Second is the actually amperage that your PSU can deliver. Many RAMPS clones use MOSFETs that are not rated for 11A or even the average 8A you will see on a 12V heatbed. If you get a heater that draws more power it will kill your MOSFETs. Your theoretical limit is 11A at 120V, which is about 120W that a heater can consume. The first consideration is the MOSFETs of your board. There are many factors when considering if a heatbed will work with your RAMPS board or if your heatbed will destroy your board. This board is mainly a 12V board, but could be modified to work at 24V. This does add another set of steps to the assembly process, but we stuck with larger sizes to make it fairly painless. This provided more space for more passive components, as well as headers. In RAMPS 1.4 the capacitors and resistors are now surface mount (SMD) components. 6 Hacking (archived information and notes).

5.3.1 Other production boards found in the wild.5.1 The Heat Bed Mosfet gets TOO HOT!!!.2.7.2 Power Supply, Details and Considerations.2.7.1.1 Power for the Arduino Mega board.

Download 4 pin fan pinout