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Author Topic: Multiple PSUs and Grounding  (Read 13277 times)
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May 04, 2013, 03:56:21 PM

There is ONLY one potential issue, with relation to "plug-neutral"...

This "situation" only exists if you have one PSU plugged-in to one half of the circuit-hot-A, and the other PSU plugged-in to the other half of the circuit-hot-B. The circuit I am talking about is the two circuits which US power is split into. Usually, each room has multiple plugs, but all are either on circuit-half-A or B, not both in one room. However, if you had an "extra" leg of power added to a room, and that leg is the opposite half of the hot-circuit... and you plug one into one, and one into the other, and attempt to join them... there is a 50% chance that the unrectified connection will share a 220-240v potential between the PSU's, through the hot-legs. Since the "common" is grounded to "neutral", which is shared for both, since they are both mounted in the same case, and grounds for 12v are shared "dc common", throughout the motherboard.

This is NOT an issue if you are using one power-strip for both PSU's. But I imagine someone my hijack an additional outlet, for use in bitcoin mining, after having a second-leg circuit installed into a new room, along side of other equipment.

You can join any grounds, since they are all already joined by the case, the MOBO, and every other component. It is "better" to have the cases themselves grounded, as that stops the "noise" from traveling through the ground-plane in the MOBO, where the cases are not joined/grounded. If they were isolated, the cards would not function. Only optoisolators could be used to separate the two sources, which is NOT how any computer components function. (Only old parallel ports did that, where voltage-potential "leaking back in" would destroy the sensitive LPT chips.)

Voltage will never "FLOW" back from one PSU, into another, due to all the circuit designs which protect against that. You will simply get the average voltage potential out, and the combined amps out, for that average voltage.

12V + 10V = 11V out (On a starved PSU that is outputting 10V for whatever reason.) The combined amps would be 10A and 8A = 18A @ 11V. Thus, more stable than one PSU, which would be that one starved at 10V, which would drive-up the amps, and further kill the PSU or attached component. 2V will not be "flowing in" to the other PSU, unless there was no load attached, and unless the circuits had reached the reverse-voltage break-down limit, which would not happen with 10V on the other side and 2V "trying" to potential-in.

This is NOT against ATX V1, or V2 specs... this IS ATX specs. It is called tandem and redundant operation supplies of external sources.
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May 05, 2013, 07:40:05 AM

ISAWHIM -Just to expand a bit, first a clarification - A and B are phases, not circuits. Phases represent the different angles that AC electricity is generated. Circuits refer to wiring segments with some kind of Over Current Protection like a breaker.  Otherwise you're explanation is correct.

 I'm only clarifying because as I understand it, you can connect different phase neutrals together but you're not supposed to connect different circuit neutrals if on the same phase.  In case anyone is wondering, flipping a breaker and checking what is off and on only indicates what is part of the same circuit, it tells nothing about the phases, which you would need a meter like a multimeter to check.  As you said most receptacles will be on the same circuit which means the same phase but on the off chance you have receptacles on different circuits (different breakers) there are 2 possible situations, neither of which are good.  One is the same phase thing I mentioned which is not good for the AC neutrals, the other is multiple phases where you now have a 220-240v potential between the AC hots as ISAWHIM indicated. Anyway that's where my knowledge stops!

As for the link, somewhere in there the author talks about the "grounding" within power supplies and what needs to be done in order to run them together although I don't remember what exactly was said, something about isolating the internals of the PSU from the PSU case.  Hope it helps.
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