Geeetech

Hello there! About 2-3 months back I changed out my Sanguinolo board for a GT2560. At first look everything worked as intended, but after starting a print I noticed the MOSFET for the heatbed get way too hot. Even poking it for 1/10th a seacond and it will burn you. On my sanguinolo board I had an extra fan mounted above the MOSFET and it would never get to the point I could put my finger on it. The GT2560 got the same fan mounted, aswell as a heatsink which the sanguinolo did not have.

I have been searching for a while and have checked that the heatsink is not shorted, nor the connections for the MOSFET. The cables are connected safely, and no shorts there either.

Here is a picture of the MOSFET(The heatsink is screwed off it for testing purposes):
http://i.imgur.com/TiAjE8r.jpg

Could a solution be to take the MOSFET from the sanguinolo board and solder it on to the GT2560 board?

Do you test the voltage of the MOSFET, unstable voltage contribute mainly to overheating.

On the heatbed connection port or on the legs of the MOSFET itself?

I have checked at the connection port, which was steady at 12v.

Edit: Checked the voltage again, and now it started out at 9,5V and slowly built up to 10.70V ish when it was heated up.

Another thing to mention is that im only running the heatbed at 60C as I recently switched to PLA. There is no way you will be able to hold your finger on the mosfet, even within the first 10 seconds of powering on the heatbed. With the old sanguinolo board I used to have a temp of between 100-110C without the MOSFET getting warmer than 20-30C.

I have probably realized your issue, and there is a post about how to fix the max temperature error may be help you.
http://www.geeetech.com/forum/viewtopic ... 23&t=17030

What? Im not getting any errors, my printer is working fine. Im just worried as the MOSFET for the heatbed is running way too hot, and im trying to find a solution to get it cooler.

Have you solved this issue? Is it an issue? I am also worried/ thinking of buying another separate mosfet?

Mine is also getting very very hot(can’t hold my finger on it not even 1sec) but everything is working fine. Printing great.
Hotbed is warming and keeping the temperature 60° for PLA.
Is this a power issue from the PowerSupply a GT2560-A+ board issue(mosfet defective?) or a HotBed issue?
I’ve measured 12.6V directly on the power supply when nothing connected.
When I connect to the board the FANs receive 11.0V
Resistance of the heatbed is 1.7Ohm

What can I further check?
I think it is not normal that the MOSFET is getting so hot.
Has anybody found a solution?
Thanks in advance.

Maybe you can swap the extruder and heat bed wiring then you can determine if it is a MOSFET problem

The mosfet is probably very hot because the big current, or the unstable Power supply. I didn’t figured it out. I am using without the heated bed as I am
using only PLA. I am thinking adding a better quality Mosfet, or a bigger Power supply, as the 15A power supply that came in the Kit it is on it limits. It can draw a maximum of 180W(15A*12V) as for my whole setup with part cooling Fan and everything is drawing at maximum load of approx. 178W. So on it’s limits. The Voltage drops under 10.2V when everything is on( heated bed, motors, hotend, fans, mainboard).
I also read that the Mosfets used in the GT2560 A+ are not the best ones for such a big current. So I am thinking of buying an extra mosfet board, something like this:
http://s.aliexpress.com/uuyuQBny.
It is a try worth for the couple of Euro-s.

The MOSfet on mainboard GT2560A+ is STP55NF06