1 Topic by metaldrgn (edited by metaldrgn 2014-08-11 06:14:45)

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Topic: Erratic hot end temp

So since this last month I've noticed my hot end overcompensating from time to time to keep temps in the correct range. It's easier to explain by just looking at the pictures. The first 2 I was printing something, the third was just waiting for it to normalize before printing.  Prior to the third one I used the M303 S185 command to see if that would make a difference and it didn't. I didn't get a picture of it, but I've also had it where it would start out erratic, level out, then go erratic again towards the end. You can also see in all of the pictures (pictures 1 & 2 from the same time line) that the temperature spikes. In picture 3 it wasn't even printing, just idling with the fan on. I haven't tried using another material with a higher temp setting though to see if it holds true for higher temps.

Has anyone had issues like this? What do you think could be causing this? A few things I can think of are the heating element is failing or connections to it or the board is failing. I don't suspect the temp sensor.

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2 Reply by AZERATE

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Re: Erratic hot end temp

Did you recently make any changes to your printer or firmware?
I'm sure you probably have, but did you trace your wires and make sure they are connecting properly?

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3 Reply by metaldrgn (edited by metaldrgn 2014-08-10 17:56:27)

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Re: Erratic hot end temp

No changes were made.

yes I checked the wires to make sure the connects were good.  I haven't shot the wires/heater element, but that's next.  It's just weird because like I was saying, sometimes it levels off great on the start of a print, but then, mid print, it starts going erratic like you see in the pictures where it just won't stabilize.

One thing I should mention is the first time I noticed this I was printing with taulman 618 @210C and it spiked above 240C and smoked a little (It wasn't the nylon, maybe PLA since I had recently switched and there was some residual in there or PTFE, not good)! There was some delayed reporting while another command was in progress (homing I think) and when it showed the temp it was way too high.  The firmware disabled it after that because it exceeded the max temp, but none the less it overtemped. It would only do that on occasion after that and mainly only prior to starting a print and obviously it's gotten worse.

4 Reply by AZERATE

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Re: Erratic hot end temp

I think the thermistor is going bad.
It wouldn't be the heater because then it would struggle to heat in the first place. The thermistor is what reads and regulates the heat.

It may be possible that a wire for the thermistor has a slight break in the line to where it still gets electricity, loses the current as it moves and the wires bend while printing. Either way, I HIGHLY recommend not leaving your printer unattended whilst printing until you have the temp under control again. Please use caution.

Printit Mason and Printit Horizon printers
Multiple SD2s- Bulldog XL, E3D v5/v6/Lite6, Volcano, Hobb Goblin, Titan, .9 motor, Lawsy carriages, direct Y drive, fishing line...the list goes on
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5 Reply by metaldrgn (edited by metaldrgn 2014-08-10 18:35:38)

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Re: Erratic hot end temp

The main reason I don't think it's the temp sensor is that it spikes up, but not down if that makes sense.

Well, I guess it does a little.

I've also noticed weird things prior to any of this where the temp would continually rise up to the set temp, but the extruder output was 0 indicating it should be cooling off. Have you ever noticed that?  I don't have a picture of that either.

6 Reply by metaldrgn (edited by metaldrgn 2014-08-10 19:47:53)

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Re: Erratic hot end temp

Well I was playing around with some settings, took the fan off, and was about to try ABS@200 when this happened: (see attached picture)

Looks like you're right.  I moved the head from the home position to set the height for the glass I was using and I saw this after. It left a scorch mark on the paper I was using to check for level which is how I noticed it.  No smoking this time though, but it passed the 240C mark again and that's not good. I'm going to see if I can find the open. These printers should really be dual redundant just for this reason.

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7 Reply by metaldrgn (edited by metaldrgn 2014-08-11 05:26:28)

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Re: Erratic hot end temp

Thanks it was actually the connector wires for the temp sensor. I saw the temp drop by wiggling the connectors so i knew it was at that point. I soldered the wires to the pins on the thermistor side to start with and I couldn't get it to dip again so I'm printing now and it's way better. The way the connectors are pinned need to be done differently. They're just too fail prone.

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8 Reply by grob

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Re: Erratic hot end temp

If this has freaked you out at all, for the addition of a second thermistor and cabling, you can have redundancy. Marlin has the support for it - it reads two temperatures, and if they ever differ by more than a given amount it aborts.

On the solidoodle board you'll need to assign one of the expansion header channels to be the other thermistor, and put in your own 4.7kohm pullup, but I don't see it as un-do-able. RUMBAS and RAMPS should have enough thermistor I/O to do it in any case.

http://jheadnozzle.blogspot.com/2013/11 … rt-in.html

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9 Reply by metaldrgn

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Re: Erratic hot end temp

grob wrote:

If this has freaked you out at all, for the addition of a second thermistor and cabling, you can have redundancy. Marlin has the support for it - it reads two temperatures, and if they ever differ by more than a given amount it aborts.

On the solidoodle board you'll need to assign one of the expansion header channels to be the other thermistor, and put in your own 4.7kohm pullup, but I don't see it as un-do-able. RUMBAS and RAMPS should have enough thermistor I/O to do it in any case.

http://jheadnozzle.blogspot.com/2013/11 … rt-in.html

I just think it's not really safe if it can cause burning of the PTFE seals or something worse. As of now I just watch the temps for excessive fluctuations and I check on prints every so many hours depending on the print. I eventually want to install one of the E3D v6 hotends and will maybe attempt it then. The second thermistor could also help protect the extruder if the fan for the extruder died allowing it to get too hot.