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Video card power.....

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a b U Graphics card
September 27, 2007 3:55:10 PM

I've checked out the bfg site on my 7950gt/oc 512..
They say I should have 22+ amps on the +12v rail.
My current supply is only giving 17A but my system runs stable.
Now, I tried to bump my system a few percentiles up from stalk but the system just reboots and I get the 3 sec
beep and no post!
Should I invest in a better psu?
The psu I'm using is an ANTEC SMARTPOWER 450....

ps. I think this might be causing some frame rate dropage as well...

More about : video card power

September 27, 2007 4:15:07 PM

Alot of system instability problems are caused by insufficient PSUs.

I'd definitely consider a PSU upgrade if your system is unstable. But if you're overclocking other things can hold you back as well, like memory timings...
a b U Graphics card
September 27, 2007 4:22:10 PM

My sig at bottom of my post tells what I've got...just messes up if I try to push my clocks,,etc
I should mention that I've got 2 +12 rails...1 is @15 amps and the second is @17 amps......
Does the second take from the first to make up for the lack of amps on the pci-e buss?
Related resources
September 27, 2007 4:27:41 PM

Have you loosened your memory timings in the BIOS when trying higher clock speeds?
a c 172 U Graphics card
September 27, 2007 5:12:41 PM

I also have a SP 450W. Yes, you have two rails, one at 15A and one at 17A. If my memory serves, they together can output about 28A. This is why you can run a card that requires 22A.

I'd love to be able to answer your question, but I have no idea what "I tried to bump my system a few percentiles up" means. What part of your system? FSB? Memory? Video core or memory? All of these? By how many is a few percentiles? What where the temps before and after you did this? Give us a few details other then it doesn't work if you want some help.
a b U Graphics card
September 27, 2007 5:20:28 PM

I tried setting the bios from auto to performance gamer and the system rebooted with a 3 sec. beep and then another 3sec. beep...continuously till I reset the bios.

Sorry, by pecentile I mean 20% over stock..if that helps..
September 27, 2007 5:20:43 PM

Remember, if a card has a 22A requirement it's assuming it's sharing a single 22a rail with the rest of the system. The 7950 GT only needs a portion of that.

If you have two 12v rails, even a dedicated 15a should be fine for a 7950GT.
September 27, 2007 5:22:05 PM

Try setting it to manual.... find out your memory's stock latencies and increase it a bit, then up the FSB manually.

Better yet... read on overclocking guide on the net before doing anything... your PSU sounds like it should be able to sustain a bit of overclocking. :) 
a c 172 U Graphics card
September 27, 2007 5:29:00 PM

I've heard of bios's that let you "auto overclock", but how they accomplish this probably varies depending on the motherboard. 20% might also be to much for your parts. Either try a lower percentage, or I also suggest learning how to "really do it". You might just need a small voltage bump to make that 20% stable. Or a 19.5% overclock might be work. If you know what you're doing, manually overclocking is better.
September 27, 2007 6:46:39 PM

cleeve said:
Remember, if a card has a 22A requirement it's assuming it's sharing a single 22a rail with the rest of the system. The 7950 GT only needs a portion of that.

If you have two 12v rails, even a dedicated 15a should be fine for a 7950GT.

I would have to dis-agree. Combined 22a on the 12v rails for a 7950GT.
EXAMPLE
my previous 305w psu
18a + 18a = 264w maximum combined wattage on the 12v rails (the 2 12v rails)
divided by 12 = 22a maximum combined amps on the 12v
September 27, 2007 6:52:50 PM

What does that prove?

The card does not draw all of the 12v power available, kpo6969.
12v is needed to run your system, even if you didn't have a videocard.

The manufacturers of the 7950 GT know this, and their requirement assumes a single 12v rail for the whole system. The 7950 GT does not need all those amps by itself.

That's why the single card requirement will be 22 amps, and two cards in SLI will require something like 29 amps...

