Hopefully the RTV will be the cure, that super-hard epoxy in the Felix thermistor cans definitely seems suspicious from a thermal expansion point of view.
__________________________________________
Andy Silverman, Technogeek in Seattle
Felix Tec4 Single-head

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