OCZ GameXStream 1010W rail configuration

[MrTeal]

http://www.hardocp.com/images/articles/11804833867kZOkB92i8_2_6.gif

Yes, I know it's kind of a POS, but the price was right. I'm not too worried since I expect the draw at the wall of the system to be in the 700W range, but I am wondering what is the best way to configure the system for mining.

It's a 4 rail supply, each rail rated at 20A with the max on all 4 rails being 75A.
12V1: EPS
12V2: PCIe0, 1
12V3: ATX24, Molex, Sata
12V4: PCIe2, 3

Since I want to run four cards, I'm a little worried about overloading the third 12V rail. The cards have molex to PCIe adapters, but four PCIe adapters plus the PCIe bus power and other MB draw is sure to overload the 240W capacity of that rail.

One option I thought I might do is splice a second PCIe connector onto each PCIe rail, running two cards off each PCIe rail. The 5850s won't be drawing more than about 150W, so as long as they draw at least 30W from the bus that should be safe.

The other option would be to add one PCIe connector to each of rails 2 and 4, and two to rail 1. The CPU will be underclocked and undervolted and will sit idle most of the time, so even if each PCIe connector on that rail pulls 75W (6.25A), that would still leave 90W max on the rail for the CPU. Seems like it should be ok.

Of the two options above, which seems like it would be the safest and most stable? I'm leaning towards the first, since while the second gives better margin I don't really want to deal with the random BSODs that come with CPU instability.

Does anyone know how much current the Sapphire 5850 Xtremes draw from the 6pin connectors vs the PCIe bus?

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[diabinc141]

Come on man, you gotta invest in a good power supply! Always single rail, and high quality. Then you never run into any problems. Also, DO NOT use pci-e adapters for long. In fact I tried adapters on one of my power supplies and it failed after an hour. You need to get a good PSU with enough connectors. However, very temporarily you should be fine but don't over clock at all and look for a new PSU.

The cards though should draw around 20-25 watts from the bus. As for total power usage and 6 pin power usage I'm not sure. There are plenty of 5850 power usage forums here though just look around. I would suggest you undervolt the cards (you'd be surprised how much less power they use) and underclock them until you can get a new PSU. This will insure no hiccups and more peace of mind.

And there should be no CPU instability because it shouldn't be used (unless you have the 100% usage bug). Just underclock that thing and go with option two and you'll be fine. Also what CPU do you have?

[jake262144]

Yes, I know it's kind of a POS, but the price was right.

Except it probably wasn't right. Crappy rail topology and connector count⁽¹⁾ basically make this PSU a three GPU capable device thus degrading it to a 650W level.
Is there any excuse for not fitting a 1kW unit with even one sodding PEG 8-pin connector???⁽²⁾

A decent 800W unit would have no problem with powering four 5850 cards which this PSU just can't do without some hardware hacks and thus voiding your warranty.

A 5850 is a 150W-ish card.  150W at 12V is 12.5A.
A PEG 6-pin connector is rated for 75W by the ATX spec.

Without soldering in additional connectors the best you can do is:

rail2 -> a single 5850 card
rail4 -> a single 5850 card
rail3 -> a single 5850 card using two double molex -> one PEG-6 connector adapters (be sure to have read this topic)

Each of those rails is only loaded in 62% but there are no wires to fit in a fourth card.

One option I thought I might do is splice a second PCIe connector onto each PCIe rail...

We're talking of a crappy PSU here - isn't it better to sell it off on e-bay and purchase something decent? Is it worth all the hassle?

If you choose to proceed with your wacky plan, your best bet would be to solder in one PEG-6 connector to rail2 and one to rail4 and run the fourth card off these:
rail2, rail4 -> a single 5850 card

Whether you do so by
(1) clipping off one PEG-6 connector and soldering/using wire nuts to attach two PEG-6 connectors in its place, or
(2) opening up the PSU and soldering in some additional wiring fitted with a PEG-6 connector (e.g. recycled from a dead PSU)
is of no great importance.

