Volts vs Amps for power supply specs. What's the importance to power a video card?

[Petros_k]

Trying to understand the volts required for a specific AGP video card to see if my existing power supply might be too low to run the card. There are 2 cards that I'm interested in: a GeForce FX 5500, and a GeForce FX 6200. I'm not so interested in the recommended watts for a power supply unit. When I go to the specs for these two cards, this is what's recommended:

"Minimum recommended power supply with +12 Volt current rating of 18 Amp."

I know the specs for the existing power supply in my computer indicates the following:

+3.3V@15A
+5V@11A
+12V@5A
+12.8V@7.5A
-12V@0.15A
+5VSB@3A

If I don't have a power supply that indicates at least a +12V current rating of 18 amps, the video card won't work? What is the real significance of recommended amps?

I'm concerned for a few reasons, but mostly because I have a proprietary power supply unit that will be very tough to replace.

 

[zir_blazer]

Remember than those 18A on the 12V line is for the entire machine, the Video Card doesn't draws 216W by itself. nVidia an ATI usually likes to recommend you Watts/Ampers for an entire computer, not what the Video Card really needs. Depending on the rest of the computer, that value may be WAY higher than it should. So the other components that are connected there are also important.

Are you sure than its 12.8V and not 12V2 or something like that? It could be a second 12V rail (Dual Rail Power Supply). 12.8V is not even a valid value.

 

[thedosbox]

Power consumption is measured in Watts = V * A. A power supply that cannot handle the load being demanded of it could result in system shutdown, or random crashes.

In theory, that PSU can deliver 60W on the first 12V rail, and 90W on the second (assuming you meant 12V). However, reality might be somewhat different as you'd need to factor in age and the maximum combined 12V capacity.

As for the power requirements of those cards in particular - no idea. They don't have external power connectors, so it's not going to be much. The complicating factor is that the AGP slot can provide power over 3.3V, 5V or 12V.

 

[lehtv]

By the looks of it, your PSU is a very old design with only a maximum of 12.5A available on the +12V, probably less because the combined +12V capacity is typically lower than the sum of the +12V rail amperages. Both of the AGP cards you posted require a significant amount of power, and in terms of power consumption would not be classified as "low end" by today's standards even though they certainly perform extremely poorly.

What is the real significance of recommended amps?

To ensure you don't overload the unit and cause it or and/or your PC to malfunction.

 

[Petros_k]

The power supply unit in my system, which is an old Compaq EVO D310 (quickspecs here: http://h18002.www1.hp.com/products/...html#spectype=worldwide&type=html&docid=11348 ) has a power supply that has the above specs on a label on the unit itself. You can see it here: http://www.atlantisgadgets.com/index.php?main_page=product_info&cPath=5_10&products_id=100 Look at the last number listed. It's +12.8V.

This was a proprietary power supply unit made specifically for Compaq more than 10 years ago. Its form factor is not typical ATX. The unit was made to fit in what Compaq called a "micro-tower." I've been told that many of the typical PSUs people buy today for a cheap upgrade will not work with the motherboard of this system, and they also will not fit because the case is not typical ATX. But I digress...

zir blazer: You say "those 18A on the 12V line is for the entire machine." So then it's possible if my system is not overloaded the 18A for the 12V line is not going to be an issue? I thought the amps in this recommendation were somehow pertaining to what's needed for only the voltage going to the card. I don't know the difference between volts vs. amps (but I do understand watts), hence my initial question.


Can't anybody give me a straight answer on this? You see the spec above that's the label on the power supply unit itself. I'm seeing a recommendation for voltage and amps that says: ""Minimum recommended power supply with +12 Volt current rating of 18 Amp."

What do I have to know about my system to know if the video cards mentioned above will be able to run or not? Please don't tell me I have to become an electrical engineer

 

[heymrdj]

Just a note guys that being he's looking for AGP he's most likely talking about an old Compaq. Those had proprietary PSU's with 12 and 12.8v rails. They were distinct and not interchangeable.

http://denihow.com/what-is-the-12-8v-rail-on-my-psu/

 

[thedosbox]

Yeah, I wouldn't try using anything other than integrated video on that thing.