...otherwise you'd need a 44 amp 12v rail to run 7950 GTs in SLI. Not likely.
September 27, 2007 6:56:08 PM

What else runs off the 12v (just asking?)
cpu- watts divided by 12 = ?
ram- xxxxxxxxxxxxxxxxxxx=?

I thought those have to added to the card's total?
Sorry if I'm incorrect.
September 27, 2007 6:59:19 PM

The 12v rails also take care of drives, fans, and in many cases - the CPU.
a c 172 U Graphics card
September 27, 2007 7:00:57 PM

kpo6969 said:
I would have to dis-agree. Combined 22a on the 12v rails for a 7950GT.
EXAMPLE
my previous 305w psu
18a + 18a = 264w maximum combined wattage on the 12v rails (the 2 12v rails)
divided by 12 = 22a maximum combined amps on the 12v


I think your post needs another edit, as it doesn't make any sense to me.

Quote:
Combined 22a on the 12v rails for a 7950GT.


Huh? What we're trying to say is that you don't need a single 12V rail that has 22A. If you have two rails, 15A and 18A, or 18A and 20A, then they probably combined can output enough amperage to drive the 7950GT/card in question.

Quote:
18a + 18a = 264w maximum combined wattage on the 12v rails (the 2 12v rails)


Huh? 18A + 18A = 432W. (assuming we are still talking about the 12V line. 18 + 18 = 36A. 36A * 12V = 432W, not 264W. If your 305W Dell PSU could only do 264W, then work backwards. 264W / 12V = 22A. Assuming that 264W figure is the total that the PSU can output, this 22A might be one a single line, or spread across two rails. What is likely going on is that you had two rails, each rail can output a max of 18A, but the two rails together can only do 22A.
September 27, 2007 7:07:23 PM

Just to clarify, what I'm saying here is that the 7950 GT does not, by itself, require 22 amps on the 12v rail.

The manufacturer recommends a 22 amp power supply because that 12v power is shared between the graphic card and other components like the CPU, hard drives, and fans. This is taken into account when they make the recommendation.

I believe (although I'm not 100% on this part) that power supplies with two 12v rails dedicate one to the motherboard (for CPU, fans, etc.) and one to the graphics card PCIe power connector.

Even though neither rail is 22 amps, the OP was worried that the largest of his two 12v rails is only 17 amps.
However, this rail would easily supply enough juice for the graphics card if it wasn't shared with the rest of the system.
September 27, 2007 7:10:03 PM

I'm sorry for even posting.
What I'm trying to say having one of your 12v rails @15a doesn't mean you can run the card.

4745454b
sorry for your confusion

I know the specs of the psu I had and what it can do.

Sorry for expressing an opinion, I will avoid getting jumped on for doing such in the future.
September 27, 2007 7:14:09 PM

johnnyq1233 said:
I've checked out the bfg site on my 7950gt/oc 512..
They say I should have 22+ amps on the +12v rail.
My current supply is only giving 17A but my system runs stable.
Now, I tried to bump my system a few percentiles up from stalk but the system just reboots and I get the 3 sec
beep and no post!
Should I invest in a better psu?
The psu I'm using is an ANTEC SMARTPOWER 450....

ps. I think this might be causing some frame rate dropage as well...

Your psu has 22amps which is boardline.
http://forums.guru3d.com/showthread.php?t=205763
Antec SmartPower 2.0 SP-450 22amps
September 27, 2007 7:16:26 PM

4745454b said:
I think your post needs another edit, as it doesn't make any sense to me.

Quote:
Combined 22a on the 12v rails for a 7950GT.


Huh? What we're trying to say is that you don't need a single 12V rail that has 22A. If you have two rails, 15A and 18A, or 18A and 20A, then they probably combined can output enough amperage to drive the 7950GT/card in question.

