View Full Version : Help me understand +12v
I'm looking at a 7900gtx & Santa Ana 1210.... The 7900gtx recommends at least 22a on the 12v.
I have a Fortron 350W that is rated at +12v@15a, -12v@0.8 (non-dual 12v).
I also have a dual 12v Fortron 300W that is rated at +12v1@16a, +12v2@16a, -12v@0.8
Question is: Is the 300W FSP the better choice? Is it an effective 31.2a to the 12v?
If neither of these are good choices, could somebody recommend a PSU? I would like to stick with FSP (or Sparkle).... they have never let me down.
killermiller
11-19-06, 06:28 PM
I don't think that is a recommendation, it is more like a requirement, you cant use either of those psu's with that card.
The dual rail psu shares those 16 amps. That is the maximum that each rail can use, but they cannot both draw 16 amps @ the same time.
mantralord
11-19-06, 06:36 PM
I don't think that is a recommendation, it is more like a requirement, you cant use either of those psu's with that card.
The dual rail psu shares those 16 amps. That is the maximum that each rail can use, but they cannot both draw 16 amps @ the same time.
The 7900GTX draws 84.2W max (http://xbitlabs.com/articles/video/display/ati-x1950xtx_7.html), which comes out to almost exactly 7A. Therefore, it should be enough. nVidia's recommendations are just what idiot gamers want to hear.
Aphex_Tom_9
11-19-06, 06:47 PM
The 7900GTX draws 84.2W max (http://xbitlabs.com/articles/video/display/ati-x1950xtx_7.html), which comes out to almost exactly 7A. Therefore, it should be enough. nVidia's recommendations are just what idiot gamers want to hear.
more like what they expect your computer to need after adding the card to your system.
The 7900GTX draws 84.2W max, which comes out to almost exactly 7A. Therefore, it should be enough.
Are you saying either PSU may be enough?
I would rather use the 350W, So, what would you expect the rest of the 12v to use? Here's the full specs: +3.3V@28A, +5V@32A, +12V@15A, -5V@0.3A, -12V@0.8A, +5VSB@2A
I have 3 fans, 2 HDDs, 2 cd-drives, etc..... the normal stuff.
killermiller
11-19-06, 09:12 PM
The 7900GTX draws 84.2W max (http://xbitlabs.com/articles/video/display/ati-x1950xtx_7.html), which comes out to almost exactly 7A. Therefore, it should be enough. nVidia's recommendations are just what idiot gamers want to hear.
The video card alone would consume almost half of the output on the 12v rail. I would be willing to bet that those psu's that you described will not power your system and peripherals. I used to have a s754/chaintech/2 hdds/1 dvd/1 CDRE and I upgraded to a 6600 and had a 350w and when I installed the VC my system would not post because the VC was not getting enough power.
You could always give it a shot, but I would not get your hopes up. Even if it did work you may be faced with stability issues, especially if you oc.
SeraphZero
11-20-06, 11:56 AM
Better safe than sorry. I'd get something with a little bit bigger ampage on the 12V+ line just to be safe. It shouldn't be that much more expensive.
WonderingSoul
11-20-06, 01:17 PM
The 7900GTX draws 84.2W max (http://xbitlabs.com/articles/video/display/ati-x1950xtx_7.html), which comes out to almost exactly 7A. Therefore, it should be enough. nVidia's recommendations are just what idiot gamers want to hear.
I wouldn't throw the words "idiot gamers" around so loosely... I for one take offense to that.
And a 7900GTX IS A GAMING CARD. I am almost dead positive those PSUs will not be able to power a GTX. I've talked to an eVGA tech rep and they said specifically 20AMPs on a PSU is required to power up a 7900GT, that is just a stardard GT, not a GTX. And 350W isn't much power at all.
