Thermistor Fail

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printer999
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Thermistor Fail

Post by printer999 » Wed Dec 10, 2014 5:40 pm

ok, So I pretty much killed my old hotend. (thermistor) So I ordered a e3d v6 hotend and assembled it and made my own makeshift mount and such today. I soldered all the wires including the thermistors to the wires that were previously there for the old hotend. My question was, when I turned on the printer for the first time since I replaced the hotend, The printer still had no reading on what the heat for the hotend was. Is this likely because of faulty wires leading to the thermistor?

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Re: Thermistor Fail

Post by precisionpete » Wed Dec 10, 2014 6:10 pm

Depends on how hot you got that little wire when you soldered it.
I used the crimps but even then you have to make sure it gets a good connection since the wire is so small.
Either bad connection or you fried it.

Remove a lead so your not connected to the rambo and check the resistance, should be 100K ohms.

Tip which I plan to do next time I take apart everything which could be any day :) Grab some small connectors and solder everything up so you can take apart and test easier.

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Re: Thermistor Fail

Post by bvandiepenbos » Thu Dec 11, 2014 9:49 am

I hear that the new Marlin firmware has protection for failed tmist/run away heating.
But most people are running Repetier fw on their SeeMe machines, so that is not much help.
Does anybody know if Repetier fw has this feature?

I don't know much detail, but I gather it watches for temperature change if temp does not rise within a set time (40 seconds I think) it shuts everything down. assuming tmist failed.
Sounds like a REALLY good feature, paticularly if running the SeeMe hot-end with the silly RTV glued in tmist!
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Re: Thermistor Fail

Post by RocketMagnet » Thu Dec 11, 2014 1:05 pm

I was wondering about exactly the same thing.

Seems pretty simple to me on the face of it but you'll need to capture a number of fail states so know how the thermistor can fail and what the outputs are.
Sounds really easy to cover a Zero output or a max output and account for them, also the heat up cycle rate of change and if your average output over
a fixed timeframe while at target temp is 100% to cover a "locked" value.

However if your wanting to be safe the temp cut out and monitoring should be independent of the control. So this would mean another thermistor or thermocouple to compare. If they don't agree within a range.. cut the power.

But agree totally I don't see why the easy cases aren't covered in software... e.g. zero or max thermistor outputs. The rate of change stuff is more complex as it's state dependant. I've really not got the time to try atm, I've scanned the code and made some changes but I find it tough to follow in places... so implementing this requires a good knowledge of the code and being realistic the possible legal issue if it fails to protect?

I'm pretty sure thermistors don't have polarity so its irrelevant which way you wire them up. I'd certainly check for continuity with a multimeter from your Rambo end to your hot end.

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Re: Thermistor Fail

Post by jdurand » Thu Dec 11, 2014 1:11 pm

A fairly simple test:

When temperature reaches set point +/- something %, set flag.

In operation if flag then if temperature is more than something bigger % off set point, panic.
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Re: Thermistor Fail

Post by printer999 » Thu Dec 11, 2014 3:13 pm

so, back on topic. Any ideas? The Lcd is reading def whenever I plug the lead for the thermistor in, besides that the fan always starts running when I plug it in.

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Re: Thermistor Fail

Post by Earthbound » Thu Dec 11, 2014 4:12 pm

I think I remember that def is an indication of open thermistor circuit, so either unplugged, broken wire, or bad thermistor.
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Re: Thermistor Fail

Post by Mac The Knife » Thu Dec 11, 2014 6:23 pm

printer999 wrote:so, back on topic. Any ideas? The Lcd is reading def whenever I plug the lead for the thermistor in, besides that the fan always starts running when I plug it in.


Which fan starts running when you plug what in? The Peek fan starts running when you plug the thermistor in?
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Re: Thermistor Fail

Post by SoCalSteve » Thu Dec 25, 2014 4:29 am

I've been running my Rostock since late October. It's my first printer, but I have over 13 hours of run time. I upgraded to the E3D V6 a couple weeks ago and have been running mostly PLA and BronzeFill. Very recently I will be printing and I'll get "def" for my nozzle and bed temperatures. I thought it was a bad thermister, but was puzzled when it affected my bed as well.

Sounds similar to the OP's issue. Any suggestions?

