Extruder temp undershoots, even in auto tune

breadandbudder

Hi, all. I was just finishing up a project for a family member when my hotend stopped working. I've tried searching for solutions, but keep seeing the same pages with no solutions. Any help would be greatly appreciated.

The problem:
Most of the way through an 11 hour print (ASA, 260°), I noticed the hotend temperature was fluctuating down about 4 degrees and back up over about 5 minutes and just kept doing that. I attempted to auto tune the heater using "M303 H1 P1 S280" and a range of lower temps and tried increasing the dead time to 30, but each attempt resulted in "Auto tune cancelled because target temperature was not reached" (see screenshot example). If I try to heat it outside of auto tune, the temp plateaus 5-10 degrees short of the target. I checked and the heater cartridge and thermistor are not loose.

target temperature not reached.png

My setup:
I have an E3D V6 30w (with silicone sock) connected to a Duet 2 Maestro running firmware version 3.2 and Duet Web Control 3.4.6. I extended the wires for both the heater and thermistor and it had been working for many hours of printing before this. The resistance is 21.3 ohm. I normally print ABS at 245 and only just started printing ASA at 260 for the last 30 hours of print time.

Side question: what is the default dead time/ what should I set that to?

droftarts

@breadandbudder Judging by that heater curve, there's something wrong with the heater or wiring. This is a trace from my E3D v6 hot end, with a 12V 30W heater cartridge, heating up to 280C as normal with the print cooling fan on (ie not autotune) so PID kicks in close to target:

This is a normal heat up, so PID kicks in close to 280C. Your heater should easily get to 300C. Check:

The heater resistance may be increasing as temperature increases.
There may be damage to the wiring
The wiring may be loose in the terminals or crimps (this will generate heat)

Check the wiring, and all connections. If they seem okay, it may just be a failing heater cartridge, which is pretty easy to replace.

Ian

breadandbudder

@droftarts The wiring was actually the next thing I was going to check. Did not know the resistance could change with temperature though.
Here's what I've done so far:
-Removed and reseated thermistor and heater cartridge in heater block.
-Cut and reseated heater wires in screw terminal. Auto-tune was working at 260 degrees, but not higher.
-No heat felt at screw terminal during testing.
-After a failed auto-tune while it was still hot, I measured the resistance and it was the same. Not sure if that was the right way to test that.
-Cut extension off of heater wires (21.2 ohms now vs 21.3 before). Same result from auto-tune. 260 works, but not higher.
-Switched from E0 to E1 terminal. Same thing.

At this point, I think I need to replace the heater. I'm looking at a E3D 24v 40w heater cartridge, but higher wattage ones are cheaper and more abundant on Amazon. I'm just not sure I feel comfortable with more power draw, though it seems my original Ender 3 PSU should be able to support it. Could I get a 50w or 60w cartridge and run it lower by setting the P value lower in the M303 command? Any suggestions on where to source a quality heater cartridge relatively quickly?

Phaedrux

@breadandbudder said in Extruder temp undershoots, even in auto tune:

Any suggestions on where to source a quality heater cartridge relatively quickly?

I would avoid Amazon. You really never know what you're getting. I don't know where you're located, but an official E3D reseller would be my choice.

engikeneer

@breadandbudder check you have assembled the hotend correctly with a decent clearance between the heater block and the heatsink. 9 times out of 10 when I've seen V6's that can't hit temperature it's because the heater block is clamped up tight against the heatsink.

If you're not sure, you can post an image of your hotend here.

Also agree that I'd only really trust the proper branded heater cartridges. I've played with cheaper ones in the past and they are generally smaller and less round so don't clamp as well in the block. I had one fall out during a print once, though will never be sure if that was poor quality part or poor quality assembler...
30w should be plenty for what you need, but a 40w would also be fine. Much above 50w on a v6 can get very hot if you get thermal runaway so I would avoid those unless you are using copper blocks etc to reach real high temperatures (400C plus)

breadandbudder

@droftarts, @Phaedrux, @engikeneer, thank you all for your replies. Turned out to be a faulty heater cartridge. I received a new heater cartridge from an official E3D reseller. It has the correct resistance and is working well.
I suspect the original 30w heater was faulty from the start. When I first got my V6 3 years ago, I think I was only ever able to tune to around 260 and now that I'm printing close to that, it wasn't stable while also pushing filament through.
Also, there is adequate space between the heatsink and heater block.
Glad to have my printer back. Thanks for the help!