Will this PSU support a 9800GT?

tknick90 said:
Yeah it should be fine.
Click to expand...

No definately not. It is not about the wattage and I am assuming you guys just added the two 12V rails? You cannot do that.

Why? Because under ATX 2.2 design standards of that PSU, 12V+2 is dedicated to the CPU. This effectively traps the unused current on that rail, making it unusable to the rest of the system. Let me explain.

If the 12-volt rail that powers (dedicated) the CPU is rated for 18 amps and the CPU only uses 7A, the remaining 11A is unusable, since it is isolated from the rest of the system (under the above mentioned standard). That means that you only have 20A (i.e. 12V+1) for the rest of the system. You need 26A minimum available for a system with a 9800GT. That PSU is poor quality in every way, and cannot provide sufficient power to your system with a 9800GT or a quad core.

Now before i get flamed, it will probably work, but it won't for long, and it when it goes it can take out other components of your system. I highly recommend a quality PSU, such as the 620W Corsair for your system (which is not limited to the above due to its EPS 2.91 standard), which will take the 9800GT and a quad in the future.
 
Last edited:
bigfellla said:
No definately not. It is not about the wattage and I am assuming you guys just added the two 12V rails? You cannot do that.

Why? Because under ATX 2.2 design standards of that PSU, 12V+2 is dedicated to the CPU. This effectively traps the unused current on that rail, making it unusable to the rest of the system. Let me explain.

If the 12-volt rail that powers (dedicated) the CPU is rated for 18 amps and the CPU only uses 7A, the remaining 11A is unusable, since it is isolated from the rest of the system (under the above mentioned standard).
Click to expand...

Thats only 50% right. Lets take one I have. Its a 550 watt with two 12V rails at 20 amps each. It has a total of 38 amps on the 12V rails.

You dont just add the two 12V rail together and say it has 40 amps total. You can get a rough amount dividing by 12 of the total amount of watts on the 12V rails, not the total of the P/S. Thats why this one only has 38 total even though it has two 20 amp rails.

Another point. Its true that most power supplies have one of the rails dedicated to the CPU. But that does not mean that all of the amps on that rail is held.

Take the above P/S in the example, if one rail is the CPU rail it does not hold the whole 20 amps on that one rail and just leaves 18 amps for the other. (All a dedicated CPU rail means is that no other Device/hardware can pull off that rail), not that the rail holds anything. Its true that both rails do have a minimal amount of amps that is held but its somewhere around 3 to 6 amps on each rail, depending one brand and model. The ratings on the rail is just the (max) any one rail can pull. But the CPU rail does not hold the max amps rating of that rail and just leaves whats left over for the second rail. It doesnt work that way. The rating on the rail is just the most the rail can pull, its not the amount held on the rail.

Now there are upper end P/S that (really) have dedicated rails and your example would be true to a point. But in the example no rail is pulling off each other so nothing is just left over for the other, they never pull off each other. But the above cheap P/S is not one.
 
Last edited:
StrangleHold said:
Thats only 50% right. Lets take one I have. Its a 550 watt with two 12V rails at 20 amps each. It has a total of 38 amps on the 12V rails.

You dont just add the two 12V rail together and say it has 40 amps total. You can get a rough amount dividing by 12 of the total amount of watts on the 12V rails, not the total of the P/S. Thats why this one only has 38 total even though it has two 20 amp rails.

Another point. Its true that most power supplies have one of the rails dedicated to the CPU. But that does not mean that all of the amps on that rail is held.

Take the above P/S in the example, if one rail is the CPU rail it does not hold the whole 20 amps on that one rail and just leaves 18 amps for the other. (All a dedicated CPU rail means is that no other Device/hardware can pull off that rail), not that the rail holds anything. Its true that both rails do have a minimal amount of amps that is held but its somewhere around 3 to 6 amps on each rail, depending one brand and model. The ratings on the rail is just the (max) any one rail can pull. But the CPU rail does not hold the max amps rating of that rail and just leaves whats left over for the second rail. It doesnt work that way. The rating on the rail is just the most the rail can pull, its not the amount held on the rail.

Now there are upper end P/S that (really) have dedicated rails and your example would be true to a point. But in the example no rail is pulling off each other so nothing is just left over for the other, they never pull off each other. But the above cheap P/S is not one.
Click to expand...

That's only 0% right, Strangle, thanks for your response, but you are misguided here man and you need to do your research.

If you took the time to read the ATX 2.2 standard you will realise that i am 100% right. Without EPS 2.91 cert., there nothing that i have said regarding that PSU that is false.

