MakerGear Forum

My 1st gen M2 keeps on burning up the MOFSET Heated Bed output on Rambo while keeping the heatbed at 110C for ABS. I've dealt with this issue three times in four years. So I installed an external MOFSET today in hoping it will save some headaches down in the line. But now the bed is not heating up at all, the extruder heats up fine. It was working OK before I installed the MOFSET. Please advise.

BTW, my 1st gen M2 came with a 12v 18a Dell PSU for powering heatbed.

External MOFSET https://goo.gl/VGuisY

My wiring diagram

javafuel wrote:It was working OK before I installed the MOFSET

The "Heated Bed" output gets power from the "A Heated Bed" input power terminals.

Connect a short wire from the +B terminal ("B Logic ...") to the +A terminal ("A Heated Bed") and It Will Just Work.

The PCB traces connect all the - terminals together, so you don't need another jumper.

For other folks discovering this thread in the future:

A DC-DC Solid State Relay will also work and may be somewhat less expensive. I wrote up some background and pointers:
https://softsolder.com/2013/09/25/impro ... -ssr-test/
https://softsolder.com/2014/06/05/maker ... oah-powah/



You must use a DC-DC SSR, not the more common DC-AC SSR.

The "Heated Bed" output gets power from the "A Heated Bed" input power terminals.

Connect a short wire from the +B terminal ("B Logic ...") to the +A terminal ("A Heated Bed") and It Will Just Work.

The PCB traces connect all the - terminals together, so you don't need another jumper.

Thank you the input. So I just need to power A terminal by connecting +B to +A? I thought the external MOSFET is already powering it through Rambo's Heated bed MOFSET output (blue wires in my wiring diagram).

javafuel wrote:connecting +B to +A

That'll do the trick.

The external MOSFET looks like it has an optically isolated gate through the little white IC: "Can use digital signal of 5-24v to control".

If that's the case, then the isolator must get that voltage from the Heated Bed connector, which means you must connect a power supply to the Heated Bed input.

Even though you're replacing the entire bed heater with an optical isolator LED, both need a power supply!

ednisley wrote:

javafuel wrote:connecting +B to +A

That'll do the trick.

It did the trick! Thank you very much.