 

[heymrdj]

A FX6200 needs 50-60 watts of power. On those setups 12.8v is 100% dedicated to the cpu and subsystem. The 12v runs the drives and some of the subsystem. Realistically you'll have at best 5A of 12v available. Those PSU's were simply built to run forever with just enough power to run the system. While your mileage may vary (many were overbuilt), generally they were never designed to support upgraded graphics, and it's very unlikely any card other than a basic pci one (that uses a floppy cable for power) will run.

 

[Petros_k]

Power consumption is measured in Watts = V * A.

Just this alone doesn't seem right to me if the 18 amps is what's needed for only the card to run. If you go here:

http://forums.atomicmpc.com.au/index.php?showtopic=264

And look down the long list for these two video cards, you will see that they each don't draw more power than 26 watts at PEAK.

 

[Petros_k]

A FX6200 needs 50-60 watts of power.

Not according to this website:

http://forums.atomicmpc.com.au/index.php?showtopic=264

Where are you getting your specs from?

 

[Petros_k]

The 12v runs the drives and some of the subsystem. Realistically you'll have at best 5A of 12v available. Those PSU's were simply built to run forever with just enough power to run the system. While your mileage may vary (many were overbuilt), generally they were never designed to support upgraded graphics, and it's very unlikely any card other than a basic pci one (that uses a floppy cable for power) will run.

Again, not quite right. If you look at the quickspecs for the EVO D310 (link is above) you can see the unit was available with these after-market AGP video cards:

Intel DVI AGP Digital Display (ADD) Card 283016-B21
NVIDIA GeForce2 MX400 32-MB DDRAM AGP 309055-B21
NVIDIA GeForce2 MX200 64-MB with DVI-I 283051-B21
NVIDIA GeForce2 MX420 64-MB DDRAM with VGA and Svideo 301087-B21


Plus, it makes absolutely no sense that the motherboard for the system has 3 PCI slots and an AGP slot but Compaq required users to upgrade to some other power supply unit just to use them. There was no other PSU available from Compaq at the time.


Are you guys really telling me that:

A. There's no way to interpret the recommendation of "Minimum recommended power supply with +12 Volt current rating of 18 Amp" as it pertains to my system?

B. There's no way to assess before actual installation if the two low-watt and low-end video cards will work in the AGP slot?

 

[thedosbox]

Just this alone doesn't seem right to me if the 18 amps is what's needed for only the card to run.

zir_blazer is correct in that video card manufacturers specify power requirements for the entire system, not the card alone. And it's true that they often inflate those requirements under the assumption someone has a crappy PSU.

http://forums.atomicmpc.com.au/index.php?showtopic=264

And look down the long list for these two video cards, you will see that they each don't draw more power than 26 watts at PEAK.

As that link notes, the AGP slot can deliver up to 42W of power, of which a maximum of 1A (12W) can come from the 12V rail, so you may well be right. You appear to have plenty of 3V & 5V capacity, so it might be OK.

Emphasis on "might".

While I wouldn't risk it, it's your system, not mine.

 

[Petros_k]

Realistically you'll have at best 5A of 12v available.

But what does this mean if there's apparently a recommendation for the two video cards that says: "Minimum recommended power supply with +12 Volt current rating of 18 Amp" ?? Doe sit mean that if I pulled out all the drives from my system and ran only the motherboard, the CPU, and a monitor I would not be able to get the video card to work? Or are you saying GIVEN the other devices installed on my system will require power there might not be enough for the whole system to run? The latter is not really what I'm asking because that's a function of the total watts required for my system.

Again, I was asking specifically about AMPS and how the spec quoted above will possible mean the video card will not work if the specs on my power supply unit are as indicated in my first post.

I have no illusions about the original power supply unit being quite "puny" according to today's standards. I reiterate: The two cards do not require more than 26 watts of power each, and I am NOT using the card to do 3D graphics or for gaming.

 

[heymrdj]

Again, not quite right. If you look at the quickspecs for the EVO D310 (link is above) you can see the unit was available with these after-market AGP video cards:

Intel DVI AGP Digital Display (ADD) Card 283016-B21
NVIDIA GeForce2 MX400 32-MB DDRAM AGP 309055-B21
NVIDIA GeForce2 MX200 64-MB with DVI-I 283051-B21
NVIDIA GeForce2 MX420 64-MB DDRAM with VGA and Svideo 301087-B21


Plus, it makes absolutely no sense that the motherboard for the system has 3 PCI slots and an AGP slot but Compaq required users to upgrade to some other power supply unit just to use them. There was no other PSU available from Compaq at the time.