The first option is the quick-and-ugly but easy path. The second, while more labour intensive, is the elegant solution.
If you go with wire nuts, make sure to twist all those wire strands firmly together - the last thing you need is a short circuit taking out your cards.

Remember, however, that I take no responsibility for whatever damage or physical harm you might cause by messing with your PSU.
Whether it's you or your mining rig that gets zapped, whether your PSU, your house, or your neighborhood burns down, don't come crying here.

I'm not too worried since I expect the draw at the wall of the system to be in the 700W range, but I am wondering what is the best way to configure the system for mining.

Simply put, without voiding your warranty you can't. That's what you get for getting lured with the price.

Notes:
(1) :chuckles: It might only have four PEG-6 connectors but hey, it's got not one but two floppy connectors, fancy that!
     You can hook up two floppy drives and copy floppies in a most convenient fashion!  

(2) the only explanation I can come up with is that those 12V rails really can't deliver the promised 20A:
     A PEG-8 connector (rated for 150W) and a PEG-6 connector (75W) combined might require up to 225W (18.75A) from the rail.
     If the manufacturer didn't feel confident that their PSU was capable of actually delivering such loads, they would naturally go with two PEG-6 connectors.

[MrTeal]

So the cards really don't pull much power through the PCIe bus and most of it will come through the 6 pin connectors. I guess that removes the first option, I won't be able to run four 6pin connectors on each 12V rail if they're loaded down with 75W each. I can still add one additional PCI connector on each rail and still be under the 20 amp mark on each rail.

Looking at the actual topology of the supply, it is actually a single rail split four ways for overcurrent protection as opposed to four physically separate rails. I guess I'll have to take it to work and actually load down the rails to be sure, but if the supply does make 75A between all three rails I should be ok, at least stock or undervolted.

Just to be clear, I'm not going to use molex to PCIe adapters. I'm planning on soldering connectors onto the PSU. I might have to save up for a good 1000W supply eventually, but if I can make a $60 supply work for now I'm going to give it a shot. Thanks for the opinions guys.

[DeathAndTaxes]

I would second (third) the recommendation on not trying to jury rig the PSU.  Mining is very hard on PSU, far harder than just about any retail application including enthusiast gaming.

Mining could best be described as a PSU torture test.   Low end PSU are going to die and before they die they are going to choke having all kinds of ripple issues, and inconsistent power, bad regulation, and random OS crashes.  If spending lots of time trying to debug systems that can't be debugged because they have "random" power as an input sounds like fun then precede.

That PSU isn't 1000W BTW.  It is a "game" lower end PSU suppliers play.  See it is 1000W but we configure it so you could never draw 1000W thus it appeals to people who buy on specs.  Someone with a cross fire system doesn't need 1000W but 1000W sounds leet and this one is the cheapest so why not get 1000W instead of some "lame" 800W by a competitor like SeaSonic.

You soldering in new connectors likely will work assuming the PSU can actually handle the load.  Bad news is your likely won't know until you mod it.

To answer your question most cards draw about 20W to 40W from the PCIe bus.

[jake262144]

I would second (third) the recommendation on not trying to jury rig the PSU.  Mining is very hard on PSU, far harder than just about any retail application including enthusiast gaming.

Mining could best be described as a PSU torture test.   Low end PSU are going to die and before they die they are going to choke having all kinds of ripple issues, and inconsistent power, bad regulation, and random OS crashes.  If spending lots of time trying to debug systems that can't be debugged because they have "random" power as an input sounds like fun then precede ...

'afternoon DAT.
This particular PSU was spanked in virtually any semi-competent review for developing excessive noise and ripple - even going out of spec on higher loads.
This is a clear example of a manufacturer cutting corners by using an inadequate number/quality of capacitors to even the ripple out.

Yeah, for anyone still unable to  grasp it:
#define gamer-grade "overpriced low-end product 'upgraded' with a shitload of blue LEDs in an attempt to sell it as something more than it actually is"

For the same uninformed crowd, world's best PSU platform is currently Seasonic Platinum.

