Mk2a Heating Bed Problem with Ramps 1.4

I've looked at the other threads and none of them seem to be describing my problem or maybe I don't know the correct search terms for my problem, either way here it is:

I have a Mk2a bed with a resistance of 1.2 Ohms.
I am using a ramps 1.4 board.

When the bed begins to heat up everything works well for a little while but then the heating light on the ramps board will go out and the bed will stop heating.
The voltage to the board starts around 12V and stays there but when the bed stops heating/the light goes out the voltage drops down to almost nothing.
I have noticed the larger yellow fin (which I believe is some sort of self regulated fuse from reading posts) gets very hot. If I let it cool and attach the bed again it will work but then when the fin heats up again the power to the bed drops again.

What is causing this issue?

Thanks in advance for your responses. I will try to answer questions as promptly as possible.

Hi,
it es the PTC-Fuse. Its resistant raises by temperature (positive temperature Coefficient). I also had problems withe the high current of my heated Bed. If you don´t want to use a relays as I do, you will have to cool your Fuse! With a relay everything stays col (you should cool your stepper drivers...)

Manu

Yes, just fit a small fan directed at the fuses - you should have no problem after.

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Waitaki 3D Printer

Also, you should put a heatsink on your FET driver with high current bed. Mine got hot enough to burn the header next to it. You will want a fan on the board without exception.

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"Never argue with stupid people, they will drag you down to their level and then beat you with experience."

It happened to me to, it was wrong wiring, I printed enclosure and when i was rewiring I mixed one leg of heatbed D8 and other leg of fan D9. So in short just recheck your wiring.