Extruder thermistor problem

valiobg

I have a problem with extruder thermistor. It shows higher temperature than actual. When I heat to 100 degrees and it shows 100 in octoprint but real temperature is 80 C. Room temperature is correctly measured by the thermistor. I usually print with 205 C and when the problem occured, a cold extrusion has caused a blockage of the filament in the extruder. Now I cannot pull out the remaining filament. Is the thermistor defective ?

Samuel Pinches

Welcome @valiobg ,

The max temperature on the nozzle is 250C - can you try heat to 250C and try and remove the remaining filament?

Then, you can unplug the thermistor and measure the resistance using a multimeter. The resistance will vary with temperature:

25C = 100k

80C = 10.7k

If the resistance measurement is correct, then you need to check the wiring is intact, and not damaged. Poor connection will result in lower measured temperature.

Screen Shot 2019-04-15 at 1.15.11 am.png

valiobg

I will try that. I use your firmware (Marlin 1.1.9C Beta). Da Hai gave me an advice to do the steps as in this video - https://youtu.be/brl1weuD8bs
but isn't the problem with the lower actual temp in stock firmware fixed in your 1.1.9 version ?

Samuel Pinches

It should be fixed in 1.1.8C, and I'm pretty sure I included that in the 1.1.9 beta.... so I'm not sure what is going on for you. Perhaps try 1.1.8C and see if it makes any difference?

valiobg

I have two TMC2208 for X and Y in UART mode. They refuse two work with 1.1.8. I tried to heat to 250 real temp but filament still cannot be pulled out. It doesn't move at all. What can I do ?

Samuel Pinches

Can you push and extrude? Otherwise I think you're going to have to test the thermistors and find out where the problem is...

Samuel Pinches

If you touch the nozzle with scrap filament, does it melt?

valiobg

I set to extrude with a command from the LCD and push with pliers. But it doesn't move at all. There is some melted filament which leaks from the nozzle when I heat to temp over 200 C.

Samuel Pinches

Maybe there is a jam in the PTFE tubing? I think you may need to disassemble the hot end, because this does not sound like a heating problem.

valiobg

Yes, you are right. The temp readings from the thermistor are correct. I measured the temp with another thermometer. There is a jam in the PTFE tubing probably. I have a video how to disassemble the hot end from the USB Flash stick that came with the printer. Thanks for your help.

Samuel Pinches

No worries.. good luck!

valiobg

Today I found where is the problem. The filament has melted in the extruder gear. The motor reaches 52 degrees when working. It has a TMC 2208 in Spreadcycle mode programed via OTP mode. Will I have do decrease the current of the motor ? Now it is 1.32 Vref. Initially it was 1.1 V but the motor was skipping steps.

Enrique Riri

My solution. I updated all my 3 printers like that using TMC2208 and no more worries

Der_Muck

I only can say, everything over 1V is to much for those stepper motors. Not one motor of my JG is over 0,8V and with that, they will stay warm.  Before my extruder motor was untouchable after 20min printing.
I also add cooling ducts on the extruder but it was for nuts because with 0,750 the extruder motor will get little warm. 
Maybe its a problem of the TMC2208 that it skips steps and so you need higher V but thats not optimal at all.
P.S. 1,32 is much to high
You can also check your Y motor, mostly that motor is constantly to hot wile printing.

Samuel Pinches

To reduce the extruder motor force required, you can shorten the bowden tube length (it is excessively long) and you can add some canola oil to tube to help lubricate the filament.

Der_Muck

Or higher the print temperature, to low temps. equal in a higher extruder motor force to. I had that problem with TPU but it equals more in filament slipping.

ufodoctor3

Replacement of the temperature sensor at the extruder
Hello Forum
If you need to exchange the NTC temperature sensor of the extruder, I found out
by measurements at the JGaurora5 electronics/display and consulting the data sheets,
that the Digi-Key Sensor 495-2125-ND (B57540G0104F000 from EPCOS) is compatible with
the original JGaurora sensor for about 5$ only!
Good luck
Peter

valiobg

I successfully fixed the problem. Now temp of motor is 31 C. Was 52 C.

valiobg

I bought canola oil for the filament also. But is it possible to have problems with first layer adhesion to bed if I use canola oil for the PTFE tube ?

Samuel Pinches

 As long as you’re not deep frying your printer, I think you should be fine with a drop or two. I haven’t had any adhesion problems since adding oil.

Der_Muck

I add PTFE oil and didnt had problems to, it only sounds strange to use oil but it works for PLA

I would change that motor to a better one, I also had such an bad motor, always a bit warm and at the end skipping steps while fast retracts. The JG stepper motors are not very strong. There are stronger once which work perfect.

1.5A 17HS4401S 1.8° with 0,42Nm

valiobg

Der_Muck, I have two of this motors - 

ZONESTAR Step Motor SL42STH40-1684MA-16 Torque: 4000g.cm Current:1.7A 1.8 degree

left from my Tronxy P802M. Are they suitable for the extruder of A5 ?

Samuel Pinches

They are rated for a higher power (1.7A) so they should be perfect  

Der_Muck

@valiobg
Yeah, they are even little stronger  
I can say that this motor shouldnt get to warm with the standard extruder. Set the current only so high that it doesnt skip steps. That should let the motor colder and gives the motor a long live time. Between 450-650 would be ideal. Over 750 the motor will always get very warm. 900-1000 is always to hot. That is how it behaves on my printer.
On the Y axes, they would also be great
And one last tip, if you have a TMC on the extruder, turn the strealthchop off. It causes missing steps on the extruder in a way, you doesnt see it, happened to me, took me a long time to find that out. So in that way, you can even speed the extruder motor up without a problem.