Well it had to happen sooner or later...

posted 30 Sept 2012, 05:20 by Colin Bell   [ updated 30 Sept 2012, 05:20 ]
...and now it has. The connections that make up the heated bed circuit on the Huxley failed last night. The issue seems to be that the constant high temperatures cause the ferrules to oxidise, and create a bad connected on between the power wires and the Nichrome heating element. This, combined with the bed movement makes this a weak point in the assembly.

After peeling back the shielding on the bed, I could clearly see the scorching and melted heat shrink and badly oxidised wires and ferrules. Fortunately, the Kapton tape had not been affected, so I wasn't getting any dangerous shorts. Gotta love that Kapton!

I was thinking that perhaps the MOSFET had failed on the controller board, but after seeing this, I could see that this was't the case. I did test output on the board, and it was maintaining 19V - although I must have misread it, as it seemed to do this as soon as the board was powered, and not only when the MOSFET was commanded to engage...I must investigate this further as if this was the case the bed would remain powered all the time, which it does not. It was quite late, so perhaps I just misread...

After a bit of a clean up, I replaced the ferrules with some beefier versions I had spare and reassembled. The heat bed is now working again, and also is heating much faster and maintaining it's temperature in a more stable manner, so I guess this repair is as much an upgrade as a fix!