It took two warped ABS prints before I realised my heated bed was failing!

3D Printing
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It took two warped ABS prints before I realised my heated bed was failing! For a month or two I have been running a RAMPS1.4 with the 11 A PTC shorted out and replaced with a 15 A auto fuse, so that I can maintain a 110 degree bed temp for ABS (on a Prusa MK2 PCB bed). However the original mini-TO-220 heatsink was too hot to touch and the black paint burnt off, as can be seen in the first photo. I meant to replace it with a bigger heat sink, but never got around to it, until the FET finally failed.
This may have been exacerbated by my running the heated bed with the Marlin PID controller rather than bang-bang.
Anyway, luckily I had a spare RAMPS board, so I fitted a TO-3P 25mm high heat sink, specially trimmed to fit into the available space, as can be seen in the second photo. Now I am able to touch the heat sink while the bed is maintained (with PID) at 110 degrees, so hopefully it will last for a while.
About to order some spare STP55NF06L s just in case!

Is this a common failure mode with RAMPS?

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pour mois j aurais déporté les 3 TO-220 sur un grande radiateur avec un ventilateur qui refroidi .
se que je suis entrain de faire pour ma version

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I decided to swap the MOSFET for a relay. My bed requires close to 12amps. Although I lose pid, which is not really needes for the bed.

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hi!friends

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@alain_frenois That is a good idea.
I had a fan blowing over the RAMPS, but it was not sufficient. When I have time, I intend to print a frame to hold a full size heat sink above the RAMPS board, parallel to the airflow, with the FET connected to the board using wires.