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Heatbed cover melted.  

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bracco23
(@bracco23)
Active Member
Heatbed cover melted.

Hi,

I just noticed that the plastic cover for the heated bed cable was melted. I had to break it and pry it off to expose the cable and see that the GND cable was overheating and melting. What is the cause? The mini is a mini kit I assembled myself about a month ago. I know usually the problem is the assembly not done correctly but the cable were in the correct position, can't vouch for the tightness though. The bed seems to be more or less intact, except for a few scratches done during prying and a corner of the negative pad lifting of the PCB.

 
This topic was modified 1 month ago by bracco23
Posted : 23/06/2021 9:00 am
cwbullet
(@cwbullet)
Illustrious Member
RE: Heatbed cover melted.

Be careful.  If it is overheating, it could be multiple items to include a loose connection for the bed wires.  A loose connection will increase resistance and heat up.  Fire is the end possibility.  

--------------------
Chuck H
3D Printer Review Blog...
Posted : 23/06/2021 9:05 am
bracco23
(@bracco23)
Active Member
Topic starter answered:
RE: Heatbed cover melted.

For now I unscrewed everything and I'm keeping it on hold until I fix it, I am definitely not going to use it in this condition unless I have a good idea of the cause.

Posted : 23/06/2021 9:14 am
Baklin
(@baklin)
Reputable Member
RE: Heatbed cover melted.

A loose connection will cause that.

 

Replace the wire as it has been very hot too. I wouldn't trust that wire any more.

 

And install the new wires with new screws and nuts. 

After that keep an eye on it to make sure it doesn't get hot anymore. The bed should be fine, but you want to make sure it is over the first prints.

 

Maybe contact Prusa support to see if there is any warranty even though you build the kit.

Posted : 23/06/2021 10:48 am
sjbolton
(@sjbolton)
New Member
RE: Heatbed cover melted.

Definitely a short. I’m soon to purchase a Mini so I dont have experience with this printer yet, but a bunch of other brands.They mostly have a similar problem with the cabling to the heated bed not having strain relief. In your case it could be a poorly crimped lug but Prusa prides on quality and reliability in his printers and I doubt this is the cause here. The lugs not being tightly fixed is certainly a probable cause. Lastly is how you’ve tidied the cable or constrained it. Wires are very very very thin and it only takes a few bendings before the metal fatigues causing crack/breaks this creates the short that turns a wire into a heating wire causing the melting and eventual fires. So as the bed moves the wire gets bent close to where its secured, if you’ve inhibited the rest of the cable from moving freely (due to fear it will catch and stop the bed moving perhaps?) that can contain the wire bending even more to a small area. I’ve seen many people cable tie their bed cables to keep them out of the way or use a weight to hold them down on the table so they aren't moving around. No idea about how you’ve treated yours its commonly overlooked by people just how fragile wires are to bending. Did you move your printer a lot? “Portable” printers are very fragile to  wire damages. My gut says this is not a manufacturer defect though. You really need to contact Prusa support for advice.That power cable needs to be tossed, its ruined now, the breaks will still be there and carbonisation will have added resistance ( another fire risk) inside the cable sheathing. The contact pad on the bed looks to have started to lift at its corners creating another increase in resistance and fire hazard. I don’t know the construction method (electrical path through the board etc) so you must contact Prusa for advice , I expect the bed and wiring now requires replacing, it may work for a little while  in its current state and Prusa should be able to tell you if its safe. But I doubt they will, electrical shorts cause a lot of unseen damage, it only takes a wire being bent once or twice for a wire strand to crack inside the length of wire for a short to occur and fire to be likely. You can’t know or check . So contact them for advice, there may be some sacrificial parts or fuses or voltage test pads that you could test safely with a multimeter to see if there is damage elsewhere. Electrical circuits  work as a whole and when one part fails it can overload another part of the circuit causing more damage. Fuses are used to help protect and isolate parts of the circuit from a domino effect of failures. Ever seen areas of a country lose all electricity because an accident or bushfire  destroyed a large distribution transformer causing too much power to flow in other areas of the electrical grid, causing more transformers to blow and more blackouts and on and on. Speak to Prusa for advice, not a forum, they need to know in case other have had problems, together it may point to a bad batch of wire or incompetent employee, but whatever your printer is currently a fire hazard I’m sure Prusa would help you out with replacing parts and what to check to make sure you’re safe, if you want to be cheap and avoid talking to them then safe time and harm and bin your printer now, its not worth the risk trying to think you can fix it .

Posted : 23/06/2021 11:20 am
bracco23
(@bracco23)
Active Member
Topic starter answered:
RE: Heatbed cover melted.

I have already contacted support and showed them this post, they said they will have an investigation internally and will let me know. Definitely not going to use the printer, I will leave it as it is until they let me know.

Posted : 23/06/2021 11:28 am
sjbolton
(@sjbolton)
New Member
RE: Heatbed cover melted.

Thats good. 3D printers are full of unforeseen issues, its not as simple a technology as a toaster and we’re still in a learning stage. Its all part of the learning process we all go through, unfortunately its all negative experiences we really get. No need to ask for help when everything runs well. I dont think any manufacturers yet are close to having every possible problem anticipated and pre-fixed in their printers. It still a tinkers kit time. Can be frustrating but I think Prusa will look after you, not like the Chinese vendors that I’ve had nothing but garbage excuses and finger pointing with my other printers.You’ve had a lucky close call, a fire could have done much worse so I hope you get up and running sooner rather than later. The Mini has a bunch of electronics safety features, its likely one of those kicked in to cut power before the overheating continued long enough for fire to start. Good luck with it all mate!

Posted : 23/06/2021 1:04 pm
Baklin
(@baklin)
Reputable Member
RE: Heatbed cover melted.
Posted by: @sjbolton

Definitely a short. 

Not a short.  A bad connection = high resistance in that connection = heat.

Posted : 23/06/2021 2:11 pm
cwbullet
(@cwbullet)
Illustrious Member
RE: Heatbed cover melted.

@baklin

This is what I suspected.  I have a had connection or loose wire that almost led to a fire.  

--------------------
Chuck H
3D Printer Review Blog...
Posted : 24/06/2021 1:22 am
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