Mosfet Burn

hi my ramps 1.4 have a mosfet burn (heatbead) but in my city is hard to find electronic parts i dont know much about electronics so i want to ask if this mosfet can be use insted of the stock of ramps


Stock IRF512

4.9A, and 5.6A, 80V and 100V, 0.54 and 0.74 Ohm

Replacement IRF640

N - CHANNEL 200V - 0.150Ω - 18A

Thanks in advance

How much current does your heatbed draw?

12V 10 amp the heatbed is mk2b

Ok then it's no suprise for me that the IRF512 damaged. You need a very big heatsink to handle 10A.

For the IRF640 you will need also a quite large heatsink: at least around 6K/W.

Try getting a Mosfet with a RDS(ON) smaller or equal than 0,018 like the STP55NF06 which is used in the most Ramps boards. This one should work, even without a heatsink. But you can add a small 27K/W one just to be safe.
An alternative Mosfet would be the IRL3803 with a RDS(ON) of 0.006.

Edited 1 time(s). Last edit at 05/27/2013 05:41PM by johni85.

ok thanks for the assintence i found this irf 3205with rdson .008 and work great in the hotend and the fan the but with the heatbed i have a problen as soon as i turn on the heatbed the power supply (power switching (led) 12v 30 A) shut down the power and when i disconnect and connect the power supply to restablish the power the mosfet is blowed i tried dierent mosfet like irf 3205, irfz44n, p60n06 with the same problem i dont know what could be

That looks lika a shortcut. What is the resistance of your heatbed? I had a similar problem with a new heatbed which has a too low resistance. But it only killed my mosfet. The power supply was strong enough. You can also try to connect for example a fan to the heatbed connector to test if somethimg is wrong with the Ramps board.

i put a heater cartridge and work without a problem dont kill the mosfet and the cartdige heat normal the resistance in the heatbead is 1.4ohms

also i connect the fan and work ok but as soon as i try withthe heatbed the problem appear again the power shut down and the mosfet blow

Found the problem and solved
The problem was the pcb Heatbed this has a short the solutions has changed the pcb heatbed