Are you guys really telling me that:

A. There's no way to interpret the recommendation of "Minimum recommended power supply with +12 Volt current rating of 18 Amp" as it pertains to my system?

B. There's no way to assess before actual installation if the two low-watt and low-end video cards will work in the AGP slot?

Ok lets dispel the FUD. First of all your link has low data quality. For goodness sake the 5200 had 1 user with who only measured supposed peak power, with nothing else to show. My data was calculated from multiple sources extrapolating changes in system power vs available card power. The math isn't too hard.

A. no there's not, because the types of 12v don't go to one place, Compaq did it proprietarily.

B. AGP is how Compaq got it done. The 12.8v line feeds the AGP slot, which can feed 40W of power. The big IF is how the particular card you buy is wired. If it's wired to pull power from AGP mainly, and sparingly use the molex, you can keep from overdrawing that last 3-5A you have free on the 12v rail. If not, or if you use PCI, it doesn't stand a chance. This is why the EVO could use lowly MX cards. If you hadn't read much on the cards of yesteryear, you'll find that MX and FX cards are generationally very different, the former designed when 5v rails were large and 12v was small, and the latter designed when specs started weighing in favor of 12v rails.

http://en.wikipedia.org/wiki/AGP#Power_consumption

 

[Petros_k]

As that link notes, the AGP slot can deliver up to 42W of power, of which a maximum of 1A (12W) can come from the 12V rail, so you may well be right. You appear to have plenty of 3V & 5V capacity, so it might be OK.

Emphasis on "might".

What do I need to do (besides actually installing the card) to estimate if this recommendation: "Minimum recommended power supply with +12 Volt current rating of 18 Amp" is going to make it impossible to run one of the two AGP video cards mentioned above?

 

[thedosbox]

Are you guys really telling me that:

A. There's no way to interpret the recommendation of "Minimum recommended power supply with +12 Volt current rating of 18 Amp" as it pertains to my system?

That recommendation is meaningless for the reason given above - namely it's to cover the manufacturers ass.

 

[zir_blazer]

zir blazer: You say "those 18A on the 12V line is for the entire machine." So then it's possible if my system is not overloaded the 18A for the 12V line is not going to be an issue? I thought the amps in this recommendation were somehow pertaining to what's needed for only the voltage going to the card. I don't know the difference between volts vs. amps (but I do understand watts), hence my initial question.

Basically, those 18A is what the Video Card manufacturers recommends in a Power Supply for the ENTIRE machine, not for the Video Card itself. For that reason these recommendations are usually misleading, they usually tell you a much bigger number that what you actually need. If you know the actual power consumption of the Video Card that you want and your system components, you can get a more accurate number that is always lower than that.

To put it simply, Power Supply usually has multiple rails that can supply different Voltages (Standard is 3.3V, 5V and 12V) with a maximum capacity given for each of them given in Ampers. Watts is equal to Voltage * Ampers, so the higher the Ampers, the higher the Watts. Problem is that depending on the ATX standard that these Power Supplies were designed around, may priorize more 3.3V and 5V than 12V, that is what current machines uses the most. So a 500W Power Supply based on an old ATX standard from 10 years ago may have very little Ampers on 12V and thus useless for feeding any modern computer, as from a decade ago or so, most of what a modern computer uses comes from the 12V rail.


However, in your particular case, considering that you have an OEM computer with a propietary Power Supply, I would simply save money and try to purchase a new one that trying to upgrade that one.

 

[Petros_k]

Ok lets dispel the FUD.

FUD ?

B. AGP is how Compaq got it done. The 12.8v line feeds the AGP slot, which can feed 40W of power. The big IF is how the particular card you buy is wired. If it's wired to pull power from AGP mainly, and sparingly use the molex, you can keep from overdrawing that last 3-5A you have free on the 12v rail.

The two cards listed here only draw power from the AGP slot. They have no other connectors needed (certainly not Molex).

