Topic: Multiple PSUs and Grounding (Read 14832 times)

http://www.procooling.com/index.php?func=articles&disp=52&pg=2

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.

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.

The GPU are only powered when the motherboard is powered on (among other things).

Just because a cable is connected doesn't mean power if flowing (think of light with a switch).

a mining rig not mining?  lol

rear view of a 1250 and a 650,  there is another 1250 in the lower rack, the 650 is powering one card on each rig  10x7970's

(see the paperclip?)
other pics at the photobucket

Most PSUs have an on/off switch, that overrides the paperclip. If not, you can always use an extension cable plug thingy (whatever you call that in english) with a switch.

I like the paperclip method but this makes the GPUs powered all the time.

What about when they are not mining and the rig is shutoff but the PSU still is feeding them power ( or maybe not ? ).

A dab of hot glue and that paper clip ain't going anywhere any time soon.

Just be sure to use a "thicker" paper clip and some electrical tape to hold it into place.  Kinda sucks when you come home from work only to find out that somehow (fan vibration?) the paper clip fell out on not one but 2 rigs.  

Nothing bad happened other than crashing and corrupting one of the usb drives but it kinda sucks to lose a day of mining that way.

Google is your friend

I'm linking to a Seasonic X-1050 review but it's built on the same platform as the X-1250. No minimum load required.
As to the AX1200, see the CrossLoad2 test results. Anything weird going on with 0 load at 3.3 and 5V? The answer is a resounding NO. You're good to go without messing around with resistors.

What happens if the paper clip falls out?

you guys are still over thinking this.

use a paperclip to short out the plug.  leave the psu on unless your moving cards around (or need it off for some other reason)

mine!

Yes.  Both of them are rail to rail designs.  I ran a similar (older version) of the X-1250 without anything but 12V PCIe connectors loaded for 6 months and it ran cool and quiet even at 900W+ load.

I have Corsair AX1200 and Seasonics ( X-1250 ) only so are they fine without that dummy load on the 5V rail then ?

Thanks !

Unless your PSU is an old group-regulated design, yup, that should be all you need.

Loading the 5V rails is a way to avoid what's called a cross-load, a situation where some rails aren't used at all and other are heavily loaded.
Group regulated PSUs could easily go out of spec - even dangerously so - in this scenario.

Keep in mind that if your PSU has a MINIMAL load defined for 3.3V or 5V, you should make sure that load is applied.
Otherwise you're running the PSU out of manufacturer's spec.

OK. Now I really am confused.

So basically all that is needed is just a mechanism of turning both PSU on at same time

Like this :

Artfortz claims there is no issue powering 1 GPU from multiple PSUs. Im not sure its something I would do if I could avoid it, but at least there is no such consensus.

First the reason for putting load on 5V rail had nothing to do with the 12V rail.

Older PSU (due to higher 3.3V and 5.0V requirements) converted 120V AC to 12V, 5V and 3.3V.  Not having a minimum load was bad to the method used in the AC to multiple DC conversions.

Today honestly there is no reason entire computer couldn't run only on 12VDC.  70%, 80%, sometimes 95%+ of the load is on the 12V rail.  To improve efficiency most modern PSU are rail to rail conversion.  The PSU converts 120VAC to ONLY 12VDC.  Then based on load converts some of the power on the 12VDC -> 3.3V DC and/or 5 VDC.  There is no reason to put any load any of the rails.  

So the general consensus is that :

-no need for common ground as they have common ground from the power strip anyway

-do not mix and match cables into one card ( e.g. do not have one GPU powered by 2 PSUs and just stick to GPUs powered by individial PSUs )

-still need a 5V load in order to put less pressure on the 12V line ?

Thanks and can someone confirm I got it right ?

I have a couple of rigs running since september on 2 seasonic 750's  4x5970.   KISS   just short the plug and use the pci cables, thats it.

If not then tell us how long they did last ...