Melzi Hotbed connector fried!

Was printing rather a lot today and noticed a strange smell coming from the region of my printer... it smelt like burning (surprising you might say when you are heating filament to 250 degs), but this smell was different!

I had a sniff around the printer and noticed the smell was strongest from the area of the power supply... great burnt out PSU was my first thought, but everything was still running fine... then I noticed the Melzi... see the attached pictures!

So question is... why did this happen now (been printing at the same hotbed temps for ages (I get my hotbed to 135 degs read on the sensor - that equates to about 110 on the glass on top).

Also can I just solder back in another connector block and re-fit everything? or should I look to ramp up on the connector size to carry more Amps?!

Cheers,
Terry.

My suspicion would be that it was caused by a loose connection. So I would just replace the connector and see what happens.

Hi,

a few days ago I noticed that my heatbed was not heating. I discovered a loose screw on the Melzi board. I was sure that I screwed the cord tight. I can only asume, that "something" looses the srew. Maybe the fibration during print ... I don't know. Since then I check everey few days all the screws on the Melzi.

Removing the terminal screws and cleaning the board from all melted plastics should give you a reasonable hint if it could live further with new terminal screws.

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MfG / Regards

Stefan

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Blog / Gallery / Wiki / Mendel90 kit since Sep 2013 from Nophead / Original Prusa I3 MK3 since Feb 2018 /
OpenScad Workshop: Kursdateien
Octoprint Patron since April 2016

If vibration is the cause, consider applying high temp silicone to the screw.
I wouldn't use hot melt glue, as it would be a fuel for a fire.

From what I have read:
Type I silicone reacts with water. I believe type I releases acetic acid during setting (smells like vinegar), and this is corrosive to metals.
Type II silicone reacts when water is removed, or is activated by a different means, ("Oxeme" cure and release oxemes and methyl alcohol).

Some one with experience in this field should verify.

What kind of glue should I use for PCB-mounted components to avoid vibrations?
[electronics.stackexchange.com]

A2

I have never had any screw terminals fail. That is why I use them as I have had many friction fit connectors fail on reprap machines. I think it is just a matter of tightening them properly.

After some comments in these forums I no longer recommend tinning the wires in the manual, but having said that I have always tinned mine and never had an issue. The theory is solder can creep over time so they can become loose. Maybe tinning with an excess of solder is the problem.

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[www.hydraraptor.blogspot.com]

Lots of vibration solutions for 3d printers on Thingiverse.
Maybe there is a problem...

[www.thingiverse.com]
[www.thingiverse.com]
[www.thingiverse.com]
[www.thingiverse.com]
[www.thingiverse.com]
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[www.thingiverse.com]
[www.thingiverse.com]
[www.thingiverse.com]
[www.thingiverse.com]
[www.thingiverse.com]
[www.thingiverse.com]
[www.thingiverse.com]
[www.thingiverse.com]

LOL... I actually printed a set of these...

[www.thingiverse.com]

Then promptly gave them to QuackingPlums!

Maybe I should have printed myself another set!

Terry.

bastard Wrote:
-------------------------------------------------------
> Hi,
>
> a few days ago I noticed that my heatbed was not
> heating. I discovered a loose screw on the Melzi
> board. I was sure that I screwed the cord tight. I
> can only asume, that "something" looses the srew.
> Maybe the fibration during print ... I don't know.
> Since then I check everey few days all the screws
> on the Melzi.
>
> Removing the terminal screws and cleaning the
> board from all melted plastics should give you a
> reasonable hint if it could live further with new
> terminal screws.

Removed the parts that were left of the terminal block (the block broke up when I tried to unscrew the screws), and de-soldered the pins out of the board (and used a solder sucker to clean out the holes).
Results shown in the attached pictures, everything looks like it has got a bit hot!

nophead Wrote:
-------------------------------------------------------
> I have never had any screw terminals fail. That is
> why I use them as I have had many friction fit
> connectors fail on reprap machines. I think it is
> just a matter of tightening them properly.
>
> After some comments in these forums I no longer
> recommend tinning the wires in the manual, but
> having said that I have always tinned mine and
> never had an issue. The theory is solder can creep
> over time so they can become loose. Maybe tinning
> with an excess of solder is the problem.

Thanks Chris, these wires weren't tinned I don't think, but they are so black and charred now it's difficult to tell!

Will Tin them this time (lightly).

