Hello, I have the Reprap i3 for over a year now, for most part it works well. But then this happened recently. The green terminal to the extruder and heated bed got extremely hot, and it was burning. as in the attached pic. Why is that?

i donthave no experience with ramps but i think there are two reasons why this happened. the first one is that the cables were loose . and i think that you have to drive the heatbead with a relay as the amps are much for the board itself.

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Delta Printer
Duet 0.8.5 firmware 1.19

I had a similar problem, the transistor for switching on the bed over heats and causes a short, so the green connecter melts.

I cool the replacement ramps board with two small fans blowing on the stepper drivers and switching transistors, and now the heat bed transistor only has to switch current
to the external relay I now use so it is not under any strain.

I use a 40a automotive relay , so more than enough for the job.