My 480w 18A barely powered my 7900GT. Everytime I would overclock it would just loose so much power and almost BSOD. The recomended 20A is more like "have it or suffer"
If you got money to spend on a GOOD PSU I love my Silverstone Zeus 56ZF 560W; 38A@12v (and it is a single 12v rail as well).
mantralord
11-20-06, 01:49 PM
I wouldn't throw the words "idiot gamers" around so loosely... I for one take offense to that.
And a 7900GTX IS A GAMING CARD. I am almost dead positive those PSUs will not be able to power a GTX. I've talked to an eVGA tech rep and they said specifically 20AMPs on a PSU is required to power up a 7900GT, that is just a stardard GT, not a GTX. And 350W isn't much power at all.
My 480w 18A barely powered my 7900GT. Everytime I would overclock it would just loose so much power and almost BSOD. The recomended 20A is more like "have it or suffer"
If you got money to spend on a GOOD PSU I love my Silverstone Zeus 56ZF 560W; 38A@12v (and it is a single 12v rail as well).
hurr guys were gamerz lol qft ftw chuck norris anime
Just because you moved to a higher power PSU and it magically fixed your problems doesn't automatically mean that whatever wattage your old PSU claimed to output wasn't enough, which is sadly the final conclusion most gamers/overclockers reach in this situation. The old unit's build quality, actual power capabilities, ripple, compensation for inherent instability in your building's wiring, and the general power quality all come into play. For example, a non-P4 system with a card like that can expect to draw 250W in a worst case scenario. If you try to power it with a Powmax 500W (which is good up to ~250W, barely enough for the max), you will probably experience stability issues simply because the quality of the power is poor. If you replace the Powmax with a 300W Delta or Fortron, the situation will be different.
In the SPCR forums, there's a thread where people are powering systems like these all the time with 300W units.
greenmaji
11-20-06, 02:30 PM
@Nabis.. what is the maximum Wattage that can be applied to the 12V rails as printed on the PSU?
If its 264+Watts (IE 22amps+) you should be fine.
If not I would look into getting a different PSU.
@killermiller.. Older PSU's were desinged with computers that needed the 5V rail in mind, the 12V rail was underpowered.
@mantralord.. try not to insult the members, regardless of the advice they give, thanks :)
Flasher702
11-20-06, 03:09 PM
@nambis
The 300w dual-rail one should be able to power it, if it's new, depending on what else is in your PC, but not by a very big margin. It has enough 12v amperage, but with only 300w total output you could run into some trouble. The total 12v amperage between the two 12v rails depends on the design of the PSU and is it's own rating (much like the 3.3v+5v ratings that were important to PSUs for PCs of olde). It is less than 32a, but obviously more than 15a making the dual-rail PSU the better choice. Some companies publish combined +12v amperage ratings, others do not. PSUs with no published combined +12v amperage rating should be treated with suspision.
Unless that 300w psu you have is new in an almost never-used condition and the rest of your system is small and you aren't OCing you should get a new PSU. Electrolite capacitors age and loose effeciency so it's a good idea to get new PSUs when you upgrade other components. You don't want to run your rails near maximum capacity either. Here's a good PSU wattage calculator (http://extreme.outervision.com/PSUEngine). Your system, without OCing, 1 SATA drive, 1 DVD-RW, 1 120mm exhaust fan comes in at 286w at full-load. But if we slap a years worth of capacitor aging on there it comes to 343w. So you can see that you're cutting it pretty close.
I'd say a new ~400w PSU is in order.
what is the maximum Wattage that can be applied to the 12V rails as printed on the PSU?
If its 264+Watts (IE 22amps+) you should be fine.
If not I would look into getting a different PSU.
I'll have to take it out of the case sometime soon and check it out. Thanks for the info.... and I have these FSP's exactly for the reason that you mentioned about the +5v. This happens to have 32a on the +5v for an old A7N8X-e, which needs crazy +5v.
This is also exactly the point why I'm asking the question, all while hoping not to get an answer like, "just get a 1.21 Gigawatt PSU"....
We all know that even some 1kw PSU's can have trouble powering an old mobo like the A7N8X-e, therefore my initial question of how much +12v I'll need.
