Electrical question regarding PS_ON.

  • I'm currently reworking my printer (Anet A6) which is currently pretty much stock (except its running on Duet WiFi and all new wiring). It will be converted to an aluminum frame and some other stuff (Titan aero, bl touch, independend Z motors and endstops ...) soon.
    Now I'm thinking about doing a setup like this:
    Meanwell RD-35A (https://www.meanwell.com/webapp/product/search.aspx?prod=RD-35) to supply 5V to Duet Wifi (and 12V to 2 Fans and a Finder contactor).
    Finder Contactor (https://gfinder.findernet.com/public/attachments/22/EN/S2221_22_23_24EN.pdf oopsie did insert a wrong link...
    https://gfinder.findernet.com/public/attachments/22/EN/S22EN.pdf) to route power to a second powersupply.
    2nd PSU Meanwell RSP-320-12 (https://www.meanwell.com/webapp/product/search.aspx?prod=RSP-320) to power the rest of the printer (stock Anet heated bed and motors, hotend replaced by 30W E3D heater).

    My question is:
    When I supply 12V from the RD-35A to the finder contactor and then connect that to the Duet's PS_ON port can it handle the 12V and "high" current needed to engage the Finder contactor?

    If needed I can try to draw up a wiring diagram.
    Any feedback is appreciated.

  • Is there a reason for you to use the Finder Contactor instead of simply a relay module (which can be bought for a very low price)?
    It may help if you can provide a diagram of what you are planning. I see that both PSUs are 12V (the one being the stronger one) - is the idea to have both connected to Vin, or how do you plan to power the Duet? Using a stepdown buck regulator to 5V is a good option (but adds yet another component).

    On my setup, I have a 24V relay module with the relay coil between my power supply and the PS_ON and have not had any issues (running like this for more than a year now).

    With relays, the higher the voltage rating, the lower the required current to keep the relay triggered. For a typical 12V relay, one only need about 100mA (depending on exactly the model and other specifications).

    Looking at the Finder Contactor datasheet, it draws 2.2W, so for 12V that is below 200mA - the PS_ON can handle it. It also look like it have practically 2 relays inside - do you need 2?

  • Thanks for the answer Jacotheron.

    My reasoning behind the Finder:

    • Inrush current of the RSP-320 is about 40A (@230V)
    • I live in Germany and with our Plugs you never know which wire will be the phase -> disconnect both.

    Reason for 2 PSUs:
    The RD-35A supplies mainly 5V -> Power to the Duet. Added bonus it supplies 12V as well -> better for engaging Finder and operating an electronics cooling fan (maybe heatbreak cooling as well).
    RSP- 320 will supply the main 12V for heaters and motors -> duet can shut that one down if anything goes wrong.

    Will at a wireing diagram later today.

  • Ok, that makes sense. Here we have 3-prong plugs that should be wired in a way that 1 is always the Live.

    I missed the dual Voltage part of the datasheet for the small one.

    In this case it makes sense and should work.

  • Thanks again for the quick answer.
    Here is the wiring diagram (in case it can help someone else) with huge appologies for the quality. Just realized I did not have a propper program installed so I used paint...
    Keep in mind I'm not an electrical engeneer and have not tested this yet. Copy at your own risk.

  • @joshi Do you already have the power supplies? If you don't I can suggest an alternative design.

  • @insertnamehere No, I was going to order this weekend. Please share your suggestion.

  • @joshi
    Another possible solution is to use something like the fanless MeanWell HLG-600H-12A
    A 12V supply that has a 5V standby built in and a remote on/off. If you invert the PS_ON signal the Duet can control the 12V directly without high current relays.

    Something worth considering at this point is going to 24V. Steppers run faster and quieter and with a 24V heat bed, faster heat up times and higher temperature.

  • EDIT: I might consider using that contactor to have an interlocked control for heated bed with a thermal cutout switch instead.

    Have you considered and ATX power supply instead?

    ATX PSU will give you +5VFSB that is always on, then you can bring the PSU out of sleep mode with the PS_ON wire.

    I am currently building mine up this way using a different set of hardware but the concepts are the same.

    The ATX_PSU control concepts are covered here-



    look at how the PS_ON control is using a couple of resistors and MOSFET to control the PS_ON_IN wire, or how it controls the FAN wirings.

  • @insertnamehere :
    Meanwell HLG-600H : quite interesting that those have contacts to be switched on and off... but having had a look at the price tag ... I guess if I spend that amount of money I would still go with two PSUs but have the high get a high powered one from Puls they offer some with way lower inrush currents -> easyer to find something can handle the current.
    24V ... was thinking that at some point as well... might well end up using my old PSU a little longer and when the new frame is strong enough to handle all the motors can give at 12V then switch to 24V (which would then neccesitate a new heated bed and so on...)

    @sinned6915 :
    ATX PSUs are nice and tough things. But they have way to many small wires bringing out 12V which would have to be replaced with a few stronger ones... Also nowadays you need to make sure they do not have individual 12V circuit build in (or that you can at least connect these circuites i.e. BeQuiet (ATX PSU manufacturer) calls this combining OC mode if I remember correctly). The link to the Duet schematics is very interesting... The search for a data sheed of the mosfet used for PS_ON did bring up this document: https://assets.nexperia.com/documents/data-sheet/PMV40UN2.pdf . It states "Enhanced power dissipation capability of 1000 mW" -> the 2.2W the Finder needs will become a problem here...

  • administrators

    @joshi said in Electrical question regarding PS_ON.:

    The search for a data sheed of the mosfet used for PS_ON did bring up this document: https://assets.nexperia.com/documents/data-sheet/PMV40UN2.pdf . It states "Enhanced power dissipation capability of 1000 mW" -> the 2.2W the Finder needs will become a problem here...

    Not so. A MOSFET can switch much more power than it can dissipate. For example, the Duet fan mosfets can safely switch a 1A 12V load, which is 12W.

  • @dc42 right... note to self sunday morning 3am after a couple of beers is not the time to think tech...

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