How many 12V Amps are really necessary?

PSUs: The source of DC power for all components in the PC & often a big noise source.

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PzyMazter
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How many 12V Amps are really necessary?

Post by PzyMazter » Thu Sep 01, 2005 3:49 pm

Basically what it amounts to is the requirements you see posted from time to time as a minimum. I have spent the better part of this last week researching power supplies, and I have decided on a Seasonic S12, the only sticking point being the size.

Some video cards, such as the 7800GTX, specifically state to require 26A on the 12V rail for a single card. The 430 only provides 29A on split rails, which I was advised by OCZ to be insufficient for split rails to power a gaming system using performance memory. They informed me 28A on a single rail was enough, but I need 33 for split rails. Is this true? I mean, it seems to me that this could be highly relevent, but I am just not sure about it. I have never taken physics nor have I ever learend much about the basics of electricity in computers besides the articles on this website, and this leads me to confusion galore.

I have also read that DFI specifically REQUIRES a 480 watt PSU with 25A minimum on the 12V rail to run their S939 SLI motherboard, completely in contradiction to some of what I've read here in terms of power requirements by wattage.


It's all confusing to me and I just don't know who to believe. It seems to me that if BFG tells me that to run a 7800GTX I need 26A of power that it has to be the truth, but is it? This place in particular seems to always claim need for very small power supplies, generally small power supplies having poor 12V amps. What does this really mean?

I should mention that the reason I am buying this power supply is to run my current system and my upgraded system that I will be purchasing in the next year or 2. I will be needing this power supply until the warranty is dead, at least. I don't want to cause problems with upgrading to S939 down the road or whatever looks good as time goes on. But my current system is as follows, not originally designed as silent, though I wish I had spent more time here in advance :/

Athlon 64 3200+ Clawhammer S754
ASUS K8V Deluxe (Cool n Quiet capable) w/ VIA K8T800 vanilla
2x 512 OCZ PC3200 DDR400 Enhanced Latency Rev 2 Memory
1x 5400 RPM Western Digital 40GB PATA, 1x 7200 RPM Seagate 120GB PATA, 1x 7200 RPM Seagate 300GB SATA.
Network card, wireless linksys one that never seems to work very well, WMP54GS
Sound card, Audigy 2
Soon to be installed PCI TV Tuner card
Soon to be upgraded to 6800Ultra or GT video card, currently GeForce FX 5900NU


I have a 460watt Enermax OEM PSU that looked cheap when I got it, but now I want a quality and quiet (!) one with thermal sensors so that Cool n Quiet can actually work for anything.

But as I say, this is my current system that WILL sustain at least one more video card and cpu/mobo upgrade, possibly memory too. I want to get one power supply to rule them all, and it seems to me that the Seasonic S12 430 is just not going to cut it. And since that won't be enough and the 500 will still only provide 31A on the 12V rail, I probably should go for a whopping 600? Money is not too big of an issue for this particular upgrade, but I want to stick with my new PSU. I realize that everyone advises against such a large one, but if there's no difference in noise between the S12 500 and 600, as was implied through the review posted on this site, why not? It's all because of the 12V amps and long term reliability.

But, I really am not well educated overall to the situation. Help on what to do, how many amps I really need, and other such matters is greatly appreciated!

Thanks.

Devonavar
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Post by Devonavar » Thu Sep 01, 2005 4:11 pm

Have you read the recently posted article about power distribution yet? That's a good place to start. Also, take a look at the PSU fundamentals article, particularly the part about "real power usage" on page four. Take a look at this thread for information about what the split rails really mean for your computer (and why they don't matter all that much).

Fairly good information about how much power a VGA card consumes can be found on Xbit Labs, or consolidated in this forum thread (most of the information comes from Xbit Labs).

What the VGA card manufacturers tell you is, quite frankly, BS. Power supplies power a computer system, it's impossible for a single component to "require" 33A. The VGA card companies will tell you to buy a high capacity power supply because they have no idea what the rest of your system is running, so they assume the worst (Dual Prescott CPU, 6 HDDs, heavy overclock, etc.). Basically, when they "require" a certain amperage, they're covering their asses so that you can't blame for recommending a power supply that caused their cards to fail.

