The ATX process from start to finish

deltwalrus

I’m going to ask questions and make statements that probably seem very basic, but my current (heh) understanding of electric circuitry is also very basic. And rather than risk injury/fire/death, I would rather risk embarrassing myself by asking some simple questions.

My goal is to replace the stock power supply unit on my Anycubic Kossel Linear Plus with an ATX PSU. Both are 12V power supplies, so no change there. I’m hoping the ATX supply will be quieter (secondary goal), but I primarily want to be able to have the Duet board always-on with the ability to switch main power on and off via M80/M81 in G-code at the start and end of each print.

I have a spare ATX power supply (CoolerMaster RS-500-PCAR-A3) that says it delivers 18A each on the two +12V output rails it has. It also has a +5V standby rail that delivers 2.5A. Being an ATX supply, it also has the all-important PS_ON wire. I’m using a Duet Wifi board, version 1.04 I believe.

What I’m struggling with is exactly how to wire up the PSU to the Duet. My understanding (here is where I would love more input) is that I would need to:

"Short" the PS_ON (green) with any available ground connection (black) in order to allow the unit to soft-power on and deliver the 5V needed to always keep the Duet on… I’ve seen this done with a paper clip directly into the ATX harness (which seems dangerous) or with a resistor (which seems much safer). I assume I can cut and strip wires, twist onto a resistor’s leads, then heat-shrink those two nicely together.
Use a single +12V yellow wire from the PSU for the Duet’s "power in" VIN terminal (ideally crimped into a provided ferrule)
Use a single GND black wire from the PSU for the Duet’s "power in" GND terminal (again, ideally crimped into a provided ferrule)
Remove the jumper pin from "INT 5V EN" and move it to "EXT 5V EN"

Assuming the above is all correct, my questions are:

Is that truly all there is to it?
I saw an article that said "47R 1/4w resistor," I assume that means 47-Ohm 0.25W?
What about the +5VSB purple wire? Do I need to do anything with that? Add it to the VIN for the Duet?

When this is all done, I plan to take lots of pictures and put some sort of instructional blog post together, for folks like me who know enough to be dangerous, but need a little help to not burn the house down (like Danal did for upgrading to the Duet in the first place).

Power supply:

Thanks!

@deltwalrus said in The ATX process from start to finish:

"Short" the PS_ON (green) with any available ground connection (black) in order to allow the unit to soft-power on and deliver the 5V needed to always keep the Duet on… I’ve seen this done with a paper clip directly into the ATX harness (which seems dangerous) or with a resistor (which seems much safer). I assume I can cut and strip wires, twist onto a resistor’s leads, then heat-shrink those two nicely together.

no this is to turn on the full supply, handled by the ps_on connection. you should get 5v standby by just plugging in and switching the thing on.

@deltwalrus said in The ATX process from start to finish:

What about the +5VSB purple wire? Do I need to do anything with that? Add it to the VIN for the Duet?

do not add it to VIN you'll short it to 12v when psu turns on. feed 5v to the 5v_ext header and adjust jumpers as needed for your board.

deltwalrus

@bearer Okay, now I see the EXT 5V header. So I would build a 3-pin connection with the purple +5VSB wire going to the +5V pin, the green PS_ON wire going to the PS_ON pin, and any black GND wire going to the GND pin. Sound right? Or is that +5V pin supposed to get a regular +5V (red) wire?

Sounds like there's no need for that resistor at all other than testing purposes.

deltwalrus

Okay, so it looks like I need a few connections:

Use a single (or two?) +12V yellow wire from the PSU for the Duet’s "power in" VIN terminal (ideally crimped into a provided ferrule)
Use a single (or two?) GND black wire from the PSU for the Duet’s "power in" GND terminal (again, ideally crimped into a provided ferrule)
Remove the jumper pin from "INT 5V EN" and move it to "EXT 5V EN"
Build a 3-pin connection with the purple +5VSB wire going to the +5V pin, the green PS_ON wire going to the PS_ON pin, and any black GND wire going to the GND pin, this would go to the EXT 5V connector

Does that sound right? And should I use one 12V connection or two? The original Anycubic power supply says it is 300W, and this ATX supply delivers 360W split across those two rails.

Sorry to be so obtuse, but I really want to make sure I get this right.

dc42

@deltwalrus said in The ATX process from start to finish:

Use a single (or two?) +12V yellow wire from the PSU for the Duet’s "power in" VIN terminal (ideally crimped into a provided ferrule)

You shouldn't connect two independent 12V outputs in parallel. Maybe you can use one of them for VIN power and the other for the bed heater positive supply.