New connectors on their way and should be with me tomorrow, fingers crossed it all still works fine (the board boots, but worried about the hot bed circuit), maybe time to look at a Mains hotbed, Chris any pointers?

Thanks,
Terry.

I wouldn't recommend a mains bed for amateur construction.

There is no problem with the bed terminals if they are tight enough. The power connector has more current through it and heating is a square law so if that has survived it must be a much better connection.

I would not recommend putting any extra wires in the power connector like that. The connections have to be really low resistance to not get hot. I.e. a no more than a few milliohms. To put that into context multimeter leads have a typical resistance of 0.1R each. If it was has high as say 0.01R it would dissipate 2.56W at 16A and in such small device would get significantly hot.

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[www.hydraraptor.blogspot.com]

Just out of curiosity I checked through all my Melzi screw terminals and some had become looser than their initial tightness.

In my case also the Bed Heater connection was looser than initially set. It looks like regular checks on these might be advisable as part of routine maintenance.

Regards,
Neil Darlow

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I try to write with consideration for all nationalities. Please let me know if something is unclear.
Printing with Mendel90 from fedora 25 using Cura, FreeCAD, MeshLab, OpenSCAD, Skeinforge and Slic3r tools.

nophead Wrote:
-------------------------------------------------------

> I would not recommend putting any extra wires in
> the power connector like that. The connections
> have to be really low resistance to not get hot.
> I.e. a no more than a few milliohms. To put that
> into context multimeter leads have a typical
> resistance of 0.1R each. If it was has high as say
> 0.01R it would dissipate 2.56W at 16A and in such
> small device would get significantly hot.

Good point well made Chris! Thanks for pointing that out, and it proves what can happen if the connectors are "loose" and have resistance in the results of my Hot Bed connector issues.

I'll look to splice into one of the 12v lines for my feed to my Panelolu2 12v switched devices (LEDs and Fan), and into one of my Ground Wires for my returns from those devices!

Cheers,
Terry.

Quote
Chargenut
LOL... I actually printed a set of these...

http://www.thingiverse.com/thing:94733

Then promptly gave them to QuackingPlums!

Maybe I should have printed myself another set!

Terry.

You can have them back if you want Terry - as I mentioned in this thread, after spotting the effect that having a less-than-level bed has on your first layer adhesion I re-measured mine and realised that I was also suffering from it, albeit to a lesser degree. Removing those feet gave better results and reducing the acceleration in my start gcode more or less eliminated the shaking I was getting anyway

Okay good points to note... I've added the acceleration change code to my start code now anyway, so maybe that will be enough to reduce my vibrations.

I'll give the feet a miss for the moment!

Terry.

New connector has now been soldered into the Melzi and have just run a test bed heat up first to 80 degs (check for smoke/heat/smell - all good) then to 135 degs.

All fine... I'm ready to start printing again!!!

Terry.

i just had the same problem on the exact same connector!!! where did you get another connector from?

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sixdollaftlong
i just had the same problem on the exact same connector!!! where did you get another connector from?

http://www.rapidonline.com/Cables-Connectors/Connectors-Terminal-Blocks
http://www.maplin.co.uk/productsearch?criteria=terminal+block

Same issue here. I picked a spare from maplins which is a touch taller than the original but works fine.

Does seem a common 'user error' with the Melt-z. It needs a proper connector block that wont work loose and/or a fuse!

The issue I have post burn-out is that the HB mosfet runs hot. So I have the extra fan pointing at the pcb to keep it cool when the HB is on. Seems to work so far!

Very odd. Nobody has reported a bed connector failing and then three altogether.

A few people have melted the power connector but that has all the bed current plus about 4A so should get 1.4^2 times hotter. I.e. about twice as hot if the contact resistance was equal. Neither get noticeably warm on my machines, one of which has been running continuously since the start of kit production and I have never needed to re-tighten the connections.

Also the bed MOSFET doesn't normally get any more than slightly warm as it has a very low on resistance.

Quote

It needs a proper connector block that wont work loose and/or a fuse!

It does have a proper connector block and a fuse would be no help at all. When the contact resistance increases, such that the connector gets hot the bed current reduces so a fuse is not going to blow.

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[www.hydraraptor.blogspot.com]

Perhaps the 3d printer has developed to a stage wherein morphogenetic fields are created.
[www.sheldrake.org]
Smiley follows :-)