I never said you add the 12V rails together nor do you just simply take the wattage and divide by 12V because under ATX standards 2.2, the CPU rail is isolated (unless it is EPS certified which this PSU is not) from the rest of the system, meaning that power capacity cannot be shared. Read the standard if you don't believe me. A PSU requires ATX 2.2 and EPS 2.91 to behave in the manner you refer to. This PSU does not have that certification.

PC Power and Cooling back this up with the following statement regarding 12V rails with ATX 240VAC limitations: "...losses occur because power literally gets "trapped" on under-utilized rails." This is essentially why quality brands are moving towards single high amperage rails again.

If anything else is missing from my post, please state concisely what parts of my response are incorrect, as i cannot see any that are, and with respect (i know you are a well respected member of this forum) but your response was a bit hard to follow mate. :) :D
 
Last edited:
bigfellla said:
Why? Because under ATX 2.2 design standards of that PSU, 12V+2 is dedicated to the CPU. This effectively traps the unused current on that rail, making it unusable to the rest of the system. Let me explain.

If the 12-volt rail that powers (dedicated) the CPU is rated for 18 amps and the CPU only uses 7A, the remaining 11A is unusable, since it is isolated from the rest of the system
Click to expand...

This is where you are wrong.

The max rating on the rails even the CPU rail is not whats held on the rail. If the CPU rail is rated at 18 amps max, it is not holding 18 amps. True it has a certain amount of amps that is held, buts its not the max rating on the rail. I have no idea where you get that, maybe because you think it is so makes it so! But its not. The CPU rail does hold a certain amount of amps that is unusable to the other rails, but its not the max amount that the rail is rated for.
 
no, you need ~28a on the second rail for an 9800. Thats why most companies are moving back from multiple rails to single rail designs

bigfella is right about the 1st rail being dedicated to the CPU. Dont agree with what he said about it holding the current (it just draws as much as is needed, thats electronics 101), but thats not relevant.
 
StrangleHold said:
This is where you are wrong.

...I have no idea where you get that, maybe because you think it is so makes it so! But its not. The CPU rail does hold a certain amount of amps that is unusable to the other rails, but its not the max amount that the rail is rated for.
Click to expand...

No, I am afraid it is you that is wrong, and clearly you haven't read the standard. I never said hold (as in storage), but I did use the word isolate, as in separate from. A PSU that is designed to ATX 2.2 (without EPS 2.91) such as the PSU in question in this thread shall under "Section 1.2.3 Separate current limit for 12V2 on the 2x2 connector":

"The 12V rail on the 2 x 2 power connector should be a separate current limited output to meet the requirements of UL and EN 60950." ATX12V
Power Supply Design Guide, Version 2.2, March 2005, pp 9.

You can also cross reference this if you wish IEC 60950, 3rd ed., 1999, which is equivalent to the EN 60950: 2000 or the Canadian Standard UL* 60950, 3rd Edition –CAN/CSA-C22.2-60950-00.

Now that we agree it is a separate 12V rail for the CPU (i.e. 12V+2 isolated), we can remove this rail from our considerations, because it cannot, under this standard alone, share its capacity to deliver any current. That leaves whatever rails are left over, in this case one 20A rail (maximum possible under the standard due to 240VAC safety), and this clearly cannot provide sufficient power for the system in question (e.g. minimum of 26A).

If you still think I am wrong Stangle, you should tell PC Power and Cooling (not to mention the ATX standards) to update their documents as they clearly agree with me in this concise explanation: http://www.pcpower.com/technology/myths/#m8
 
Last edited:
bigfellla said:
Now that we agree it is a separate 12V rail for the CPU (i.e. 12V+2 isolated), we can remove this rail from our considerations, because it cannot, under this standard alone, share its capacity to deliver any current. That leaves whatever rails are left over, in this case one 20A rail (maximum possible under the standard due to 240VAC safety), and this clearly cannot provide sufficient power for the system in question (e.g. minimum of 26A).
Click to expand...

I cut the top and bottom part for repetitiveness that does not prove what you said.

What your trying to dodge is that you cant claim that just because a P/S has a max rating of 20 or however many it states (max) pull of amps on the 12V CPU rail is the amount that the rail holds. There is a max and a minimum that any rail can carry and hold (CPU rail included). What is stated on the P/S is the max. The minimum is what is held and not shared with other rails.

Just because the P/S has a stated (max) pull of 20 amps on the CPU rail does not mean that is the amount of amps held on that rail. You keep dodging the issue, I agree that there are amps held on the CPU rail, but its not whatever they claim is the max of the CPU rail can pull.
 
