MK3 Aluminum burning MOSFET?

Hello Reprap community.

I own a cheapo CTC Prusia i3 B (the plywood one) and two days ago I changed the standard MK2 heatbed with a MK3 Aluminum. Soldered the wires and connected them so it works on 12v, everything worked fine and at one moment I noticed that the LED for the heatbed on the GT2560 isn't working anymore and the wires are extremely hot. I took everything apart, resoldered the wires to have much better contact and replaced the board (had a spare one). Yesterday it operated normally and the wires were just a bit warm, not much more than the MK2 heatbed, but it was also heating quite slow took about 10-15 minutes to reach 100C. Today I come home and turn on the printer, started preheat and noticed that the heatbed isn't heating, looked at the board and the LED is out again. My presumption is that the mosfet burnt out and I wish to know why? Did I have to make some adjustment while switching from MK2 to MK3 in terms of software or where did I go wrong?

The new heatbed is probably lower resistance than you old one and there for is puling more amps.
If the bed resistance is 1.3 Ohms then 12v / 1.3 ohms = 9.2A
On the RAMPs board the MOSFET for the heatbed is usually a STP55NF06L which doesn't handle the load very well.
On the China make RAMPs I change it out for a IRLB8743PBF.

I have also bought RAMPs board from staticboards and they are way better quality and don't have the MOSFET issue.

Steve

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My updated Instructable on our Prusa i3 Build
[www.instructables.com]

Hello
I all ramps 1.4 or MKS GEN you mount to use a relay impriomante is quite cheap in our country [reprapmania.ro]
But I mounted him escape the stress that can burn MOSFET

Check out the 5V regulator of the Arduino. If it only delivers 4.7V the P55-Mosfet won't switch fully open and heat up very fast. Using a MOSFet with 3.3V U_GS like the above mentioned IRLB8743PBF will eliminate this problem.