Concept Is grounding DC in SFF PC required?

GDesign

Caliper Novice
Original poster
Aug 22, 2019
28
41
Hi all,
I'm hoping someone out there has the knowledge and/or experience to answer my query or at least point me in the direction of someone who can! I've tried looking into this using a website called 'Google' (if you haven't heard of it, it's a bit like AskJeeves, but will probably never catch on). The situation is this:

I am developing a SFF case made from stainless steel. The power will be delivered exclusively using a AC-DC power brick (e.g. Dell 330W) connected to a DC-ATX power converter (e.g. HDPLEX 200W, Minibox 160XT pico PSU). The input voltage will likely be either 12V or 19V. I am undertaking design risk management for the case with a consultant, and he has asked if I have considered grounding the case by connecting it to the earth circuit. I have not considered it and having no knowledge in this area, do not know a) if this is something I need to consider given the nature of the power input or b) how I would implement this in the design if it is necessary.

Is anyone able to advise? Probably unsurprisingly, the information acquired through my AskJeeves searches are either ambiguous, contradictory to other info or require a PhD in electrical engineering to understand! Any help gratefully received.

Graham
 

SFFMunkee

King of Cable Management
Jul 7, 2021
682
690
I'm no expert, but I don't think there's any need to connect the chassis to ground if it's only connected to an external AC/DC adapter.
However - if there is mains power going into the case (internal AC/DC or other PSU) then absolutely 100% you should be grounding the chassis to the earth wire/pin.

The benefit of grounding the chassis might mean that you don't get that slight electrical zap when handling multiple conductive devices at different floating voltages (e.g. when your laptop and phone are both charging and you touch both, little zap sensation), but again I'm not an expert so I'd wait for me to be corrected on this.
 
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GDesign

Caliper Novice
Original poster
Aug 22, 2019
28
41
Looks like ideally the chassis should still be connected to earth at 0V, but without the connection to the mains you won't have that so it'll usually use a reference ground from the AC/DC adapter?

Ground rules: earth, chassis, and signal ground (analogictips.com)
Hi SFFMunkee,
Thank you very much for taking the time out to reply - really appreciated! Thanks also for the useful link - it'll take me a few reads through to understand it, but it looks like it does a good job of describing the principles at play. From other resources, I get the impression that context is also important though, in terms of the voltage and currents involved in determining whether grounding is required (certain sources indicate that grounding would be required for higher [>50] DC voltages).

As the power supplied into the case I'm developing would be exclusively DC delivered via an external AC/DC (I can't type that without playing Thunderstruck in my head!) adapter, it sounds like this would have the ground covered. I have also contacted the team at HDPLEX on the matter who agree with this, so it's reassuring to have multiple opinions pointing in the same direction!

Thanks again!
 
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SFFMunkee

King of Cable Management
Jul 7, 2021
682
690
Hi SFFMunkee,
Thank you very much for taking the time out to reply - really appreciated! Thanks also for the useful link - it'll take me a few reads through to understand it, but it looks like it does a good job of describing the principles at play. From other resources, I get the impression that context is also important though, in terms of the voltage and currents involved in determining whether grounding is required (certain sources indicate that grounding would be required for higher [>50] DC voltages).

As the power supplied into the case I'm developing would be exclusively DC delivered via an external AC/DC (I can't type that without playing Thunderstruck in my head!) adapter, it sounds like this would have the ground covered. I have also contacted the team at HDPLEX on the matter who agree with this, so it's reassuring to have multiple opinions pointing in the same direction!

Thanks again!
Good one, make sure you post your build when complete, I'm sure I'm not the only one who'd love to see it :)
 
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