Last edited:
jdbennet said:
bigfella is right about the 1st rail being dedicated to the CPU. Dont agree with what he said about it holding the current (it just draws as much as is needed, thats electronics 101), but thats not relevant.
Click to expand...

I agree that the CPU rail hold amps. But its not the stated (max) amps that is listed on the CPU 12V rail that big keeps going on about.

But I do agree on the P/S dazzeerr asked about. I would not buy it or recommend it.
 
Last edited:
Of course this proves something, it is FROM THE STANDARD!!?? It’s not repetitive; it’s a reference from the actual ATX2.2 standard that the PSU in question was designed against. I never said hold (as in storage), but I did use the word isolate, as in separate from. Definition of separate: "...independent; not united or joint".

One more time and then I give up:

A PSU that is designed to ATX 2.2 (without EPS 2.91) such as the PSU in question in this thread shall under "Section 1.2.3 Separate current limit for 12V2 on the 2x2 connector":

"The 12V rail on the 2 x 2 power connector should be a separate current limited output to meet the requirements of UL and EN 60950." ATX12V
Power Supply Design Guide, Version 2.2, March 2005, pp 9.

and... PC Power and Cooling.

"...multi-rail 12-volt design has distribution losses of up to 30% of the power supply's rating. Those losses occur because power literally gets "trapped" on under-utilized rails. For example, if the 12-volt rail that powers the CPU is rated for 17 amps and the CPU only uses 7A, the remaining 10A is unusable, since it is isolated from the rest of the system."

  • The 12V+2 rail is SEPERATE, and cannot share any underutilised capacity. This is the point.
  • The remaining rail is 240VAC limited meaning it cannot deliver more than 20A, which in addition to the above is insufficient.


These are fairly clear points backed up by what I would consider very solid references, maybe Strangle if you are right and the standard is wrong and PC Power and Cooling are wrong, you should update their documents for them.
 
Last edited:
That proves nothing, your claiming that the (MAX) rating for the CPU rail on the supply was held, isolate- separate whatever word you want to use. Its not, its the minimum thats held and is usually not even listed on the P/S. All the rails have a minimum thats held. The CPU rail is higher because of the standard but you cant just subtract what ever the P/S maker decides to set as the rails max amps on the CPU 12V from the rest.
 
Whatever, lol, the entire rail is isolated. Period. And, it is not me that is claiming this, its THE ATX STANDARD backed up by PC POWER AND COOLING.

Anyway, lets not argue, you can believe what you want, but I give up.
 
Last edited:
This is a quote from a site, now I'm only reading this thread from an interest point of view and ONLY want to know the real answer. The way I read it is the whole rail is unusable, right or wrong, or is the sites quote wrong?

For example, if the 12-volt rail that powers the CPU is rated for 17 amps and the CPU only uses 7A, the remaining 10A is unusable, since it is isolated from the rest of the system.
Click to expand...

Don't get at me as I'm not sure :)
 
TFT said:
This is a quote from a site, now I'm only reading this thread from an interest point of view and ONLY want to know the real answer. The way I read it is the whole rail is unusable, right or wrong, or is the sites quote wrong?



Don't get at me as I'm not sure :)
Click to expand...

Finally someone who can understand, plus the ATX standard is quite clear. I don't think i am misunderstanding what Strangle is saying, because as i understand it he thinks that I am saying there is some kind of power being held, im not saying that, i am saying according to the standards outlined previously, the rail is isolated and unavailable.
 
Last edited:
flame0247 said:
dam. forget this complicated stuff, just buy a 700w Crosair
Click to expand...

Thank you. It's not ****ing rocket science. Buy a quality unit and enjoy it. :rolleyes:

Newegg has an awesome PC Power & Cooling promotion that runs through the 26th.

http://www.newegg.com/Product/Produ...N=2010320058 50009830&name=PC Power & Cooling

Pay special attention to the line above each unit that states: Get an additional 20% off w/promo code "pcpc20", ends 9/26. I've owned the 750W Quad Silencer for over a year. It's powered dual 8800 Ultras, a Radeon 3870X2, etc. If you have the money, get one of these units and ignore the minutia discussed in this thread. ;)

For what you need, I recommend this 500W unit. $68.63 shipped. The 9800 GT requires 400W w/ 26 amps supporting the +12V rail. This unit is more than adequate. :)
 
Last edited:
You must log in or register to reply here.
Back
Top