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Heatbed thermistor wire repair  

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Coyoteran
(@coyoteran)
Active Member
Heatbed thermistor wire repair

Hi all.  

I have been getting intermittent heat bed failures for about 4 months now. It turns out I had a broken wire just where the thermistor wire passes into the fabric wrap. It would make contact most of the time but occasionally it would lose contact and kill the job.

I cut out 4cm of wire around the offending piece and soldered in a replacement using standard HRS techniques. The unit now works but my question is have I set up something else to fail. Is the thermistor calibrated to the included wire? The wire gauge is the same and the length is within 2mm of the original. 

Or am I overthinking this?  Thanks.

Trevor

Posted : 30/01/2021 6:35 pm
JoanTabb
(@joantabb)
Moderator
RE: Heatbed thermistor wire repair

Hi Trevor, 
this is a thermistor  setup, which is a lot more forgiving than say a thermocouple. 

at 25Centigrade the thermistor resistance will be in the order of 100 000 ohms, so a change in resistance in the copper wire of micro ohms, or even milli ohms, will not make a measurable difference. 

at working temperatures 180C to 280C the resistance varies between 680 Ohms' and 110 ohms' so again a tiny change in wiring resistance is unlikel to cause a significant difference in performance

regards Joan

I try to make safe suggestions,You should understand the context and ensure you are happy that they are safe before attempting to apply my suggestions, what you do, is YOUR responsibility. Location Halifax UK...
Posted : 30/01/2021 6:45 pm
Coyoteran liked
cwbullet
(@cwbullet)
Illustrious Member
RE: Heatbed thermistor wire repair

I just buy a new one.  

--------------------
Chuck H
3D Printer Review Blog...
Posted : 30/01/2021 8:18 pm
Coyoteran
(@coyoteran)
Active Member
Topic starter answered:
RE: Heatbed thermistor wire repair
Posted by: @cwbullet

I just buy a new one.  

So would I if I lived someplace where I could buy it locally or not have to wait 4 weeks for shipping. Moose Jaw Saskatchewan is not exactly a hotbed of technological development and commerce. 🙂 I went to three local computer stores trying to source a 30mm fan for a Raspberry PI and every single one of them asked me what a Raspberry Pi was. One asked me if it was a new Apple product. 

Posted : 30/01/2021 8:49 pm
cwbullet
(@cwbullet)
Illustrious Member
RE: Heatbed thermistor wire repair

@coyoteran

That is funny.  

--------------------
Chuck H
3D Printer Review Blog...
Posted : 30/01/2021 9:14 pm
JoanTabb
(@joantabb)
Moderator
RE: Heatbed thermistor wire repair

Hi Trevor, 

I would suggest that you buy some flexible silicone insulated cable, it is excellent for repairing printer cables, and it is unlikely to go faulty again...


I use 16AWG for heatbed power cables, 

and 22 or 24AWG for other wires
another common failure is the Pinda Wire,   Mk2 has 3 wire cable, as does the Minda and Superpinda. the Mk3 has a 4 wire cable, 


regards Joan

 

I try to make safe suggestions,You should understand the context and ensure you are happy that they are safe before attempting to apply my suggestions, what you do, is YOUR responsibility. Location Halifax UK...
Posted : 30/01/2021 9:25 pm
Coyoteran
(@coyoteran)
Active Member
Topic starter answered:
RE: Heatbed thermistor wire repair

So the plan (idea?) is to do a major overhaul to the Mk3s after prusa comes out with, and I buy, a corexy machine. I have over 400 days of print time on the 3s with the original bearings and steppers. Rewiring the moving bits with the silicone covered wire is now on the list. 

Back in the day I used to repair analog telephones. The curly cords for the handset had fabric interwoven conductors, the name of which escapes me. They were a bitch to solder to pins but the cords themselves never broke. Initially I was going to try and source that stuff to replace the thin moving wires. Thankfully there is a better way.

Posted : 30/01/2021 11:31 pm
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