If not, or if you use PCI, it doesn't stand a chance.

What do you mean? If I use a PCI slot in addition to a video card? Or, do you mean if I try using a PCI video card?

This is why the EVO could use lowly MX cards. If you hadn't read much on the cards of yesteryear, you'll find that MX and FX cards are generationally very different, the former designed when 5v rails were large and 12v was small, and the latter designed when specs started weighing in favor of 12v rails.

If the power consumption of MX cards is something like 10 watts max, and the power consumption of FX cards is something like 26 watts max., And I have more than 26 watts of power avaiable given all the devices installed on my system, of what significance is the recommended 18 amps?


*Please be careful. I'm not trying to argue with anyone. I'm trying to focus on one thing here that makes no sense to me, and it's in this recommendation of "Minimum recommended power supply with +12 Volt current rating of 18 Amp," and I'm concerned where they are getting the 18 amp part of it from. It looks to me like the PSU needs to have an available "rail" (if that's the right term) of 12V@18amps, and if you look at my first post the label on the PSU doesn't have this.

And I do appreciate the replies. Thanks.

 

[VirtualLarry]

The short of it - I don't think that it is going to work.

 

[heymrdj]

FUD ?

The link for your wattage evidence (where you're quoting the wattages) has no proof of data. There's no review, no testing unit, nothing. Hence why I referenced it as FUD. I personally find their numbers low.

The two cards listed here only draw power from the AGP slot. They have no other connectors needed (certainly not Molex).

My 6 series uses a 4 pin. Maybe not all the 6 series do, my mistake.

What do you mean? If I use a PCI slot in addition to a video card? Or, do you mean if I try using a PCI video card?

Yes, PCI has a 25W limit, and other than the high binned (high quality, low leakage) 6200's, all the rest need 4 pins, which puts more load on that very tiny 12v rail you have. The goal is to pull through AGP so that the wattage can come from 12.8V


If the power consumption of MX cards is something like 10 watts max, and the power consumption of FX cards is something like 26 watts max., And I have more than 26 watts of power avaiable given all the devices installed on my system, of what significance is the recommended 18 amps?


The significance is system stability. As mentioned, the recommendation was simply not written for your computer. You're stuck with a system that splits an odd rail and a normal rail. This would be easy if the 12.8 ran the system board and the 12 ran the rest of the system, but it doesn't, the 12 runs the system too. It's kind of like trying to accurately measure power on a prius. You have a gas engine plus an electric engine, say 75 hp and 50hp respectively (not accurate but I can't wiki it right now). The total rated power, however, is 100hp. Why? Because while the gas engine is running the wheels, it's also turning a generator that's feeding the electric motor which in turn is also driving the wheels. You can't count the power twice. So 75+50=100. This is the same way. You have 12.8 to system. You have 12 to system plus peripherals. We didn't design it, so none of us can say where that other 12v rail is actually going (is it an area that's currently unused on your mainboard? Is it the only thing feeding 12v to the processor's regulator? Two opposite possibilities there.

*Please be careful. I'm not trying to argue with anyone. I'm trying to focus on one thing here that makes no sense to me, and it's in this recommendation of "Minimum recommended power supply with +12 Volt current rating of 18 Amp," and I'm concerned where they are getting the 18 amp part of it from. It looks to me like the PSU needs to have an available "rail" (if that's the right term) of 12V@18amps, and if you look at my first post the label on the PSU doesn't have this.

And I do appreciate the replies. Thanks.

So here's where you're at. I believe that the 12.8v is designed with enough left over to give you a standard 30W of power at the AGP slot. I say believe because Dell and HP were notorious for only giving half of the power available to a pci-e slot (so you couldn't run high end graphics cards that were designed to run from the slot, the power that was supposed to come from the slot wasn't there, it had to be designed to be powered from a 6pin gpu plug). So I would say go for it. If you're staying in that 20-40W power envelope you should have the oopmh. I believe the 12v rail will pick up the slack. Also, since you're not gaming, stress is minimal. ^_^

 

[thedosbox]

If the power consumption of MX cards is something like 10 watts max, and the power consumption of FX cards is something like 26 watts max., And I have more than 26 watts of power avaiable given all the devices installed on my system, of what significance is the recommended 18 amps?

