My heated bed tried to self destruct.

The bed itself is fine, but the wiring SERIOUSLY overheated for some reason. It was super strange though, because it didn't burn the 10A fuse that was in there, the wires and terminal just stated melting. And I was only running it at 55c while printing some larger PLA parts.

I saw little wisps of smoke that I though I was imagining at first, until I looked a bit close, and found this.



Looks like it's time for a rewire. I think I'll just disconnect it until my Mk2 kit gets here. No point in fixing it, just to replace it.

Wowzer that was lucky.

What Gauge wire are you using for the heat bed?

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Out of the box thinking is easier when you never fitted in the box to begin with.

Bad connections cause resistance which causes heat then that causes worse connection which is more resistance and thus more heat. So this is caused by the connection starting to be bad and it snow balls from there. If you are going to use those screw terminals be sure to check them for tightness every once in awhile. A little loos or a little corrosion and this is what you end up with.

Quote
tmorris9
Bad connections cause resistance which causes heat then that causes worse connection which is more resistance and thus more heat. So this is caused by the connection starting to be bad and it snow balls from there. If you are going to use those screw terminals be sure to check them for tightness every once in awhile. A little loos or a little corrosion and this is what you end up with.

Eh, just when I mounted similar screw terminals on my setup... Any suggestions for a better type of connector? Preferably one that would not need much maintenance, but still provide means of disconnecting for upgrades and whatnot...

Good that you post this, hopefully it can teach and prevent it from happening to someone else.

Any way as pointed out, the origin of the heat is quite clearly seen to be from the screw terminal.
In term of current capability for these they normally range from 5A and up depending on size.
but certainly it's depending on the actual contact. You can also use ferrules to further improve contact.

First of, what kind of current is needed for you heat bed?

For best performance, do away with the blocks and connect direct to the main board terminals

Well in my case, I am using a 220V AC 800W heater, which came with ~30cm long leads and I need some way of extending them. So far I was under the impression that these screw terminals are a really good solution... guess not...

What voltage is your bed running at, and how is it wired up? I'm not sure I understand the wiring in the photo.

I quite like the EC3 connectors for high current hookups, they are relatively easy to put together, polarized and fairly compact for the current capacity:

[P4AAMXQrNtR041m" target="_blank" rel="nofollow">www.ebay.ca]

If you use screw terminals for high current it's a good idea to put ferrules on the wires (get the right size for the wire you use):

[www.ebay.ca]

[Edit: the above is for low voltage connections, not for AC mains]

Edited 1 time(s). Last edit at 10/20/2016 01:48PM by JamesK.

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Dalius98
Well in my case, I am using a 220V AC 800W heater, which came with ~30cm long leads and I need some way of extending them. So far I was under the impression that these screw terminals are a really good solution... guess not...

Um, well my sugestion wont work as the boards are only 12v.....

By my count it wont blow a 10A as its only around 3.6amps!
Strange.

As others have said, you need to periodically check your connections and maybe fit a smoke detector to the printer that will disconnect the supply.

I got a ceramic block, but there is higher amp versions of yours, i'm also using wago clips but would also look to change for something more plug n play, I could do with some ferrules though.

Quote
Dalius98
Well in my case, I am using a 220V AC 800W heater, which came with ~30cm long leads and I need some way of extending them. So far I was under the impression that these screw terminals are a really good solution... guess not...

These terminals work fine and are found in electrical junction boxes at mains voltage almost everywhere. As pointed out the current at 220v is very small and could probably pass through a very narrow cable quite safely. But if you've got some normal sized mains cables use them and these terminals.

Low voltage heaters are a risk, the current is going to be high if you want 12v to heat a 200x200mm bed to 120 deg C. To the Op twist your wires together well (see the lineman's splice) and solder your wires together with heat shrink tubing around them.

You're using automotive blade fuses. I use one too on my 24v 12A heated bed, at one point a fuse melted, not the wire but the plastic around the fuse. The fuse was 15A I run 12A through the bed heater (maximum of my 24v supply), swapped it for a larger fuse now no problems. One wire with a soldered joint is warm to touch but never hot.

Edited 2 time(s). Last edit at 10/20/2016 04:10PM by DjDemonD.

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Simon Khoury

Co-founder of [www.precisionpiezo.co.uk] Accurate, repeatable, versatile Z-Probes
Published:Inventions

Old problem, those screw terminals melt very easily...

... old school solution.

[en.wikipedia.org]

Wow, lots of replies while i was at work.

So it's a 12v 300x300 bed, and I'm not sure what the terminals are rated at because I installed them almost 2 years ago, but they are clearly what went wrong.

The terminal blocks seemed like a good idea for serviceability, and they are on all of the major wire runs. I'll probably leave them for the motors, but I won't be using them for the heater again. Though, in fairness, it probably wouldn't have been an issue of I'd been checking that connection regularly (it had been chugging along for years before this problem happened).

Also, that wire comes straight from the power supply, and there's is a relay just to the right of the picture. So only the coil is pulling from the RAMPS. I'll be replacing/ rewiring the whole thing when my Mk2 kit gets here and I upgrade to the RAMBo-mini to control it all. Until then I'm just going to leave it disconnected.

At that point, I'm debating whether to re-use this pad on my CubeX project, or upgrade to a 120v heater with an SSR for PID control.

A good crimped connection is best but not as convenient. If you want to be able to remove it you might consider some of the hobby 2 prong plug connections, they are designed with low voltage high current in mind (some can take 35-50 amps) I like EC3 connectors myself but only the 'real' ones, lots of fakes that won't hold 1/4 of the amperage.