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Re: Thermistor Fail

Post by Eaglezsoar » Thu Dec 25, 2014 8:06 am

A def indication is indeed an inability to read the thermistor.
This is usually caused by a loose wire to the thermistor.
To check turn off power and unplug the thermistor from the Rambo and with an ohm-meter measure
the resistance of the thermistor, at room temperature the thermistor should read approximately 100K.
If yours does not read that value then you have a problem with wiring or a defective thermistor.
Bad wiring is the most common.

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Re: Thermistor Fail

Post by Noob » Tue Dec 30, 2014 11:15 am

This just happened to me too last night. Same circumstances, 13 hours and 16 minutes of run time, recently upgraded to E3D v6, which I have gotten some prints out of then all of a sudden both bed and nozzle went to "def."

I will check the wiring/resistance, and let you know what I find :evil: :twisted: :oops:

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Re: Thermistor Fail

Post by SoCalSteve » Tue Jan 06, 2015 2:13 am

Eaglezsoar wrote:A def indication is indeed an inability to read the thermistor.
This is usually caused by a loose wire to the thermistor.
To check turn off power and unplug the thermistor from the Rambo and with an ohm-meter measure
the resistance of the thermistor, at room temperature the thermistor should read approximately 100K.
If yours does not read that value then you have a problem with wiring or a defective thermistor.
Bad wiring is the most common.

This isnt a constant issue. I have gone up to, but not exceeded 300C could that be the issue?

Ive been looking at the Type K Thermocouple and the External Thermocouple Board. I'm wondering if anyone has experience in this area and can tell us if replacing the thermistor with these two items will yield successful results? Obviously the required temperature setting would be required in the programing as well...

Any help on this would be greatly appreciated!

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Re: Thermistor Fail

Post by BenTheRighteous » Tue Jan 06, 2015 10:21 am

SoCalSteve wrote:This isnt a constant issue. I have gone up to, but not exceeded 300C could that be the issue?

Could be. The instructions tell you not to go above 295 or else you'll damage the thermistor. I don't know how strict that is, or how much wiggle room there is (if any).
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Re: Thermistor Fail

Post by Noob » Wed Jan 07, 2015 2:48 pm

SoCalSteve wrote:
Eaglezsoar wrote:A def indication is indeed an inability to read the thermistor.
This is usually caused by a loose wire to the thermistor.
To check turn off power and unplug the thermistor from the Rambo and with an ohm-meter measure
the resistance of the thermistor, at room temperature the thermistor should read approximately 100K.
If yours does not read that value then you have a problem with wiring or a defective thermistor.
Bad wiring is the most common.

This isnt a constant issue. I have gone up to, but not exceeded 300C could that be the issue?

Ive been looking at the Type K Thermocouple and the External Thermocouple Board. I'm wondering if anyone has experience in this area and can tell us if replacing the thermistor with these two items will yield successful results? Obviously the required temperature setting would be required in the programing as well...

Any help on this would be greatly appreciated!



Hey! I have not had the chance to dive into this problem on my machine yet. All I know is that both thermoistors blew at the same time, and at relatively low temps. The bed was turned off when this happened to me, and the nozzle MAXTEMP was set to 285. E3D states this is top end of the termoistor operating range. I too was interested in the Thermocouple and External Board, but then I read this....

http://forum.seemecnc.com/viewtopic.php?f=77&t=6986&p=55490&hilit=external+thermocouple#p55536

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Re: Thermistor Fail

Post by SoCalSteve » Fri Jan 09, 2015 12:11 am

BenTheRighteous wrote:
SoCalSteve wrote:This isnt a constant issue. I have gone up to, but not exceeded 300C could that be the issue?

Could be. The instructions tell you not to go above 295 or else you'll damage the thermistor. I don't know how strict that is, or how much wiggle room there is (if any).
Ah. See on the v6 page it states "High Temperature Peformance. With no PEEK or PTFE in hot regions of our HotEnd we can reach 300C with the supplied thermistor. By swapping a thermistor for a thermocouple (may require additional electronics) you can reach over 400C." and took that as gospel.

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Re: Thermistor Fail

Post by BenTheRighteous » Fri Jan 09, 2015 9:42 am

Yeah, shame on E3D for not being consistent.

http://e3d-online.com/E3D-v6-Assembly

The second last step says:

Set the HotEnd temperature to 285ºC. If you did not do a PID tune, then approach this temperature slowly, exceeding 295ºC will permanently damage the thermistor.
nitewatchman wrote:it was much cleaner and easier than killing a chicken on top of the printer.

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