Hi

Keep in mind that there are a whole bunch of different thermistor types made. In general they are not interchangeable. You will need to match whatever thermistor is in (or on) the silicone bed to your firmware in order to get things to work.

Another basic issue: The FET on the Ramps is only good to 11A. If you are running 12V, that is a 120W power level. It does not matter what sort of heater you put on there. With 12V, 120W is the best you can do. If you put a 600W heater on there (with a 12V supply), all that will happen is that the thermal fuse will cut out and you will get a "heating error". The answer to that one is to run a higher voltage (which has it's own issues) or to run an outboard solid state relay.

Bob