So the cards really don't pull much power through the PCIe bus and most of it will come through the 6 pin connectors. I guess that removes the first option, I won't be able to run four 6pin connectors on each 12V rail if they're loaded down with 75W each. I can still add one additional PCI connector on each rail and still be under the 20 amp mark on each rail.

Looking at the actual topology of the supply, it is actually a single rail split four ways for overcurrent protection as opposed to four physically separate rails. I guess I'll have to take it to work and actually load down the rails to be sure, but if the supply does make 75A between all three rails I should be ok, at least stock or undervolted.

Just to be clear, I'm not going to use molex to PCIe adapters. I'm planning on soldering connectors onto the PSU. I might have to save up for a good 1000W supply eventually, but if I can make a $60 supply work for now I'm going to give it a shot. Thanks for the opinions guys.

All contemporary "multi-rail" PSUs use what's best called "virtual-rails".
Redundant circuitry for each rail would be prohibitively expensive, therefore a single 12V rail is divided into a number of "virtual rails" by means of a OCP (overcurrent protection) circuit.

Since you seem to have made up your mind, I recommend that you solder one additional PEG-6 connector to both rail 2 and rail 4, and two PEG-6 connectors to rail 3.
The reason for that is, the motherboard won't draw a lot of 12V current, neither will the fans and drives.

Best of luck!

[MrTeal]

So the cards really don't pull much power through the PCIe bus and most of it will come through the 6 pin connectors. I guess that removes the first option, I won't be able to run four 6pin connectors on each 12V rail if they're loaded down with 75W each. I can still add one additional PCI connector on each rail and still be under the 20 amp mark on each rail.

Looking at the actual topology of the supply, it is actually a single rail split four ways for overcurrent protection as opposed to four physically separate rails. I guess I'll have to take it to work and actually load down the rails to be sure, but if the supply does make 75A between all three rails I should be ok, at least stock or undervolted.

Just to be clear, I'm not going to use molex to PCIe adapters. I'm planning on soldering connectors onto the PSU. I might have to save up for a good 1000W supply eventually, but if I can make a $60 supply work for now I'm going to give it a shot. Thanks for the opinions guys.

All contemporary "multi-rail" PSUs use what's best called "virtual-rails".
Redundant circuitry for each rail would be prohibitively expensive, therefore a single 12V rail is divided into a number of "virtual rails" by means of a OCP (overcurrent protection) circuit.

Since you seem to have made up your mind, I recommend that you solder one additional PEG-6 connector to both rail 2 and rail 4, and two PEG-6 connectors to rail 3.
The reason for that is, the motherboard won't draw a lot of 12V current, neither will the fans and drives.

Best of luck!

As I said, if possible I'd like to use this supply as I already have it. An 800W Seasonic would be a wonderful choice, but it would also cost me $200 more than I paid for the OCZ supply. It's obviously not a 1010W supply, but if I can get 600W out of the 12V rail that's all I really need. I don't plan to run any 12V fans or HDDs off the supply, so there really shouldn't be much draw other than the CPU and GPUs.

If testing goes poorly, would there be a huge disadvantage to running the OCZ unmodified to two of the cards, and running the other two off a Corsair VX-450w I have sitting around? It's group regulated so I'm not sure how well it like not being on loaded on the 3.3 and 5V rails. Some people seem to have good luck with a dual PSU setup, so that could be another option.

[jake262144]

If testing goes poorly, would there be a huge disadvantage to running the OCZ unmodified to two of the cards, and running the other two off a Corsair VX-450w I have sitting around? It's group regulated so I'm not sure how well it like not being on loaded on the 3.3 and 5V rails.

There should be no disadvantage whatsoever. Use the VX-450W exclusively for 12V and never care how far out of spec its minor rails jump. As long as 12V doesn't fall below spec minimum you're ok.
A power resistor (e.g. 5W) between neutral and 5V might mitigate the crossload situation somewhat.