As configured, your system is quite similar to the system we measured in the power distribution article I linked to above. That system drew 125W at full CPU load, ~8A of which are on the +12V line. If you wish, add in another ~6A for the 6800GT as a VGA load (measured separately). Call it ~200W DC. Now, add 30% headroom for peaks, and you're at 260W. Believe me, the Seasonic 430W is plenty.

If you really want to future-proof yourself (and you insist on using a second VGA card), go for the 500W. You'll be glad of the PCIe connector. Getting the 600W is pointless.

Devonavar
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Post by Devonavar » Thu Sep 01, 2005 4:12 pm

Devonavar wrote:Have you read the recently posted article about power distribution yet? That's a good place to start. Also, take a look at the PSU fundamentals article, particularly the part about "real power usage" on page four. Take a look at this thread for information about what the split rails really mean for your computer (and why they don't matter all that much).

Fairly good information about how much power a VGA card consumes can be found on Xbit Labs, or consolidated in this forum thread (most of the information comes from Xbit Labs).

What the VGA card manufacturers tell you is, quite frankly, BS. Power supplies power a computer system, it's impossible for a single component to "require" 33A. The VGA card companies will tell you to buy a high capacity power supply because they have no idea what the rest of your system is running, so they assume the worst (Dual Prescott CPU, 6 HDDs, heavy overclock, etc.). Basically, when they "require" a certain amperage, they're covering their asses so that you can't blame for recommending a power supply that caused their cards to fail.

As configured, your system is quite similar to the system we measured in the power distribution article I linked to above. That system drew 125W at full CPU load, ~8A of which are on the +12V line. If you wish, add in another ~6A for the 6800GT as a VGA load (measured separately). Call it ~200W DC. Now, add 30% headroom for peaks, and you're at 260W. Believe me, the Seasonic 430W is plenty.

If you really want to future-proof yourself (and you insist on using a second VGA card), go for the 500W. You'll be glad of the PCIe connector. Getting the 600W is pointless.
By the way, Welcome to SPCR!!!!!!!!!!!!

PzyMazter
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Post by PzyMazter » Thu Sep 01, 2005 7:19 pm

Unfortunately, I had already read all of them and was unable to draw any specific conclusions. Generally I noticed a LOT about wattage and NOT a lot about amperage. I understand that the total wattage required to power my system could easily be handled by 430 watts, but it's really all about the 12v rail's amp rating that seems relevent.

I should mention that I understand that I could probably power my current system with a 350 watt psu, but that isn't exactly what I understand.

Perhaps the problem stems from my lack of any knowledge period over what the 12v amp rating means. I'll try googling, but I just want to be safe.

And finally, why should I get 500 over 600 if there is absolutely NO difference in noise? Are there any reasons why I should opt for 500 over 600 if price is the same (well like $6 more)? Would this not theoretically "future proof" me even better? It also has more connectors iirc.

Oh, and
Devonavar wrote:
By the way, Welcome to SPCR!!!!!!!!!!!!
Thanks :)







And as a post script edit, what kind of overclocking would we be talking to require a greater power supply?

sthayashi
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Post by sthayashi » Thu Sep 01, 2005 8:00 pm

PzyMazter wrote:Unfortunately, I had already read all of them and was unable to draw any specific conclusions. Generally I noticed a LOT about wattage and NOT a lot about amperage. I understand that the total wattage required to power my system could easily be handled by 430 watts, but it's really all about the 12v rail's amp rating that seems relevent.
In DC systems, Wattage = Voltage * Amperage. From the watts, you can estimate Amperage.
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PzyMazter
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Post by PzyMazter » Fri Sep 02, 2005 4:17 pm

Would a 430 be able to power a "modern" gaming PC over the next 3 years (warranty length)? I plan on upgrading to SLI capability at some point but the 12V amps are so much below recommended minimum that it really does make me feel concern, particularly for the future and particularly if I have to overvolt my memory any more than I already am, or any overclocking I may end up doing.