...
I'm trying to focus on one thing here that makes no sense to me, and it's in this recommendation of "Minimum recommended power supply with +12 Volt current rating of 18 Amp," and I'm concerned where they are getting the 18 amp part of it from.

It's irrelevant, as multiple people have explained. The issue isn't whether your PSU has spare capacity, it's where that capacity lies.

zir_blazer is explaining that the MX cards require more 5V capacity, whereas the FX cards require more 12V capacity.

 

[zir_blazer]

Actually, I didn't mentioned about what the Video Cards uses, just about what the Power Supply can provide. Just that a bit more than a decade ago, the other rails had more importance than 12V until ATX 2.0. Basically, you could have a pre-ATX 2.0 500W Power Supply that would not be good for a modern computer simply because its 12V capacity is low, and you would have a lot of 3.3 and 5V of unused capacity.

As his OEM computer is extremely ancient (Must be from the Pentium 4 Willamate/Northwood or Athlon XP Palomino/Throughbred/Barton era), I won't even recommend spending money on that. Save for a modern budget built.

 

[thedosbox]

Actually, I didn't mentioned about what the Video Cards uses, just about what the Power Supply can provide. Just that a bit more than a decade ago, the other rails had more importance than 12V until ATX 2.0. Basically, you could have a pre-ATX 2.0 500W Power Supply that would not be good for a modern computer simply because its 12V capacity is low, and you would have a lot of 3.3 and 5V of unused capacity.

Fair point, I was being lazy as his fixation on the 18A/12V "requirement" seems to blind him to any explanation of the fine details.

As his OEM computer is extremely ancient (Must be from the Pentium 4 Willamate/Northwood or Athlon XP Palomino/Throughbred/Barton era), I won't even recommend spending money on that. Save for a modern budget built.

This. Though I'm mildly curious as to the objective of trying to upgrade such an old beast.

 

[Petros_k]

Fair point, I was being lazy as his fixation on the 18A/12V "requirement" seems to blind him to any explanation of the fine details.

Not being "blind," just trying to focus on only one aspect of the recommendations to run the card that I'm being told simultaneously are a) grossly exaggerated, and b) is a function of Volts x Amps (ultimately watts) but somehow the power supply is distributed in such a way that the 12V "rail" doesn't have the kind of amps that these two cards may require. The latter is a bit tough on the inexperienced to grasp.

Though I'm mildly curious as to the objective of trying to upgrade such an old beast.

It should be obvious. I've got an old system that has one major flaw that I'm trying to fix: poor ability to play Internet videos or video files stored on the hard drive. An AGP video card of the "low" end that I'm looking at isn't more than $40. That gets me a card that takes stress off the CPU and has onboard RAM, both of which will improve video performance. Plus, I'm trying to simply have dual output to two monitor sources. These modifications will get me a much better system that's not so bad for my purposes (again, I'm not a gamer). The difference in cost between what I want to do and a new system is hundreds of dollars more.



Again, I really appreciate the advice (even if I only understand 3/4 of it). Thank you.

 

[thedosbox]

Not being "blind," just trying to focus on only one aspect of the recommendations to run the card that I'm being told simultaneously are a) grossly exaggerated

The point is it's the wrong thing to focus on as it's a "let's be safe" number chosen by the video card manufacturers. It does not tell you how much power the card itself requires.

and b) is a function of Volts x Amps (ultimately watts)

This is Electronics 101. It is meant to illustrate the relationship between Amps and Watts.

but somehow the power supply is distributed in such a way that the 12V "rail" doesn't have the kind of amps that these two cards may require. The latter is a bit tough on the inexperienced to grasp.

I suggest you read your own link, specifically where they talk about the power characteristics of the AGP slot.

In addition to the sticky threads in this forum, silentpcreview has a nice long explanation of power supply fundamentals:

http://www.silentpcreview.com/article28-page1.html

It should be obvious. I've got an old system that has one major flaw that I'm trying to fix: poor ability to play Internet videos or video files stored on the hard drive.

For those purposes, you might want to consider this:

http://www.newegg.com/Product/Produc...82E16822136997

Costs less than $100, can stream videos from a LAN source (or various internet services), is quieter and consumes much less power than that desktop.