Heatbed cable cover gone melty all of a sudden  

RE: Heatbed cable cover gone melty all of a sudden

Posted by: @matt-14

[...] I never was a fan of the modded angled cover - I found it to be an almost impossible fit. 

Is that a Prusa part, or a design from another source?

RE: Heatbed cable cover gone melty all of a sudden

It's a remix of the Prusa part, to enable the MK3S to fit into an Ikea Lack enclosure without leaving the door open, as featured in Prusa's blog post on enclosure building: https://blog.prusaprinters.org/cheap-simple-3d-printer-enclosure_7785/

RE: Heatbed cable cover gone melty all of a sudden

Loose nut. Loose nyloc nut. Loose nyloc nut that wasn't loose when I immobilised it in the casing and has been fine for over a year.

Something of a mystery how that managed to happen - Maybe when the cables are put at a slight angle for that cover, it enables them to slowly wobble the connection loose - But easily solved, assuming there are no compounding issues (which of course I'm not going to assume - I've already confirmed the washers were all in the right positions and I'll check the cable before putting it back into use).

With the shorter display panel arms I remixed a while back (that shorten the MK3S's length to match the frontmost extent of the heatbed's travel), I might be able to put the original heatbed cover back on without having to cut a hole in the back of my enclosure for the heatbed cable to poke into.

RE: Heatbed cable cover gone melty all of a sudden

Posted by: @matt-14

I still had an hour to go on a print, but that wasn't an hour I was willing to stand next to my enclosure with a fire extinguisher...

I never was a fan of the modded angled cover - I found it to be an almost impossible fit. My MK3S has been fine for ages with it in place, so of all the possible causes, I doubt it's improper washer placement. I'm hoping it's something simple like a bit of corrosion or a loose screw - If the cable's damaged by trying to cram it into that cover, I guess I'll be putting a third order into Prusa in as many weeks, and doing my MK3S+ refit a tad sooner.

If you have enough space, I would use the original Prusa cover (right angle cable entry). I had a similar problem and made the power supply cables myself from heat resistant and flexible silicone wires (AWG16).

RE: Heatbed cable cover gone melty all of a sudden

My guess would be loose connection, the exact same thing can happen where it connects to the Ensiy board if it becomes loose.

RE: Heatbed cable cover gone melty all of a sudden

There are a couple of centimetres of room in the enclosure with the original heatbed cable cover on, and it's running at a cool 45 degrees C while the bed is holding onto PETG at 85 degrees C. Looking good so far.

RE: Heatbed cable cover gone melty all of a sudden

@swiss_cheese

This is possible.  Make sure you tighten those screws.  This can be a fire hazard.  

RE: Heatbed cable cover gone melty all of a sudden

@cwbullet

Oh, I made sure of that. Those screws are now tighter than Scrooge and Marley.

RE: Heatbed cable cover gone melty all of a sudden

The mystery remains as to why there was suddenly heat in that location after years without problems.  Did you inspect the wires for wear?  It's not rare for insulation to wear off between wires that are being moved back and forth that much.  Alternatively, the thin wires in the wire braids can break from metal fatigue, leading to higher resistance at the points of failure.  You could maybe check for that by measuring it with a milliohm meter.  If you have any doubts, you might want to pro-actively replace the wires with new ones just to be sure.

RE: Heatbed cable cover gone melty all of a sudden

@dimprov

Nearly every case i have had has been due to lose screws on the PSU or Controller board or a broken wire.  

RE: Heatbed cable cover gone melty all of a sudden

Posted by: @cwbullet

@dimprov

Nearly every case i have had has been due to lose screws on the PSU or Controller board or a broken wire.  

In that case, though, the heat would be at the PSU or Controller board, not at the heat bed.  I suppose the connection where the power wires connect to the PCB heat bed could have become worn if there were any play in it. 

Alternatively, maybe the solder mask on the PCB wore through and the build plate is shorting near there, creating a hot spot which gets conducted into the power cables?  I've noticed the solder mask on my PCB heat bed slowly wearing away over time, exposing the PCB traces underneath.  I doubt I'm alone in that, as it's just mechanical wear/abrasion from many cycles of attaching/removing the magnetic build plate.

RE: Heatbed cable cover gone melty all of a sudden

@dimprov

Not 100%.  I have never had a PCB issue in 16 printers.    

RE: Heatbed cable cover gone melty all of a sudden

16 printers!  In that case, I guess the reason is probably what you said.

Wow.  Where do you even put them all?  Since this thread seems to have run its course already, I just have to ask: which ones do you have, and why so many?  

RE: Heatbed cable cover gone melty all of a sudden

@dimprov

I have a small farm with 23 acres.  I have them in an outbuilding.  

I am just saying to check the wiring.  2 near fires.   1 melted set of wires.  One on the bed and one on the controller board.   I had to replace the controller.  Two were loose connectors and one was a broken wire.  

RE: Heatbed cable cover gone melty all of a sudden

@charles

I've had both of those happen, I always check them now as part of general maintenance, I was lucky and caught the problems before they became bigger issues. 

RE: Heatbed cable cover gone melty all of a sudden

@swiss_cheese

Just curious now. How old are the printers with the wire and connector problemen? And after how many hours did that happen. 

RE: Heatbed cable cover gone melty all of a sudden

@baklin

Assembled at the beginning of September 2019, currently 51D 11H 33M on the printing time tally.

RE: Heatbed cable cover gone melty all of a sudden

@swiss_cheese

Good point.  

RE: Heatbed cable cover gone melty all of a sudden

Posted by: @baklin

@swiss_cheese

 

Just curious now. How old are the printers with the wire and connector problemen? And after how many hours did that happen. 

Now, 3 yrs old. the trouble with the cable on the Ensiy board happened first year and was noticed after receiving errors from the machine, loose screw at the connection had caused the connection at the board to heat up to the point it was melting. The next was a little over two years in, it happened from a break in the wire near the heated Bed, I noticed while watching a print that the Part that clamps the wire was starting to deform slightly, so I touched it and it was way hotter then it should have been so I stopped the print and ordered new cables. now I just take a look at these areas as a course of best practice. I don't fault the equipment its been used for countless hours, things wear out.