Another thermistor bites the dust

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killejano
Posts: 92
Joined: Mon Apr 01, 2013 7:23 pm

Another thermistor bites the dust

Post by killejano »

I left my printer to print last night. Long print with abs @ 230 degrees.

It must have given the wrong reading for some time berore failing because the hot end had gone so hot it has burned abs all over and the whole extruder carriage drooped. It's all a huge mess :? The termistors seem to be a real problem

Luckily i do have printed spares for the carriage and new thermistors from farnell arrived today. The thing i wanted to ask you guys is how have you connected these thermistors. What did you use to insulate the two wires and did you solder wires at some point? Can heat shrink take the heat or should I use heat rsistant silicone for the first like 5mm and solder with non lead solder after that or is it still too close?

Hugues
Posts: 270
Joined: Thu Apr 04, 2013 5:36 pm

Post by Hugues »

subscribed !
i should receive ABS this week and a spare thermistor,
so definitely interested to learn how to do this.
Hugues
Regards from Switzerland

rad
Posts: 36
Joined: Thu Apr 18, 2013 7:33 pm

Post by rad »

I don't know how others did it but I can tell you how I have done it.

There is a picture over there in the Arnitel Thread:
http://www.felixprinters.com/forum/view ... 8&start=20
(it's my old experimental extruder so it doesn't looks so nice anymore but I don't care it has to work)

I spread the contact just a little bit to have some more space between the wires for silicon and simpler soldering.
Don't spread too much that it doesn't touches the walls of the hole also when the sensors will move a bit through external force.

Cut the legs that they stand out of the hole say 10mm if the Sensor is inserted till to the bottom of the hole.
This should prevent that all the heat get's to the soldering of the wires that will be done at the end of those legs when running the printer.

I put the sensor first into a pill of thermal silicon till it was nicely and equal covered and then I inserted it into the hole as far down as possible. Move it out and in a bit to make sure you leave no bubbles in there. Then I filled the hole with silicon and again made sure I left no air bubbles.
The I placed the extruder at a wall with the sensor sticking vertical out and nicely centred in the hole and let it
there till the silicon hardened.

After hardening I very carefully bend the leg for one of my extruders. For the other 2 I let it straight depends on your extruder type. (avoid that forces gets to the sensor/silicon use two tools)
Then I simple soldered the wires at the end of those legs with no cover.

I have done this for all 3 extruders that I have and have run them at 240 deg without any problem ever.

killejano
Posts: 92
Joined: Mon Apr 01, 2013 7:23 pm

Post by killejano »

Funny thing about the original thermistor is that it has the wires soldered to about 5mm leads and I could melt them with a 305 deg solderin iron :shock:

rad
Posts: 36
Joined: Thu Apr 18, 2013 7:33 pm

Post by rad »

That catched my eye too when I took one of my destroyed sensors apart. If they used normal common solder then I expect it to become loosen during a run since those melt around 200 degree. And if they took higher temperature ones they risk to damage the sensor when assembling. Also I wonder if the fill/silicon is the right one. It looked so flaked that it could support transporting wetness to the sensor. Also the sensor in that metal hull itself didn't look like the one from Farnell with the glass body. I don't know but I lost all trust in them. After I ended up with 3 destroyed already no wonder I guess. If they are not faulty by design or used material then they are too critical to handle in a normal way.

Hugues
Posts: 270
Joined: Thu Apr 04, 2013 5:36 pm

Post by Hugues »

rad wrote:...uring a run since those melt around 200 degree. And if they took higher temperature ones they risk to damage the sensor when assembling..
sorry for the newbie question, but i might have to do this mod, as i bought ABS....

but what kind of solder should i use then ?
Hugues
Regards from Switzerland

killejano
Posts: 92
Joined: Mon Apr 01, 2013 7:23 pm

Post by killejano »

Lead free solder melts at higher temps. I just did mine and the soldering is about 10mm from the hot end. Should not be a problem.

And yes my broken thermistors were also smaller than the ones I got from farnell.

rad
Posts: 36
Joined: Thu Apr 18, 2013 7:33 pm

Post by rad »

Hugues wrote:
rad wrote:...uring a run since those melt around 200 degree. And if they took higher temperature ones they risk to damage the sensor when assembling..
sorry for the newbie question, but i might have to do this mod, as i bought ABS....

but what kind of solder should i use then ?

I took the one that I had at hand and I can't tell you what sort it is. I just thought I try it out and if it doesn't hold I will see it and take another one then or do it different (crimping or something). But it hold.

If you haven't done the mod already make the legs 15mm sticking out of the hole. I wasn't at home when writing that and guessed the length I used. I measured it now and I have 15mm not 10mm. 10mm should work I think but 15mm is certainly better/safer.

About solder there exists so many types. Maybe this table on wiki can help:
http://en.wikipedia.org/wiki/Solder

kimmoli
Posts: 62
Joined: Fri Mar 08, 2013 1:15 pm
Location: Finland

Post by kimmoli »

I routed all the wires "outside", and supported them to the motor, like this: This is to minimize stress on the wires to the head.
http://www.felixprinters.com/forum/down ... &mode=view

t800
Posts: 24
Joined: Sat May 11, 2013 10:28 am

Post by t800 »

I printed the airduct in ABS at 245°C.
After cooldown temperature reading is to low : it reads 5°C and should be 25°C.
And now the printer refuses to start.
Luckely my DIY kit came with a spare thermistor.
But im not expecting to much from this replacement, i also took my precautions ordered 2 "epocs" from farnell.

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