Using 5VDC USB PSU to control AC mains power



  • The power supply I'm using for my printer is a 24V that doesn't have any type of standby power or remote switch capabilities. (There's a switch that's just wired between the A/C outlet and PSU VIN.) However, I'm thinking of using a USB power supply similar to those used for raspberry pi's to provide that standby power. In that case, I believe I can just plug the "wall wart" micro usb connector into the Duet, and I'll be good (for at least non-printing power.)

    My question is, how could I use that to turn on/off the primary 24V supply? I'm guessing some kind of relay that would turn on/off the A/C mains power to the 24V PSU would be needed and used with M80/M81 and the 5V, PS_ON, and GND pins documented here: https://duet3d.com/wiki/Power_wiring. My problem is that I don't know how to switch 120VAC with 5VDC only by grounding. The "arduino" howto's I've seen all have 3 pins on the 5VDC side of the relay (VIN, GND and Signal.) From what I've read of the duet wiki, I don't have a "signal", just a 5VDC and either a connected (power on) or disconnected (power off) ground.

    Or, perhaps I'm over-thinking this - and I just need to feed the constant 5VDC, constant GND, and attach the duet's "PS_ON" pin to the "Signal" pin of the relay?



  • Nevermind. For some reason, when I searched amazon for a solid state relay, the entire first page of results were only SSR mounted on logic boards (which require a high or low signal to activate the relay.) What I expected to find (and found after jumping a few pages into the search results) were SSR's themselves. You know, two contacts for a control (usually 5VDC) and 2 (or 3 if it supports both NO and NC) for the load (120VAC in my case)

    I also found something called a "Thyristor" that I've never heard of before. I guess I'm a bit behind on my basic electronics.



  • In my opinion the best solution would be PSU with PS_ON (I'm looking for something like that, but I've only found 250EUR Cosel unit 😞 ).
    Second best is to use classic relay switch as they are more reliable and cheaper than SSR.

    SSR would be best for controlling mains powered heater. This solution saves money on buying expensive high power PSU. I'd also reccomend to back it up with classic SSR for cutting of power in case SSR fails.
    All the above will be my setup.


  • administrators

    @garyd9 said in Using 5VDC USB PSU to control AC mains power:

    Nevermind. For some reason, when I searched amazon for a solid state relay, the entire first page of results were only SSR mounted on logic boards (which require a high or low signal to activate the relay.) What I expected to find (and found after jumping a few pages into the search results) were SSR's themselves. You know, two contacts for a control (usually 5VDC) and 2 (or 3 if it supports both NO and NC) for the load (120VAC in my case)

    I also found something called a "Thyristor" that I've never heard of before. I guess I'm a bit behind on my basic electronics.

    You can use a DC-AC SSR such as SSR-25DA.



  • Wow... this thread came back from the grave.

    I long ago wired a 25A DC->AC SSR to handle this and it works fine. (A traditional relay, not a board with a relay and all kinds of logic for high/low/etc.) I don't remember off the top of my head where I'm getting the 5VDC from the duet board (so PS_ON can ground it.) It's from one of the three jumpers near "INT 5V EN" and I found it gave a reliable 5VDC when the PSU was off. (I didn't want to tie up the 5V pin on the expansion header, and there have been reports of some SSR's not working well with only 3.3VDC.)

    In retrospect, being the printer doesn't rapidly turn on/off, I probably should have used a simple mechanical relay instead of a solid state, but the SSR was easier for me to find and the cost wasn't really a big factor.

    Take care
    Gary


 

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