Here's an example.... If we're bench-racing, even this 1kw PSU wouldn't help me with the 7900GTX's minimum 22a.
http://www.newegg.com/Product/Product.asp?Item=N82E16817104024
BTW - It's not old at all... about 6 months - also, I don't have a problem buying what I need, I just want to know what I need to buy before I buy it, ya know?
WonderingSoul
11-20-06, 05:49 PM
I'll have to take it out of the case sometime soon and check it out. Thanks for the info.... and I have these FSP's exactly for the reason that you mentioned about the +5v. This happens to have 32a on the +5v for an old A7N8X-e, which needs crazy +5v.
This is also exactly the point why I'm asking the question, all while hoping not to get an answer like, "just get a 1.21 Gigawatt PSU"....
We all know that even some 1kw PSU's can have trouble powering an old mobo like the A7N8X-e, therefore my initial question of how much +12v I'll need.
Here's an example.... If we're bench-racing, even this 1kw PSU wouldn't help me with the 7900GTX's minimum 22a.
http://www.newegg.com/Product/Product.asp?Item=N82E16817104024
BTW - It's not old at all... about 6 months - also, I don't have a problem buying what I need, I just want to know what I need to buy before I buy it, ya know?
I recommend the PSU in my sig. People have been able to run two 7900GTX on them no sweat. It can power my full rig without a hitch as well. If you're looking for more power the 65ZF or 75ZF are also great choices.
greenmaji
11-21-06, 08:57 AM
Well, since your PSU is one of the old ones with big 5V power, you'll need something else.
The silverstone in the above rig will power a monster machine, just short of ANYTHING.
This is your baseline ~22.5 total 12V amps for $56.00+S/H
http://www.ewiz.com/detail.php?p=PS-E5140GH&c=fr&pid=c62bb0c4e9d2445f5a73431689c059a23b17e186bcde9c 607039e67184e8e9e1
$11 more gets you this. ~30 12V amps. (PLENTY of headroom)
http://www.ewiz.com/detail.php?p=PS-E5150GH&c=fr&pid=c62bb0c4e9d2445f5a73431689c059a23b17e186bcde9c 607039e67184e8e9e1
The silverstone in the above rig will power a monster machine, just short of ANYTHING.
This is your baseline ~22.5 total 12V amps for $56.00+S/H
$11 more gets you this. ~30 12V amps. (PLENTY of headroom)
Dumb question... how'd you figure the amp output, with the information given on the link?
The Silverstone is also $130 - Nice piece of equipment, but somewhat overkill.
Using these types of theories, what makes the above mentioned PSU's any different than this unit -
http://www.newegg.com/Product/Product.asp?Item=N82E16817255010
500w w/ +12v@28a? .... a name? .... the reviews seem to be decent.
And I'm not saying I would purchase this, I am just playing devil's advocate to try to understand.
New question -
What makes dual +12v necessary? For my application, it isn't needed.... correct?
What do people have in their machine that makes a dual +12v absolutely necessary?
freakdiablo
11-21-06, 10:25 AM
New question -
What makes dual +12v necessary? For my application, it isn't needed.... correct?
What do people have in their machine that makes a dual +12v absolutely necessary?
basically, dual +12v is, i think, for dual gfx cards like sli or crossfire. I also heard someone say it was to give the cpu its own dedicated rail. for only one it doesnt matter.
Flasher702
11-21-06, 01:41 PM
New question -
What makes dual +12v necessary? For my application, it isn't needed.... correct?
What do people have in their machine that makes a dual +12v absolutely necessary?
Splitting the +12v load up between multiple semi-independent rails helps to keep the voltages stable and makes it easier to pump out more total +12v amperage without catching things on fire (running the +50a of +12v through a single PCB trace seems like maybe a bad idea to me anyway, PSU makers have split it up amoungs 4 rails). Motherboards now have additional inputs for +12v, as do high-end GFX cards. So a device (like CPU or GPU) can go from no load to full load on one rail without affecting devices on the other rails.
