What is the safest way to wire two power supplies to power the Duet and a heatbed, including fuses and switches? Is an external MOSFET required on the bed?

I have a 24V coreXY printer with LEDs, a single hotend, and a 300mm bed. I noticed the fan for the 350W Meanwell PSU kicks on often and seems to struggle with bed temps over 100C. It looks like PSUs over 350W jump to the $100-150 range. Instead, I bought a second smaller 24V/150W to power the Duet, LEDs, motors, and hotend for $15.

Originally I was going to purchase an external MOSFET for the bed but I believe there is a way to directly connect the larger PSU ground to the Duet heatbed output ground, and the heat bed in between the Duet and PSU since I think the Duet does the PWM control on the positive heatbed positive output.

Also, I would like to use one switch to turn both PSUs on if possible. I don’t think it is safe to use one of the standard “plug, fuse, switch” combos most printers use since it would be one fuse for two PSUs. I believe the correct way would be to use a plug with a switch then make three Y cables with their own fuse to split the incoming power between the two PSUs.

I’d like to verify the correct wiring before making a house fire though are there any schematics available? Thanks!

I actually had this exact problem while using an E3D strong but compact motor (0.9 degree type). There are four pins, it turned out that I needed to switch pin 2 and 4 in order to make it work. You may need to switch pin 1 and 3 if it doesn’t work. I figured this out by using a multimeter to measure the Ohms between each pair of coils. If you have a pair, it will be around 3-8 ohms otherwise it will be infinity.

I also verified the Duet was OK by using a known good motor on that driver.