Quote:
18a + 18a = 264w maximum combined wattage on the 12v rails (the 2 12v rails)


Huh? 18A + 18A = 432W. (assuming we are still talking about the 12V line. 18 + 18 = 36A. 36A * 12V = 432W, not 264W. If your 305W Dell PSU could only do 264W, then work backwards. 264W / 12V = 22A. Assuming that 264W figure is the total that the PSU can output, this 22A might be one a single line, or spread across two rails. What is likely going on is that you had two rails, each rail can output a max of 18A, but the two rails together can only do 22A.

I know how to add
September 27, 2007 7:17:59 PM

No need to apologize, nobody's calling you any names. We're just trying to clear this up for you folks.

we can summarize the point thusly:

1. If you have one 12v rail under 22 amps, you might have trouble running the card

2. If you have more than one 12v rail - each under 22 amps - you probably WILL be able to run the card.

a c 172 U Graphics card
September 27, 2007 7:40:26 PM

kpo6969 said:
I know how to add


Are you sure about that? Is 18A + 18A = 36A? Does multiplying that 36A by 12V get you to 264?

I also chuckled a bit about the site you linked to. He's close, but not exact for the SP 450. My box says 440W for all rails, and 150W for the 5 and 3.3V rails. This leaves (at least) 290W for the 12V rails. (I said at least because not maxing out the 3.3 and 5V rails MIGHT allow for more power to be sent to the 12V rail, read the bottom of the first post.) 290W / 12V = 24.16A, a bit more then the 22A figure you and he quote.

Don't be sorry for even posting, thats not mine or cleeve's goal. The OP posted a question, and as much as you might deny it, there is some confusion about how a PSU works. If you are only going to get pissy and shut down, then you won't learn anything. If my math is wrong, feel free to show me where. Just don't expect me to believe you if you say, "some guy in some forum says it can do only 22A, so there!"
September 27, 2007 9:16:41 PM

4745454b said:
Are you sure about that? Is 18A + 18A = 36A? Does multiplying that 36A by 12V get you to 264?

I also chuckled a bit about the site you linked to. He's close, but not exact for the SP 450. My box says 440W for all rails, and 150W for the 5 and 3.3V rails. This leaves (at least) 290W for the 12V rails. (I said at least because not maxing out the 3.3 and 5V rails MIGHT allow for more power to be sent to the 12V rail, read the bottom of the first post.) 290W / 12V = 24.16A, a bit more then the 22A figure you and he quote.

Don't be sorry for even posting, thats not mine or cleeve's goal. The OP posted a question, and as much as you might deny it, there is some confusion about how a PSU works. If you are only going to get pissy and shut down, then you won't learn anything. If my math is wrong, feel free to show me where. Just don't expect me to believe you if you say, "some guy in some forum says it can do only 22A, so there!"

I thought I was done with this but just to show you you are incorrect.
You said
"Are you sure about that? Is 18A + 18A = 36A? Does multiplying that 36A by 12V get you to 264?"
No it doesn't
But
My 2-18a 12v rails have a maximum power wattage capacity of 264watts (printed on the psu label)
divide that by 12 = 22amps
Please reply with documentation to show I am incorrect.
I did not submit totals for that link so that may be wrong but I can read the label of my own psu.
September 27, 2007 9:21:07 PM

In most cases, separate 12v rails can't handle peak draw on both at the same time.

So yes, Two 18A 12v rails might only be able to provide less than 36 amps total between both when under load.
September 27, 2007 9:29:53 PM

4745454b,
In response to your statement:
"If my math is wrong, feel free to show me where. Just don't expect me to believe you if you say, "some guy in some forum says it can do only 22A, so there!"

1.That statement is patronizing, do you think if you don't have a set # of posts your a "noob"
2.I never post unless I know somewhat the subject being discussed
3.I usually have documentation to back-up my facts

Thanks
a c 172 U Graphics card
September 28, 2007 6:15:55 AM

No math to back up your statements huh? I didn't say you are a noob, just someone who is confused about things. I don't know why you are acting this way, but unless you can accept the fact that you might possibly be wrong, you aren't going to learn how/why you are wrong. If you're willing, read the rest of this post. If you are so sure you're right, either back up your claim with evidence, or show me where I made a mistake with my math. (seeing as you haven't done that yet, I'm assuming my math is right.)

