How to Wire an External MOSFET on a Mini 5 Plus

random_task_1

I purchase the mini 5 plus to replace a fried skr board in my printer. The heat bed is a MK2 PCB style 300x300 bed. The bed says it is a 400W/18A bed so the specs on the Mini 5 say it will not drive the bed direct from the board.

I already have a mosfet installed in the printer with power wires directly from the PSU to the mosfet and power wires from the mosfet out to the bed.

I am unclear where to plug in the signal cable (small gauge (20 or 22) 2 pin JST) from the mosfet and the proper wiring for the duet mini 5 plus.

I am also open to other suggestions on the best way to wire up the bed.

I am new to the duet community and I spent a good bit of time searching for this answer on this forum but did not find one, so if this is a repeat feel free to point me in the right direction

Thanks

jay_s_uk

@random_task_1 you could driver the bed mosfet from the bed heater outputs (don't forget to wire power to the bed inputs), the second heater output or a fan output

random_task_1

@jay_s_uk
Ok, thanks for the reply.
Just to make sure I understand what you said there.
I would put a + and - wire from my PSU to the Duet Mini 5 Power In terminals.
Run a + and a - wire from the Duet Mini 5 BED OUT (OUT_0) to the + and - INPUT side of the MOSFET.
Run a + and - from the MOSFET BED OUT to the normal input on the heated bed.
Run the JST 2 wire connector from the Duet Mini 5 OUT 1 terminal to the MOSFET Signal connector.

jay_s_uk

@random_task_1 power in to duet mini for the bed power input.
The 2 wire JST would go from bed out to the MOSFET.

random_task_1

@jay_s_uk
ok,
I think I understand now thank you. will give that a try when I get back to the shop

random_task_1

@jay_s_uk
just to make sure I understand correctly, you are saying it is fine to use the 20 or 22 gauge wire and run from the bed outputs on the duet to the signal input on my mosfet? I have it connected that way but want to make sure I'm not about to fry something.

fcwilt

@random_task_1

I suggest you purchase a suitably rated SSR (solid state relay) . They are designed for this sort of thing are are going to be safer than just a simple MOSFET.

Frederick

random_task_1

@fcwilt I'm not opposed to getting an SSR, any suggestions on which one to get? the Duet documents list two options but none are available any longer.

jay_s_uk

@random_task_1 large MOSFETs are fine.
Wire it like this

Just use out0 in place of where it wires to the ramps board. Make sure you provide 24v power to the power inputs for out0

random_task_1

@jay_s_uk ok, thank you for that clarification.

fcwilt

@jay_s_uk

IF they are optically isolated.

I would still suggest a SSR as nothing is exposed.

Amazon has these in stock:

Crydom D2425 SSR, Panel Mount, 280Vac, 32Vdc, 25A

Frederick

Dad003

just be aware that some of these mossfet get really hot , i went throw a few of these before , hard to get a quality one , now i just use fast switching SSR . and it solved my problem .