Use a single (or two?) GND black wire from the PSU for the Duet’s "power in" GND terminal (again, ideally crimped into a provided ferrule)

As the ground wires are probably not very thick, suggest you use at least two.

Remove the jumper pin from "INT 5V EN" and move it to "EXT 5V EN"

Build a 3-pin connection with the purple +5VSB wire going to the +5V pin, the green PS_ON wire going to the PS_ON pin, and any black GND wire going to the GND pin, this would go to the EXT 5V connector

You can omit that ground wire.

deltwalrus

@dc42 and @bearer thank you for the information, I am going to put together a quick diagram of what I am doing for posterity and then have a go at it either today or tomorrow. I really appreciate how helpful you've been!

deltwalrus

Here's what I intend to do, this way it can server either as a visual guide for others (I'm a very visual person) in case of success, or as a warning of how not to do it if I let the smoke out.

Either extending or re-using wires, depending on lengths... not using the ATX connector, that's just there as a reference.

should work, what heated bed would you use?

deltwalrus

@bearer Nuts, good catch... that's an input, not an output. I probably need another +12V to that, don't I? It's rated 18A on the PSU, so it's likely less than that. So I'll edit my above post...

@deltwalrus said in The ATX process from start to finish:

that's an input, not an output.

no its an output, but my point was to find out if you need more yellow wires to carry the current or possibly even find the second 12v rail and wire that to the bed directly to spread the load

deltwalrus

@bearer Yeah, I just ran down and checked it, you're absolutely correct. The existing supply is 12V, 25A output (rated 300W), and it's sending all 25A to the main VIN. @dc42 advises against sending 18A + 18A in parallel to VIN, but if I wire +12V and GND from the ATX directly to the bed, will I still be able to control the temperature as I can now?

Again, I apologize if these are simplistic or foolish questions, but I'm still learning and am not keen to scorch the place.

@deltwalrus said in The ATX process from start to finish:

@dc42 advises against sending 18A + 18A in parallel to VIN

sort of; but sending 18a through at least two wires is different, both the yellow wires on the 24p connector are from the same 12v rail.

then you can take the two yellow wires from the 4p 12v connector and run them to the bed. (also take the two black wires together with the other two).

(of course if your total current draw is less then 18a you'll be fine with just using the two yellow wires from the 24p connectors)

deltwalrus

@bearer Updated my plan:

This does still allow temp control via the board, right? I may or may not, possibly, have accidentally wired 12V VIN directly to the board one time by accident, and wondered why the bed just got hotter and hotter whenever I turned the supply on...

And should I also take another +12V from the 24-pin and couple it with pin 10 (so splice together pins 10 and 11)?

only the yellow/12v straight to the bed.
black/common from the 4p connector to gnd on the duet
and black from the bed to bed- on the duet.

@deltwalrus said in The ATX process from start to finish:

And should I also take another +12V from the 24-pin and couple it with pin 10 (so splice together pins 10 and 11)?

It wouldn't hurt. It all depends a little on what current your bed will draw, it may be cleaner to use the 6p pci-e conector for everything. (it was 12v1 according to the manual, with only the 4p connector being 12v2)

deltwalrus

I fear I am confusing this badly, but here's my latest understanding:

move the black bed wire up to the from the Vin screw to the bed- screw.

(But again, if your total current is under 18a it may be better to use your initial plan.)

deltwalrus

Okay, I'm going to try this arrangement out tomorrow:

Total current delivered (again, according to the crappy power supply Anycubic provided) was 25A, now it will be 18A + 18A.

Thank you, SO MUCH, for your patience and your expertise. I will report back my results tomorrow on this. Hopefully I don't melt anything...

@deltwalrus said in The ATX process from start to finish:

Total current delivered

not quite the same as current used tbh. and you won't actually have 18a+18a. You'll have 360w/12v=30A divided into two 12v rails of 18A max each. so 18A + 12A or 15A + 15A f.ex.

anyways, drawing should be fine, with the caveat the wires are thick enough to carry the current.

deltwalrus

FYI, I have not yet gotten around to this, as I need to travel for work, but I hope to get it done when I return next weekend. I'm still scared of frying a rather expensive board, so if anyone else has experience doing this, I'm happy to hear any tips you have.

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