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Dual rail PSU connections and power consumption questions

post #1 of 8
Thread Starter 
I just bought a used Zotac GTX 580 Amp Edition and I am trying to figure out the best way to route the power to it. The card is factory overclocked and I may overclock it farther in the future. My CPU is a 3570k currently running at 4.2 Ghz and will also be overclocked farther in the future. I have a dual rail PSU and I need to figure out which rails the CPU and the two PCI-E cables connect to so I can make sure the GPU and CPU are not drawing from the same rail.

The PSU is an OCZ 700W Modxstream Pro. I saw it on sale about 1 1/2 years ago for $50 shipped and bought it without doing any research. I know it has had bad reviews in the past, but I need to do some more research on it. They have it listed in Tier 3 on this site. Does anyone know anything about this PSU? Money is tight, but should I look for something better in the near future? I will be using this PSU for right now though.

The PSU has two 25 amp rails with a total of 552 watts available. I know I can only pull 552 watts total, but i'm not sure if that means I can pull a full 25 amps (300w) off of one rail as long as the other isn't maxed or if each rail can really only put out 276 watts.

Here us a link showing power consumption of the 580 amp edition: GTX 580 Amp power consumption.

It says just the card uses 205w average, 237w peak, and 321w running furmark stability test. The card uses an 8 pin and a 6 pin cable. Do you think at these wattages it is safe to run both cables to one rail or should I (if I can) run the 6 pin to the same rail as the CPU and run the 8 pin to it's own rail?

I haven't been able to find anything from OCZ saying which rails each cable connects to, but I did find a review of the 600w version here: OCZ 600w Review

It says that all the cables permanently attached to the PSU are connected to one rail and all the modular cables are connected to the other rail. If that is correct than I only have the choice of connecting both GPU power cables to one rail.

So as long as I understood the PSU review correctly I think I answered my own question on connection the GPU. I only have one choice and that is to connect both PCI-E cables to a single rail. Should I be ok running this card off one rail and do you have any opinions on the OCZ PSU quality? It's the ModXStream, not the better Modstream.
post #2 of 8
I've been running an ModXStream for over 5 years without any issues. Mine's not modular, though.

As for the rails, you can generally ignore the fact that they exist. I doubt the system you have will pull enough from the rails to cause it to shut down. The PCIe connectors are almost definitely on a different rail from the CPU connectors.

Power Supply rails are like the circuit breakers in your house, or fuses in your car- they don't change the amount of power you can draw, but segment it for safety. All your 'rails' come from the same source in the power supply internally- there's just a sensor on each rail that shuts the supply off if the rail goes over the set current. Like how your house only has one power source but a lot of breakers in it.

So yes, you can draw up to the 25A on a rail before it'll shut off. There should be another, third sensor that senses both rails for the overall current limit.
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post #3 of 8
ModXStream is not really a great PSU its main flaw is its a group regulated unit so voltage regulation is pretty bad
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post #4 of 8
Thread Starter 
GPU is in the mail and I should have it in the next couple days. After I get it running and test it a little, the first thing i'm going to do is install Crysis 2 with the high resolution texture pack. That should be a good test to make sure my ebay card works as it should.

So I guess I should be able to game with my current PSU, but if I tried to benchmark the card on something like Furmark I would trip the 25 amp rail.


Quote:
Originally Posted by shilka View Post

ModXStream is not really a great PSU its main flaw is its a group regulated unit so voltage regulation is pretty bad
What is bad about a group regulated PSU? I would assume the voltage will go higher or lower than optimal during certain situations which may cause stability problems. Would that require me to run a higher voltage at the same clock speed to prevent a crash during the dip in voltage? Is that the only problem or will the voltage changes harm any sensitive components like on the motherboard?


Edit: Just opened my front door after posting this and the GPU is here. Time to install the new card and an extra case fan.
post #5 of 8
Voltage regulation means the system will be less stable, you should just replace it its not very good even if it was not group regulated
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post #6 of 8
Thread Starter 
The problem is I don't really have the money. If bad voltage regulation just means that I need to run a slightly higher voltage to keep the system stable, then I am ok with that as long as the fluctuating voltage does not damage any components. That may cause a problem in the future when I decide to push the CPU to it's limits and can't afford to add extra voltage, but it is currently stable and has been for 1 1/2 years.

Do you think the PSU is going to die or damage any of my components? I know anything is possible, but how likely is it to happen? Has there been many reports of this PSU failing? I know back around 2008 they had a lot of problems, but I have read that OCZ switched to better parts in some PSU's after they had problems. I don't know if this specific model was updated though.
post #7 of 8
Quote:
Originally Posted by AllTracTurbo View Post

The problem is I don't really have the money. If bad voltage regulation just means that I need to run a slightly higher voltage to keep the system stable, then I am ok with that as long as the fluctuating voltage does not damage any components. That may cause a problem in the future when I decide to push the CPU to it's limits and can't afford to add extra voltage, but it is currently stable and has been for 1 1/2 years.

Do you think the PSU is going to die or damage any of my components? I know anything is possible, but how likely is it to happen? Has there been many reports of this PSU failing? I know back around 2008 they had a lot of problems, but I have read that OCZ switched to better parts in some PSU's after they had problems. I don't know if this specific model was updated though.

You cant fix loose voltage regulation with bumping the voltage, that is like putting brand new tires on a rusting 50 year old beat up car its still a 50 year old car
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post #8 of 8
Quote:
Originally Posted by AllTracTurbo View Post

The problem is I don't really have the money. If bad voltage regulation just means that I need to run a slightly higher voltage to keep the system stable, then I am ok with that as long as the fluctuating voltage does not damage any components. That may cause a problem in the future when I decide to push the CPU to it's limits and can't afford to add extra voltage, but it is currently stable and has been for 1 1/2 years.

Do you think the PSU is going to die or damage any of my components? I know anything is possible, but how likely is it to happen? Has there been many reports of this PSU failing? I know back around 2008 they had a lot of problems, but I have read that OCZ switched to better parts in some PSU's after they had problems. I don't know if this specific model was updated though.


No. As long as the PSU stays within spec, imperfect regulation won't hurt anything. Group regulation is only a problem if you present a huge load on the 5v or something like that. Just use the thing and don't loose sleep over it. You're not coming even close to the supply's ratings, either.
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