How to connect two Power supplies?

  • I had a RAMPS before, now upgrading to Duet WIFI.

    Before I used a 12V 10A supply (PSU-A) to power the extruder and steppers along with a second supply 12V 12.5A (PSU-B) for the heated bed.

    I'm now wondering how I can connect both supplies to the Duet WIFI?

  • You can tie the negatives of the power supplies and then disconnect the posative side of the heater from the duet and feed it direct from the power supply. Ensure the negative from the VIN to the power supplies is chunky emough for the peak expected load.

    Edit: This works because the heater are switched on the negative and fed with a permanent posative feed direct from the VIN connector.

  • Just to make things clear...

    PSU-A plus and minus to Duet input
    PSU-B minus to Duet input
    PSU-B Plus to bed heater
    Duet bed output Minus to bed heater

    Is that correct?

  • You could do it that way.

    Most PSUs have more than one pair of negative and posative terminals so I'd normally do [PSU A -] to [PSU B -] and then [PSU A -] & [PSU A +] to VIN on the Duet. [PSU B +] would feed the heater. Best to avoid crimping two wires into one connector if you can avoid it.

  • Ok, I finally got some time to give this a try. Just to be safe I created an image to verify the connections.

    My intent is to use two notebook powersupplies. Therefore I just have two bricks which don't have exposed 230V wires.

    Is this wiring correct?

    alt text

  • administrators

    No. The BedHeater- pin on the Duet should be connected to HeatedBed-, not to PSU ground. The BedHeater+ pin on the Duet should be left not connected.

  • @dc42 said in How to connect two Power supplies?:

    edHeater+ pin

    Just for basic electronic understanding, the heated bed has a voltage drop because of it's internal resistance like shown?

    Like so?

    alt text

  • administrators

    Yes, that's correct.

  • @adras Just to be nitpicking: in your diagram you wired the weaker 10A PSU to the bed instead of how you described it in your first post where the more powerful 12A PSU was powering the heater. Did you change that intentionally or did it just slip?

  • Yep, that's nitpicking 😛 I already got one PSU connected, so there's no way for me to do it wrong, because it's all about hooking up the remaining one. That's why I don't care about the numbers in the picture. The wiring is important.


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