Step down buck converter for heatbed wiring question

  • I want to get another Duet 2 Maestro for my Prusa i3 MK2.5S, but I want to run a 24V PSU to power everything. I already have another E3D v6 with 24V cartridge, so I'm not worried about that, but I don't want to replace my 12V heatbed.

    If my heatbed is 150W, at 12V it will be pulling 12.5A. I'm thinking about getting this step down buck converter to power the bed. I have an extra DC DC SSR (even though it's the one that the wiki said not to get ...didn't read it until after I bought it) that I can use to wire it to the Duet 2 Maestro for it to control.

    In the Q&A section of that Amazon link there is this:

    Question: Anyone mesured the 20a version to see how much current backfeeds into the output when the input is removed??
    Answer: yes there is im not sure how much but i know there is youll need to connect a 20 amp schottky diode on the out put side to stop that problem.

    I know some about electronics but not enough for this. I'm not exactly sure what they are saying. I'm not sure if they saying that when you turn off the current going to the converter that it still has some power that's going to the load connected to the converter (in this case, heatbed), or if there is power back feeding into the the source (in my case, the 24V PSU.)

    What would be the correct way to wire this up, or is there another suggestion?

    I suppose I could put the SSR between the step down buck converter and the heatbed, or I can put it between the 24V PSU and the buck converter (which I think might be the dumb thing to do.)

    The second question I have, will the SSR get hot from being used in this manner?

  • @ringo1508 You connect the convertor to the power supply. The positive to the output side, and the negative drrectly to the bed. The ssr will control the positive going to the bed. Connect the ssr input to the bed connector on the duet. Pay attention to the polarity on the ssr. If the ssr is one of the crappy ones, you won't get the full 12vdc to the bed and run hot.

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