Lets review. Each rail can output a certain amount of power. In the case of the SP 450W, the first 12V rail can output a MAXIMUM of 15A, while the second can do a MAXIMUM of 17A. Some people mistakenly believe that you can add these two number together to get the total amount of power for the 12V rails. (or in your case, 18A + 18A) The problem with this is that those are the individual rails, not the total amount of power for the PSU overall. The SP 450W can't output 15A + 17A on the 12V rail at the same time, but in fact 24A. Lets look at a good example. Click on this link, then the third picture.

http://www.newegg.com/Product/Product.aspx?Item=N82E168...

This PSU has four 12V rails that individually can output a max of 18A. If you follow the mistaken logic, you would think this PSU could output 864W combined for the 12V rail. (18A * 4 rails = 72A. 72A * 12V = 864W. See how I proved this with math?) Antec doesn't claim that this psu can output a COMBINED wattage that is that high. They say that the combined output for ALL 12V lines is 768W. 768W / 12V = 64A. This means that the circuitry inside the PSU can't supply enough power to feed the maximum that each rail is capable of. If divided equally, each 12V rail could have 16A. (in actuality each rail would probably be different. The motherboard rail might be 10A, the CPU rail might be 15A, the GPU rail might be 18A, while the fourth rail might be at 8A.)

Some PSU manufacturers don't make it easy to figure out how much power the PSU can output. They might list peak power instead of sustained. They might just list each rail and the amperage, with no total figures. These are the power supplies you should avoid.

I'm not claiming that you misread your label. I don't doubt that it said 18A under both rails. But to write what you did, "18A + 18a = 264w maximum combined wattage on the 12v rails" is wrong. 18A + 18A = 36A. 264W / 12V does equal 22A. 18A maximum for each line, but combined, it could only do 22A. (either 18A on one with 4A on the other, or 11A on both, or any number of possible configurations.)

I hope this makes sense.

September 28, 2007 6:31:41 AM

2nd thought, tell me I'm wrong again.
a c 172 U Graphics card
September 28, 2007 6:45:12 AM

Whats confusing about individual and combined? 18A individual, 22A max output for both rails combined. That PSU will not output 36A. (18A + 18A = 36A) What are you not understanding?


EDIT: Hey Cleeve, I think he might be to pissed at me. Can you explain why 18A + 18A can't equal 264W?
September 28, 2007 6:58:27 AM

a picture's worth a thousand words
October 14, 2007 6:08:28 PM

Hi!
I have to admit, I've been building systems for a long time but I'm also confused about multirail power supplies. I recently bought a Crosair HX620 PSU. The total wattage available on to the 12v rails is 600w. There are three rails that advertize a max of 18a each. Now, if my math is correct, that gives me 16.6a available on each of the combined rails, correct? (600/12=50. 50/3=16.6)? This PSU also "shares" power among the rails but to what extent, I don't know.
Thing is, I'm looking at a Diamond Radeon x1950 Pro card that says it needs 30a max on a single 12v rail. By my math, I could use two rails and get max of 33.2a, correct?
Thanks for any help anyone can give me here. :) 
a c 172 U Graphics card
October 14, 2007 6:19:42 PM

Double check what it says about that x1950pro. I would be very surprised if it actually says it needs 30A on a single rail. First, the ATX specs say your not supposed to output more then 20(?)A on a single rail, so they would be asking you to run something that violates ATX specs.

