OCZ 900W modstream can't cope with 3x GPU?

[psilan]

Using: http://www.newegg.com/Product/Product.aspx?Item=N82E16817341009

5970
5870

Add a 5850 in windows okay for a few days, but if I muck around and make some changes to anything it just becomes unstable.
Add 5850 in BAMT and it just powers off constantly.

Anything else it could be? OCZ don't have the best rep...

I am about to get another 1 or 2 5970s and I would prefer to have all 3 on the same rig.

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[Coinoisseur]

Best guess is you are overdrawing on one or more of those multiple 12V rails.

[crazyates]

Best guess is you are overdrawing on one or more of those multiple 12V rails.

^^^

Those 3 GPUs shouldn't be using more than 500W, so you should prolly try switching around your load balancing.

[psilan]

Mmm ok cool, thanks guys. I will give that a try and update.

[psilan]

How would you balance this?

PSU
Hardwired;
- 8xPCIe
- 8xPCIe
- 6xPCIe

Modular (off HDD labeled area of PSU, no other way)
- 6xPCIe
- 6xPCIe
- 6xPCIe

I initially put 1 of each (hardwired & modular) to each GPU.
Tried 2x hardwired to 5970, rest random.

Not going to well for me here....

[psilan]

Just pulled out the 5850. Going nowhere .

[psilan]

Changed to 5870 5850 5830 and copes. Can't handle the 5970. Must be that great OCZ quality.

[squall1066]

I'd love to ba able to sugest something but i'm learning myself ATM.

It does sound like the board is not supplying enough watt's across the PCI-E, If you have 1x4 pin on the board, then this might not be enough, I have a rig with three cards and it uses 2x4 pin on the motherboard, another with two cards has 1x4 pin. (irrelivent of single/duel gpu card IMO)

I could be way off, I'm sure someone will point that out.

[psilan]

Thanks

Sorry I should have mentioned this is a MSI 890fxa-gd70
http://www.msi.com/product/mb/890FXA-GD70.html

Tried and true around here. I blame the PSU. Will find another and put this on my desktop .

[Ilikeham]

Each rail is low amperage, I think the PSU is actually out of spec to the card in fact.

[ajstar]

Single-rail PSU is the only way to go. Mine NZXT Hale90 850W http://www.newegg.com/Product/Product.aspx?Item=N82E16817116012 (on same mobo) handles 5970 + 2x5870 without problems.

[psilan]

Thanks for the advice. I have a single rail 850W corsair. I will chuck it on the system now .

[psilan]

Crazy, now running 5870,5850,5852,5830 off the single rail 850W...

Great tips guys, thanks.

[oldDirty]

few wekks ago i run 4 5850 on a Enermax Pro 87+ 600W, 1 AMD Quad, 4Gig, 2 HDD and 5 Fans without any trouble.

[AndrewBUD]

PSU's with single rails can handle the load when nothing else is being used.... depends on the PSU

[jermwerty]

Yeah that PSU has a bunch of 20A rails.  Most likely its something like Rail #1:  Motherboard, Rail #2 SATA/Molex, Rail #3 PCI-E, Rail #4 PCI-E

So the problem is because you only have three rails you can use to power the GPUs (assuming molex to PCI-E conversions) you can really only use three videocards!
 

Thats why I love my 5 cards on my single rail (76A) PC Power & Cooling 910W Silencer, draws 750W from the wall and is BAMT stable for months at a time!  I also used the same model PS with dual 5970s and it never broke a sweat pulling 620W from the wall.

I have a Rosewill 1KW that has the same issue as the OCZ, too many rails and I only throw two 6950s on it.  Sad 

[btcnut]

Put the high draw cards on the PCIe power rails, use the low draw cards on the molex rails and you might get away with it

alternatively, try undervolting one or more cards.

[The-Real-Link]

Good to hear it's fixed for you.  That original load balancing sounded pretty good so surprised it didn't cut it...

Then again I also avoid OCZ like the plague.  Sorry man.

[ARapalo]

I think modstream is not OCZ's high end series PSU. And also, if the motherboard doesn't have a dedicated 6-pin (or molex) power for the PCI-e, then you're drawing about 25w of power per GPU through the PCI-e lanes. This might cause some instabilities too.

[AndrewBUD]

I have a Antec 620watt High Current Gamer Modular power supply running 4 x 5850's without issue.... The PSU is hardly getting warm.....

Has been running fine for about 4 days now..... I was planning on putting two of them together but I tried 1 and it seems fine