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AC/DC Converter and Grounding

  1. Apr 21, 2015 #1
    Hello everyone,

    So some background on what I am doing. We have a pelican case with a bunch of PCBs that require DC voltage. I have purchased these power supplies (http://www.meanwell.com/search/EPS-65/EPS-65-spec.pdf [Broken]) to do the AC to DC conversion. They are located inside the Pelican case as well. On the input side of this power supply they only have connections for the Live and Neutral AC line.

    The block diagram in the datasheet shows the Live and Neutral being inputted and the Ground connecting somewhere else, I'm assuming to a frame or chassis. This Pelican case has an aluminum top plate that has the lamacoids to control the functions of the various PCBs.

    Is it safe to put the AC ground to the aluminum top-plate?

    I'm thinking it is not since that is where they will have their hands and if a fault does happen it may give them a shock.

    I've done some searching around and I guess some AC/DC converters will tie the Ground to the V- on the output side. If I do this, am I bypassing the transformers function inside the power supply?

    Would it be better to tie the AC ground to the plastic Pelican case?

    Any insights into this would be very much appreciated!
     
    Last edited by a moderator: May 7, 2017
  2. jcsd
  3. Apr 21, 2015 #2

    tech99

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    Gold Member

    The PSU looks like Class 1 equipment, as it has a metal cover and requires a ground connection. If so, it will need a 3 wire AC supply: Live, Neutral and Earth (Ground). All exposed metal work in the equipment should be bonded to mains Earth. The completed equipment will need to be safely constructed from the AC mains point of view, because you have a number of PSUs in parallel which will require mains wiring, switching and fusing. You ask about connecting one side of the DC to earth. The transformer shown on the block diagram indicates a centre tap. If this is earthed, the PSU is giving + and - relative to earth and you cannot earth one side. It is probably best to have an electrician look at the AC side of the project just in case; if the unit was going on the market, it would need safety approvals.
     
    Last edited by a moderator: May 7, 2017
  4. Apr 21, 2015 #3

    berkeman

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    Staff: Mentor

    That's an open-frame switching power supply. As such, it needs to be mounted in an enclosure that is grounded, and you need to provide a fused power switch power entry module between the external power cord and the power connections to the power supply. The ground in the 3-prong power cord needs to connect to the metal of your enclosure using a bolt-down fixture (not a slip-on connection), and the fuse and switch have to be in the Hot lead.

    I agree that it would be best for you to have a qualified electrician or PE/EE help you with this. It's a bit too easy to mess up if you haven't done this before, and the results of a mess-up can be bad.

    Also, that supply needs air convection to stay cool. How are you planning on it getting convection while it's in the Pelican case?
     
    Last edited by a moderator: May 7, 2017
  5. Apr 21, 2015 #4
    The AC receptacle on the side plate of the Pelican case has a fuse embedded into it on the Live line which goes into the switch so that part I seem to have gotten correct. As it is right now, the ground is bonded to the top-plate. There is a side plate that is also metal, so from these replies, I should also attach the ground wire to the metal side plate. The rest of the case is plastic.

    As for the air convection, I'm working with a mechanical engineer (he actually has experience haha) and he did some stuff with vents and a fan, ran a bunch of fancy simulations and all that so should be good.
     
  6. Apr 21, 2015 #5

    berkeman

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    Staff: Mentor

    That sounds pretty good! :smile:
     
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