Plastic melting on Duet 2 Wifi heated bed connector
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your connectors dont seem to have ferules on them.
this can happen if the cable is not making proper connection and the surface area of contact is very small.
the cable will heat up due to the restance and melt the connector. -
Yeah, if you don't go back and tighten up the terminals regularly until they're no longer loose that will happen when not using ferrules as recommended.
Odds are the board is fine, you could have just used an external mosfet or had a look at this thread to see if it would make sense to have it fixed. but thb using the external fet is probably far easier than getting parts and dealing with shipping.
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...........and it's always a good idea to re-tighten the screws after a couple of days and thereafter periodically. All as per the instructions here https://duet3d.dozuki.com/Guide/2.)+Wiring+your+Duet/9. If you are handy with a soldering iron, it shouldn't be too difficult to replace that terminal block.
Edit, it seems @bearer and I were typing at the same time but he was a few seconds quicker than me
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its somewhat tricky to get those out without a preheater actually due to the heavy copper. but an oven will work as preheating, but still without practice i'd think odds are traces delaminates and as such using an external mosfet is safer and easier.
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Thanks all! I have a few friends who are handy with soldering irons, so I might draft their help.
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I need to add one more common mistake that results in heating of the connectors (and burning of the plastic casing) and that is "soldering end of the wires). In many European countries, for mains installation, it is strictly forbidden to solder wires. It is not only forbidden to solder end of the wires before you insert them into the terminals but even wire joints can't be soldered, they need to be either twisted or connected using specific "joiner connectors" (like Wago clamps for e.g.). Irrelevant to the European law, you must never tin wires that you are going to push under the screw if there is going to be high current passing through the joint. For low currents (like the heated bed) you have to crimp ferules at the end of the cable, and for high currents (I doubt we have those in 3D printing world) you either use a special crimping tools and connectors (talking about tons of pressure here) or you weld the wire into the connector casing with ultrasonic welder
I too often come across terminals where a person uses stranded copper wire, twist the end and tin it before pushing it into a terminal. Many believe this will create better and safer contact than proper ferule. Because of this wrong belief I'm trying to push the knowledge of how wrong that is and how dangerous those tinned wires under the screw can be.
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what he said
(although didn't look to be an issue in this case, still good spreading the word!) -
I wonder if thermistors on the duet board near the high current connector would help detecting connection issues.
Another approach could be two thin feedback wires from the bed heater, similar to Kelvin shunts but haven't seen any of the shelf bed that come with them.
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@hlawrence said in Plastic melting on Duet 2 Wifi heated bed connector:
The wire must have become grounded on something else,
A bad connection increases the resistance at the connection point and 'steals' power and heat from the bed.
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Classic poor termination - keep those terminals tight - check regularly especially high current connections such as heaters.
