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puremoco

Short circuit on heatbet

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Hello,

I started a print like usually and then notice some bad smell and smoke from the heat bed connector:

IMG_20170530_213801295.thumb.jpg.0fde174a984a0aa6815d2a636354c2b6.jpg

IMG_20170530_214346970.thumb.jpg.c0869721af33a06dbf20672c0b2c66fe.jpg

IMG_20170530_214325403.thumb.jpg.2522c100ee7cd4f2105245e6f900bcb4.jpg

I guess there was a short circuit between the heating wires. They are melted together and also melted the connector on the heat bed.

How can this happen? The printer has around 3.000 printing hours, but such critical component should not get damaged over time. Luckily I have noticed it and stopped the printer, otherwise there might be fire starting...

Why are there no wire-end sleeve used? Why is the PCB/firmware not detecting such short between those wires and stopping the printer? Those are really necessery safety features if you are dealing with high current.

A new heatbed costs around 180€. So I would like just to replace the screw-connector on the heatbed. Does anyone know the part-number of the connector?

IMG_20170530_213801295.thumb.jpg.0fde174a984a0aa6815d2a636354c2b6.jpg

IMG_20170530_214346970.thumb.jpg.c0869721af33a06dbf20672c0b2c66fe.jpg

IMG_20170530_214325403.thumb.jpg.2522c100ee7cd4f2105245e6f900bcb4.jpg

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That is some seriously scary shit right there.

I'm not an electrical engineer but the resistance of the heatbed should be around 5 ohms plus maybe one ohm in the cable to err on the high side. Making a detection circuit that can reliably differentiate between 6 ohms and 1 is probably pretty hard.

I'm trying to find the connector but it doesn't seem to be documented and google is turning up nothing. I measured the pitch on my printer but couldn't make it out perfectly without disassembling the bed. It looks like it should be 3.5mm. Could you measure on your bed?

Cheers

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