Second, every time I've looked at the x1950 series cards, they say you need 30A on the 12V rails. Not on one, but all. It usually says something like "assuming a fully loaded system". Trust me, the Corsair 620 has plenty of power to run that card. (I would even be willing to bet that the Corsair 520W would have enough power to run the x1950.)
October 14, 2007 8:47:23 PM

4745454b said:
Whats confusing about individual and combined? 18A individual, 22A max output for both rails combined. That PSU will not output 36A. (18A + 18A = 36A) What are you not understanding?


EDIT: Hey Cleeve, I think he might be to pissed at me. Can you explain why 18A + 18A can't equal 264W?

See the link in my signature
a b U Graphics card
October 14, 2007 9:28:06 PM

4745454b said:
Double check what it says about that x1950pro. I would be very surprised if it actually says it needs 30A on a single rail. First, the ATX specs say your not supposed to output more then 20(?)A on a single rail, so they would be asking you to run something that violates ATX specs.

Second, every time I've looked at the x1950 series cards, they say you need 30A on the 12V rails. Not on one, but all. It usually says something like "assuming a fully loaded system". Trust me, the Corsair 620 has plenty of power to run that card. (I would even be willing to bet that the Corsair 520W would have enough power to run the x1950.)

Even the 450w Corsair can do it. Look at my link below, that states that you can power a e6600 OC'd and a 8800gtx.

8800gtx on 380w Antec PSU!
http://www.overclockers.com/articles1452/

When you use a QUALITY PSU, you usually have solid and efficient power. Here is another link for PSU information. I'll type it out, because the link to the forum has been banned.
PSU 101 information
http://www.***.com/forums/cases-psus/109-psu-selection-guide-psu-101-102-a.html
Where the ***** are subsitute it for (x-c-p-u-s) don't include the "-'s" in the link.

Generally you take the available power for the 12v1,12v2,12v3, 12v4, 12vxxxx, etc. and divide that by 12v to get the available Amps on the 12v rails. Example: 360w combined on all 12v rails divided by 12v = 30 amps total. So if you had 18A on 2 rails and your total Watts was 360w you would have 30 amps total. Again if you had 360w total for 4 12v rails than you would still have 30amps total. Do you see what I'm talking about?
a b U Graphics card
October 14, 2007 9:38:50 PM

gtcroatan said:
Hi!
I have to admit, I've been building systems for a long time but I'm also confused about multirail power supplies. I recently bought a Crosair HX620 PSU. The total wattage available on to the 12v rails is 600w. There are three rails that advertize a max of 18a each. Now, if my math is correct, that gives me 16.6a available on each of the combined rails, correct? (600/12=50. 50/3=16.6)? This PSU also "shares" power among the rails but to what extent, I don't know.
Thing is, I'm looking at a Diamond Radeon x1950 Pro card that says it needs 30a max on a single 12v rail. By my math, I could use two rails and get max of 33.2a, correct?
Thanks for any help anyone can give me here. :) 

Look at this link to clarify things for you.
http://www.zipzoomfly.com/PDF/373110.pdf

The 620 psu has 600w on combined 12v rails, so you would have 600w/12v= 50 amps!!
The 520 psu has 480w on combined 12v rails, so you would have 480w/12v= 40 amps!!

Hopefully that link and explanation has helped you understand how one can come up with the amperage on the 12v rails.
a b U Graphics card
October 14, 2007 10:35:04 PM

Johnny wrote:"Now, I tried to bump my system a few percentiles up from stalk but the system just reboots and I get the 3 sec beep and no post!" Not entirely accurate. You are completing the POST - just unsuccessfully.

First, about the original problem: If the Foxconn uses the Award BIOS, a series of single 3 second long beeps indicates a memory problem. Run memtest. You may need to increase the memory voltage or relax the memory timing. That would explain why your system works at stock speeds, fails when OC'ed, and starts working after you reset the BIOS back to stock speeds.The memory subsystem is fed by the 3.3 volt PSU output.

Power consumption of 7950? I don't know - not going there, people are starting to get rude here. I learned a long time ago (back when the world was young and snakes walked the earth) that attacking ideas is OK, but personal attacks are counterproductive.

