Hello all!

This is my first post, and I'm really happy to have found this forum, as it looks like a huge wealth of knowledge. I'm hoping you 3d veterans can share some wisdom with me.

I have a Megatronics V2 (upgrading to a Smoothieboard 5x in the near future). To date, I've only printed in PLA and TPE, but I'm ready to get into some more demanding materials. So, I picked up a silicone heater for my print bed, which is a 365mm diameter 5/8" aluminum plate. I built my printer as a spinoff of the mini Kossel, but it's quite a bit larger than the standard, hence the large plate. The heater itself is 300mm diameter, 12v, 300w. And that is where things get sketchy for me.

I've dug around my controller and its schematics and found a bunch of different (somewhat contradictory) information.
  • The schematic states that the HB input runs through a 25A fuse, however the board appears to have a 12A fuse on the HB circuit.
  • According to the pcb schematic, the HB connector is rated to 18A.
  • The HB MOSFET datasheet rates it at 60v, 62a, with 135w of power dissipation
  • The Megatronics datasheet rates the HB circuit for 15A at 12V.


Now, I understand that the 300w demand of the HB is going to exceed pretty much all of the specs for the board and its components. Therefore, what I'd like to know is can I somehow pull that power down to within a tolerable range without making any major modifications? I'd prefer not to use any external controllers if possible. My soldering skills are decent, but I would prefer not to modify the board itself to drastically. My calculations pit the resistance of the HB at 0.48Ω. If I wanted to get the amperage down to 15A (the alleged rating of the board), I'd need closer to 0.8Ω. If someone smarter than me can confirm that, how could I even attempt such a thing?

The second part, relating back to the info I found is: what is the actual limit of the board? If there's actually a 12A fuse in place, I'm assuming that's going to govern everything. But with the board datasheet claiming 15A, am I to trust it?

I appreciate any input as I'm just standing by until I know I won't start my gear on fire.