Hotend temperature fluctuations
May 16, 2019 04:01AM
I've been struggling with temperature issues on my hotend for seemingly months now. While the bed temperature has always been rock solid, the hotend can either be very solid, or just wildly all over the place, sometimes triggering a thermal shutdown. I'm running an i3 variant with Ramps 1.4, Arduino Mega 2560 R3, and Marlin bugfix-2.0.0.

I'm running an E3Dv6 hotend that uses the thermistor cartridge. I'm connecting the thermistor to the Ramps board with the E3D supplied cable made for the thermistor cartridge. I've done the PID AutoTune.

What I'm seeing now, is terrible instability in the hotend temp at the beginning of the print, which smooths out later and either maintains through the rest of the print, or goes through other periods of instability. For instance, this is a print I attempted tonight. The first image is showing the last part of the first layer and going into the 2nd layer. This is not even the worst of the hotend fluctuations that occurred previous to what's in the image. You can see the bed switching from the first layer temp to the 2nd layer.


This image is at about layer 8. Temp levels out and remains very stable for some time. The third image shows this stable period.




Then around layer 20, the temp took about a 15-20 degree down spike and while it was climbing back up and I was going to grab a screen shot, it must have jumped the other way and triggered a thermal shutdown.

Hardware wise, I've swapped out just about every possible culprit. I have another E3Dv6 for another printer I'm building, so I swapped out the themistor cartridge with no change. I've gone through 3 sets of Mega/Ramps boards, no joy.

I've seen bugs in Marlin before that were causing some temperature issues, but those were fixed long ago and I see no open issues with Marlin currently. I just updated to the latest pull last night.

Could it be a power supply issue? The only thing I can think, if swapping the thermistor didn't cause any change is that something is causing fluctuation on the AREF which is then causing fluctuations on the readings. But I wish I knew why it always is just the hotend and not the bed. Seems like if it was a power supply thing, the bed would also be showing instability at the same time, but it doesn't.

Does anyone have any other ideas?
Re: Hotend temperature fluctuations
May 16, 2019 05:24AM
Just going out on a limb here and suggest that it might be a faulty MOSFET? Or maybe a break in the solder of the MOSFET?

Check the soldering of the MOSFET and see if it came loose somewhere. I don't know how you can check if a MOSFET has gone bad, but that's where I would check. Maybe just replace the thing since it's a cheap component anyway.

If it was a PSU issue, you would first notice this on the heated bed since that one pulls way more Amps. However, fluctuation on a heated bed is less noticeable since it has a larger thermal mass. But I suspect the MOSFET.


http://www.marinusdebeer.nl/
Re: Hotend temperature fluctuations
May 16, 2019 05:35AM
Quote
Ohmarinus
Just going out on a limb here and suggest that it might be a faulty MOSFET? Or maybe a break in the solder of the MOSFET?

Check the soldering of the MOSFET and see if it came loose somewhere. I don't know how you can check if a MOSFET has gone bad, but that's where I would check. Maybe just replace the thing since it's a cheap component anyway.

If it was a PSU issue, you would first notice this on the heated bed since that one pulls way more Amps. However, fluctuation on a heated bed is less noticeable since it has a larger thermal mass. But I suspect the MOSFET.

Hi Ohmarinus,

You mean the MOSFET on the Ramps board? Like I said before, I've actually tried three different Mega and Ramps boards in the effort to figure it out. My bed is a 12v silicon heater which I forgot has it's own control board and MOSFET which could be why I don't see any fluctuation there, but since I've tried different Ramps boards with no change, I'm guessing it's not related to that.
Re: Hotend temperature fluctuations
May 16, 2019 08:31AM
Quote
brucehvn
Quote
Ohmarinus
Just going out on a limb here and suggest that it might be a faulty MOSFET? Or maybe a break in the solder of the MOSFET?

Check the soldering of the MOSFET and see if it came loose somewhere. I don't know how you can check if a MOSFET has gone bad, but that's where I would check. Maybe just replace the thing since it's a cheap component anyway.

If it was a PSU issue, you would first notice this on the heated bed since that one pulls way more Amps. However, fluctuation on a heated bed is less noticeable since it has a larger thermal mass. But I suspect the MOSFET.

Hi Ohmarinus,

You mean the MOSFET on the Ramps board? Like I said before, I've actually tried three different Mega and Ramps boards in the effort to figure it out. My bed is a 12v silicon heater which I forgot has it's own control board and MOSFET which could be why I don't see any fluctuation there, but since I've tried different Ramps boards with no change, I'm guessing it's not related to that.

