Ramps Vs. Melzi Boards

[brainscan]

I would just like to say to anyone about to buy or build RAMPS 1.3/1.4 that the MOSFET for the heated bed has been poorly chosen. Best thing you can do is drop one of these in it's place IRLB3813PBF MOSFET, N CH, 30V, 190A, TO220. If you plan to have a heated bed you should definitely do this or have a serious heatsink and fan. Even with decent cooling the standard one will fail quickly due to heat stress. The replacement barely gets warm with or without a heatsink.

[Roxy]

I would just like to say to anyone about to buy or build RAMPS 1.3/1.4 that the MOSFET for the heated bed has been poorly chosen. Best thing you can do is drop one of these in it's place IRLB3813PBF MOSFET, N CH, 30V, 190A, TO220. If you plan to have a heated bed you should definitely do this or have a serious heatsink and fan. Even with decent cooling the standard one will fail quickly due to hear stress. The replacement barely gets warm with or without a heatsink.

Another answer is to just use the MOSFET on the board to drive the coil of a relay. The relay won't take much current from the board, and can be switched on and off to keep the temperature where ever it needs to be.