Multiple PSUs and Grounding

[DBordello]

I have successfully gotten 6 cards working, on 3 500W PSUs.  I am no longer connecting their grounds (explicitly).  I appreciate the detailed discussion on this issue.  Hopefully everything remains stable. 

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[abracadabra]

I have successfully gotten 6 cards working, on 3 500W PSUs.  I am no longer connecting their grounds (explicitly).  I appreciate the detailed discussion on this issue.  Hopefully everything remains stable. 

Are you running anything on the 5V lines of the slave psus?

[bulanula]

I have successfully gotten 6 cards working, on 3 500W PSUs.  I am no longer connecting their grounds (explicitly).  I appreciate the detailed discussion on this issue.  Hopefully everything remains stable. 

Are you running anything on the 5V lines of the slave psus?

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

[jjiimm_64]

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.

[bulanula]

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 ?

[DeathAndTaxes]

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 ?

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.  

[P4man]

-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 )

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.

[bulanula]

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 :

[jake262144]

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.

[bulanula]

Unless your PSU is an old group-regulated design, yup.

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

Thanks !

[DeathAndTaxes]

Unless your PSU is an old group-regulated design, yup.

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

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.

[jjiimm_64]

Unless your PSU is an old group-regulated design, yup.

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

Thanks !

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!

[rjk]

Unless your PSU is an old group-regulated design, yup.

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

Thanks !

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!

What happens if the paper clip falls out? </troll>

[jake262144]

I have Corsair AX1200 and Seasonics ( X-1250 )...

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.

[DeathAndTaxes]

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)

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.

[jake262144]

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

[bulanula]

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 ? ).

[P4man]

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.

[jjiimm_64]

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 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

[DeathAndTaxes]

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 ? ).

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).