What makes you "need" dual +12v? Nothing really, if your single +12v line is up to the task. I think the idea was that an uber-high-wattage GFX setup firing up could cause a momentary dip in the +12v that could cause CPU instability. Independent rails isn't a new concept for overclockers (dual PSUs FTW!), they just put them into one box to help main-stream users deal with SLI and Prescott. Prescott went away, we can all hope that power-sucking monstrosities of GFX setups also go away soon, but multiple independent rails are still a good idea.
greenmaji
11-22-06, 03:21 AM
Dumb question... how'd you figure the amp output, with the information given on the link?
The Silverstone is also $130 - Nice piece of equipment, but somewhat overkill.
Using these types of theories, what makes the above mentioned PSU's any different than this unit -
http://www.newegg.com/Product/Product.asp?Item=N82E16817255010
500w w/ +12v@28a? .... a name? .... the reviews seem to be decent.
And I'm not saying I would purchase this, I am just playing devil's advocate to try to understand.
Max bearable on the 3+5 - total wattage / 12
The OEM of the PSU (found by looking up the UL # on the PSU and entering that info here http://database.ul.com/cgi-bin/XYV/template/LISEXT/1FRAME/index.htm ), there's a short list of decent PSU makers, sadly. Could be worse I suppose, there could be less. Poor OEM's do things like test the PSU's power rating at room temperature, or lower then average room temp, rather then operating temp, use poor quality components and some in the past have outright changed the design after getting UL to something inferiour :eek:
The one you linked by the way is rated by that company to be 69% power effecent while the ones I linked are 80%
And no, multiple rails isnt nessary, another train of thought is to put fans, hardrives and pumps on one rail to isolate electrical noise as well. Big quality single rail PSU's seem to fair best under high loads, power hungry hardware, however (no crossloading of the multiple rails to get power to the component that needs it)
It depends on what you are running on that system. If you're running a dothan, for instance (max draw 3A OCed), you'd have plenty of power left. However, if you are running an OCed pentium D, that alone will chew up your 15A by default.
The 7900GTX draws 84.2W max (http://xbitlabs.com/articles/video/display/ati-x1950xtx_7.html), which comes out to almost exactly 7A. Therefore, it should be enough. nVidia's recommendations are just what idiot gamers want to hear.
Yeah, but if he's got a P4 sucking 100W of juice, that 15A is going to be far from adequate. It all depends on the power draw of the rest of his system.
Splitting the +12v load up between multiple semi-independent rails helps to keep the voltages stable and makes it easier to pump out more total +12v amperage without catching things on fire (running the +50a of +12v through a single PCB trace seems like maybe a bad idea to me anyway, PSU makers have split it up amoungs 4 rails).
That's a 100% absolute, pure, and total freaking marketing lie. The only reason multiple rails exist is because of the arbitrary ATX standard that specifies no more than 20A to any single device. It's not so much a rail as an amperage cap (the term rail is just a marketing gimmick). Moreover, the rationale is total bunk. If PSUs really needed multiple rails to be safe, the why don't we see multi-rail PSUs in server applications? We don't; in fact the best and most powerful server-grade PSUs out there use a single, powerful, 12v rail.
There is no such thing as independent rails; all that happens is that amperage to any device is capped at 20 and the rest spills over. The spill over is the second, third, fourth, etc "rail."
It depends on what you are running on that system. If you're running a dothan, for instance (max draw 3A OCed), you'd have plenty of power left. However, if you are running an OCed pentium D, that alone will chew up your 15A by default. Right... I was speaking of the Santa Ana 1210, and I do not know what type of draw it has.
Right... I was speaking of the Santa Ana 1210, and I do not know what type of draw it has.
The TDP of the Opteron 1210 is 103W, which is probably overstated, though it'll easily reach that if overclocked. You'll probably need a new PSU. I'd recommend a psu with a single powerful rail such as the OCZ powerstream 520 or the Silverstone Zeus 560.
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