If you really and honostly can tell me that 430 watts would be enough with the 12V amp ratings of only 29 combined for running modern video cards in a modern computer (meaning I will upgrade the cpu/mobo/video card and whatnot) even in SLI with light overclocking/overvolting (my memory requires at least 2.8V to run at SPD), then that's all I need to hear.

sthayashi
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Post by sthayashi » Fri Sep 02, 2005 8:27 pm

PzyMazter wrote:Would a 430 be able to power a "modern" gaming PC over the next 3 years (warranty length)? I plan on upgrading to SLI capability at some point but the 12V amps are so much below recommended minimum that it really does make me feel concern, particularly for the future and particularly if I have to overvolt my memory any more than I already am, or any overclocking I may end up doing.

If you really and honostly can tell me that 430 watts would be enough with the 12V amp ratings of only 29 combined for running modern video cards in a modern computer (meaning I will upgrade the cpu/mobo/video card and whatnot) even in SLI with light overclocking/overvolting (my memory requires at least 2.8V to run at SPD), then that's all I need to hear.
I generally never respond when someone asks if a PSU is sufficient for their overclocking needs. Because in my opinion, when you overclock and/or overvolt, all bets are off with regard to power consumption and stability. i.e. If you have an unstable system, where does your problem lie, the PSU I suggested or your OC'ing?

However, I feel like making a minor exception in your situation. I believe that the S12-430 should work for a modern gaming PC. The numbers suggest that they would. I can't tell you whether it'll last 3 years or not. Do you intend to not change your system at all within the next 3 years?
[size=75][url=http://www.twolf1300.net/sthayashi/SPCR/systems.html]My Power Rig, Storage Rig, HTPC and Main Rig[/url][/size]

PzyMazter
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Post by PzyMazter » Fri Sep 02, 2005 10:04 pm

I do intend to upgrade my system over the next 3 years and I have absolutely no choice but to overvolt my memory, at least as things stand now.

I intend on upgrading to a socket 939 CPU or the modern equivilent as soon as my A64 3200+ socket 754 Clawhammer can no longer stand sufficient for modern gaming. More than likely this will be as a result of AGP limitations and modern video cards than one of necessity for CPU power.

But lets say I plan on upgrading to a system utilizing the full power of a socket 939 A64 SLI setup with dual top of the line video cards and no overclocking. And lets say I won't be doing this until NVIDIA has had time to work on a newer line of cards and ATI has a counter to the 7800 series. Could I rely on a 430 watt PSU with 29 amps on the 12V rail? Or would it be better to rely on 500 or even 600 watt psu with 31 or 36 amps on the 12v rail for stability's sake?

I just want to use the power supply until the warranty is dead. Buying power supplies more often than that just seems wasteful, particularly if by buying a larger than necessary one now, that could be avoided.


Again, the only overclocking I'm likely to do is memory and that's out of NECESSITY. But it does throw in another factor as I have no clue how raising the voltage to 2.8 from default 2.5 affects anything.

Kwiet
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Post by Kwiet » Sun Sep 04, 2005 2:22 am

Pzy,
My HTPC runs a Socket 939 3000+ processor, overclocked X700 Pro 256MB card, two hard drives, three case fans and a gig of DDR on a Zalman 400W power supply with a single 15A 12V rail. My new motherboard is here so I can overclock the CPU although I don't plan on punching up the voltage. Since you are going for dual video cards, get the ATI style as it does not hammer the 12V rail as much. nVidia cards are much harsher on the 12V rail.
My next wazoo video card purchase will be a XBox360... much cheaper than dualies and comes with a bunch of other cool parts. :P My days of computer gaming are coming to a close as the cost is insane and much past of the cost of reality. If I want mega-horsepower gaming, I'll get a gaming machine that is made and programmed to do it.
A64 3000+ XP90-PanafloL blowing up and out of case vent Asus X700 Pro 256MB Artic Cooled
Zalman 400W PSU 3 Panaflo case fans 7V 1GB Corsair XMS CAS2 Seagate 80GB/Samsung 160GB/Theater 550 TV tuner

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