4745454b is correct about PSU capacity. For another example, I have an 650 w Antec TP3 in Box #1. That's a total capacity of 650 watts. It has three 12 volt rails rated at a maximum of 19 amps each (684 watts total). Obviously, all 3 rails cannot simultaneously operate at maximum current. Data on the box says 12 volt max output is 52 amps (624 watts). That will work, but it's impractical because it leaves just 24 watts to run everything else.

I do not know which power cables (main connector, the 4 or 8 pin EPS connectors, the 6 pin GPU connectors, or the drive connectors) are tied to which rail. This is the second time that this question has come up, and now I am curious enough to open up the box and pull the PSU to find out. Unfortunately, my DMM is at work, and I am on a forced vacation until next week.

If you are curious, bookmark this thread and I will post what I discover next week.
October 15, 2007 12:32:37 AM

Great! Thanks for the help! I did a LOT of homework before I bought this last PSU. :D 
BTW, the card I'm thinking of buying has two large Molex connectors. Would there be anything wrong with connecting two seperate rails to the two connectors? There's a map at the Corsair site that show which plugs go to each rail.
Thanks again!
MC
:) 
a b U Graphics card
October 15, 2007 2:33:57 AM

gtcroatan said:
Great! Thanks for the help! I did a LOT of homework before I bought this last PSU. :D 
BTW, the card I'm thinking of buying has two large Molex connectors. Would there be anything wrong with connecting two seperate rails to the two connectors? There's a map at the Corsair site that show which plugs go to each rail.
Thanks again!
MC
:) 

Being an electronic technician, I would say that would be a smart idea, since you'd be splitting the load over the 2 different rails (if they are different circuits of coarse).
October 15, 2007 3:38:21 PM

johnnyq1233 said:
I've checked out the bfg site on my 7950gt/oc 512..
They say I should have 22+ amps on the +12v rail.
My current supply is only giving 17A but my system runs stable.
Now, I tried to bump my system a few percentiles up from stalk but the system just reboots and I get the 3 sec
beep and no post!
Should I invest in a better psu?
The psu I'm using is an ANTEC SMARTPOWER 450....

ps. I think this might be causing some frame rate dropage as well...



Just get another power supply for christ sakes .... it's a low priced fix and easy as the devil to do . Then if you're running any other addons that draw power the system will handle it . You never said if you have any aux. non powered drives or units added to your system that could be using power .... but that way if you do in the future it will handle them with ease . Why go through the headaches and underpowering your computer and spending hours upon hours of frustration ???? ----- :pt1cable: 
a c 172 U Graphics card
October 15, 2007 5:59:40 PM

It might be "cheap" to buy, but it might not solve the problem. If you remember, the problem was that he couldn't use an auto overclock found on his motherboard that overclocked his system by 20%. If you re-read my posts, I told him that he should try to manually overclock as the auto settings might not have enough voltage or have some other problem. Before deciding that it is the PSU and buying another, I would make an attempt at doing it manually to see if you can get the results you want.

The SP450W isn't the best PSU, but it isn't the worst one by any stretch.
a b U Graphics card
October 20, 2007 3:55:48 PM

Reference to Oct. 15 post:
OK. It's Saturday, the beginning of my work week. I disconnected all of the PSU cables. I started by assuming that I would read, at the worst, a low resistance between the 12 volt cables from any two rails. To make a long story short, any 12 volt line from any power cable to any other read a short. Then I pulled the PSU and opened it up. I found three groups of wires going to printed circuit board pads labeled 12V1, 12V2, and 12V3. There, I read 0 ohms between any two pads.

So I don't know what's going on inside the PSU. I figured that if the box says 3 rails, I should find find some separation between them.

I found an Australian site: http://www.atomicmpc.com.au/forums.asp?s=2&c=7&t=9354&p... , that lists the power consumption of a wide range of video cards. They also link to their source of the data.
!