Ohhh I'm sorry, I missed that part! Then forget what I wrote. Just to be sure on the hardware side, did you replace the complete thermistor wire or only the cartridge?

Otherwise, I wouldn't have a clue about a current issue with Marlin..


http://www.marinusdebeer.nl/
Re: Hotend temperature fluctuations
May 16, 2019 09:56AM
Sudden erratic jumps in temperature readings are usually caused by bad connections to the thermistor, or a thermistor wire touching the hot end metalwork coupled with leakage in the heater cartridge. Just possibly by a faulty thermistor.



Large delta printer [miscsolutions.wordpress.com], Robotdigg SCARA printer, Crane Quad and Ormerod

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].
Re: Hotend temperature fluctuations
May 16, 2019 03:31PM
One other possibility is overloading the 5A polyfuse - if you have a lot of power to your steppers and the hotend, the polyfuse might start restricting the current and that could cause the hotend to fluctuate. Adding an external MOSFET for the hotend will solve that issue.
Re: Hotend temperature fluctuations
May 16, 2019 08:06PM
Quote
dc42
Sudden erratic jumps in temperature readings are usually caused by bad connections to the thermistor, or a thermistor wire touching the hot end metalwork coupled with leakage in the heater cartridge. Just possibly by a faulty thermistor.

Hi dc42,

That was my first thought, but I've got two thermistor cartridges and they show the same behavior. Unless I got two bad ones from E3D, it appears to be something else. The heater block has a silicon sock and I've made sure the wires are not trapped underneath or rubbing against anything hot. The wires pretty much come straight out away from the heater block. I'm swapping out the thermistor cable and trying one last mega board today and we'll see how that goes.
Re: Hotend temperature fluctuations
May 17, 2019 04:51AM
Quote
brucehvn
Quote
dc42
Sudden erratic jumps in temperature readings are usually caused by bad connections to the thermistor, or a thermistor wire touching the hot end metalwork coupled with leakage in the heater cartridge. Just possibly by a faulty thermistor.

Hi dc42,

That was my first thought, but I've got two thermistor cartridges and they show the same behavior. Unless I got two bad ones from E3D, it appears to be something else. The heater block has a silicon sock and I've made sure the wires are not trapped underneath or rubbing against anything hot. The wires pretty much come straight out away from the heater block. I'm swapping out the thermistor cable and trying one last mega board today and we'll see how that goes.

I expect swapping the cable will fix it. Let us know!


http://www.marinusdebeer.nl/
Re: Hotend temperature fluctuations
May 17, 2019 07:41AM
I have the same issue, almost exactly the same.

Bed temperature is rock solid, but hotend varies between stable and a bit wild. Can sometimes throw THERMAL RUNAWAY errors. I've upped the time period and temp variation allowances in configuration_adv.h in the hope that will help prevent failed prints.

I've also changed RAMPS boards, I'm using a new 1.4 board, with a 1.5 and a 1.6 to try also. I've also ordered a new thermistor cartridge from E3D (I'm running a genuine E3Dv6) so and will take extra care to make sure the thermistor cables are not unduly bent or touching the heater block, essentially I'll make sure the wires are in perfect order as they reach the RAMPS board.

Following this thread with interest!

Joe


JK3D Blog - [jk3d.wordpress.com]
Re: Hotend temperature fluctuations
May 17, 2019 09:24AM
Well, I was going to hold off on replying until I did another print later today, but last night I did 2 prints for a total of about 3 hours and didn't see a bit of instability in the hotend temperature. I changed two things, the mega board and the thermistor cable. Now I have to see which one was actually the problem. It should be pretty easy because the old thermistor cable is still there, I just ran the new one temporarily, so I can swap it back easily. The cables I'm using are the ones that came with the E3Dv6's. If it turns out to be the cable, then I guess I just got a bad one. I hope I'm not speaking too soon, but I will update after the next print, which will take about 2 1/2 hours once I start it.
Re: Hotend temperature fluctuations
May 18, 2019 01:38PM
Yep, mine was the thermistor (or most likely the cable from the thermistor that goes past the hotend). Changed it yesterday and temps are solid now. Glad it's fixed. I made sure to give the hotend a wide berth in terms of cable tidying.


JK3D Blog - [jk3d.wordpress.com]
Re: Hotend temperature fluctuations
May 19, 2019 05:13AM
I made my other print which was 2 1/2 hours with the old thermistor cable and didn't see any issues. I'm not ready to declare total victory yet, as I've seen cases where it could work for a print occasionally, so I'm going to print a few more to be sure.
Sorry, only registered users may post in this forum.

Click here to login