Not enough Amps?

[8bitG33k]

I just recently bought the Antec CP-850 Powersupply based off the excellent reviews I have read. Now, after doing a little research on a new vidcard, I am having second thoughts about this PSU: When I was looking for a new videocard on newegg, I came across the EVGA 560. The specs for this card state that a minimum 12V current rating of 30A is required to operate this vidcard. The CP-850 features "only" 22A on the 12V line.

Bottomline, have I made a mistake buying this PSU? Should I have paid more attention to Amperage on the respective lines, especially on the 12V? Have I have limited my choices as to which vidcard I can buy and will I ever be able to overclock a CPU with this PSU?

 

[serpretetsky]

+12V1@22A, +12V2@22A, +12V3@25A, +12V4@25A,

You have four 12V lines, So unless you're doing something crazier than dual SLI/Crossfire 580's or 6970's and a single processor, you're fine. If you Are doing something crazier, just get back to us with the details.

Also, most reviews point it it being a big unit, hopefully you have enough space for it.

 

[8bitG33k]

+12V1@22A, +12V2@22A, +12V3@25A, +12V4@25A,

You have four 12V lines, So unless you're doing something crazier than dual SLI/Crossfire 580's or 6970's and a single processor, you're fine. If you Are doing something crazier, just get back to us with the details.

Also, most reviews point it it being a big unit, hopefully you have enough space for it.

But it's quad rail, they each have they're own rail...

Yes, I have enough space, after making enough space

 

[Zero82z]

The video card requirements refer to the combined required +12V capacity for the entire system. In other words, EVGA is telling you that your PSU should be able to deliver at least 30A to all of your PC hardware combined, not just the video card itself. A single 22A rail can deliver more than enough power for a 560. Your PSU is absolutely fine.

 

[E4g1e]

The video card requirements refer to the combined required +12V capacity for the entire system. In other words, EVGA is telling you that your PSU should be able to deliver at least 30A to all of your PC hardware combined, not just the video card itself. A single 22A rail can deliver more than enough power for a 560. Your PSU is absolutely fine.

For the record, the combined total +12V capacity of the CP 850 is 64A (768W).

 

[8bitG33k]

For the record, the combined total +12V capacity of the CP 850 is 64A (768W).

Ok, so it doesn't matter if it's quad rail or single rail? This guy here is implying that it does matter.

The way I understand it, is that if they are on a single rail, the total is 64A, just like you say. But if, as in my case, they are on separate rails, the total combined doesn't matter as they have separate rails, 22-24A each rather than ~64 combined...

Sorry, not trying to be a pain, I'm just trying to understand the whole Amp thing.

 

[Zero82z]

Ok, so it doesn't matter if it's quad rail or single rail?

In your case, no.

The way I understand it, is that if they are on a single rail, the total is 64A, just like you say. But if, as in my case, they are on separate rails, the total combined doesn't matter as they have separate rails.

The power is divided between different rails. Assuming the OCP is actually set to 22A on each rail (meaning the PSU will shut off if you go over that amount), that means you won't be able to draw more than 22A from a single one. However, that PSU is designed so that its connectors are balanced across all four rails. You won't end up in a situation where you overload one rail while not using another one.

 

[8bitG33k]

In your case, no.

The power is divided between different rails. Assuming the OCP is actually set to 22A on each rail (meaning the PSU will shut off if you go over that amount), that means you won't be able to draw more than 22A from a single one. However, that PSU is designed so that its connectors are balanced across all four rails. You won't end up in a situation where you overload one rail while not using another one.

THAT'S the explanation I've been looking for! It makes sense.

 

[nikhil pali]

You should be fine. I'm running 580 and 260 in 750 PSU till my new one comes.
You won't face any problem even if you sli 560.

 

[Mthr1]

Ok, so it doesn't matter if it's quad rail or single rail? This guy here is implying that it does matter.

The way I understand it, is that if they are on a single rail, the total is 64A, just like you say. But if, as in my case, they are on separate rails, the total combined doesn't matter as they have separate rails, 22-24A each rather than ~64 combined...

Sorry, not trying to be a pain, I'm just trying to understand the whole Amp thing.

Single vs Multiple rails is an inconclusive argument. So, it really comes down to what you want to believe and what is more important to you.

Most multiple rail PSUs are a result of a single rail that is divided into multiple rails, amperage limited to each. There are a few high power PSUs in the market that are "true" multi-rail design. There are those that say multiple rails produces more cleaner power output than single rail counterparts. This is arguably false. There are those that say a robust single rail offers the best flexibility for a wide spectrum of design blueprints, particularly designs that utilize several high power hardware sources (SLI, Crossfire, big OC'd procs, etc...). Whereas you can find varying levels of validity to each claim, one of the more feasible reasons is multiple rail PSUs are said to be safer in terms of overload and thermal-electric failure that may result in fire. Think of it similar to your household load center. Single rail is like having the whole house electric requirements coming purely off a 100A main lug as opposed to a load panel that has the 100A lug distributed into multiple circuit breakers.

I run all single rail PC Power and Cooling PSUs in all my boxes. Reputable manufacturers need to be ensured when choosing single rail power supplies.

 

[Zero82z]

Reputable manufacturers need to be ensured when choosing single rail power supplies.

You need to ensure you get a PSU made by a reputable manufacturer regardless of whether the PSU is a single or multi-rail unit.

 

[Mthr1]

You need to ensure you get a PSU made by a reputable manufacturer regardless of whether the PSU is a single or multi-rail unit.

Agreed. That goes without saying, of course. Particularly so when considering single railed models.

 

[dewi_imut]

+12V1@22A, +12V2@22A, +12V3@25A, +12V4@25A,

You have four 12V lines, So unless you're doing something crazier than dual SLI/Crossfire 580's or 6970's and a single processor, you're fine. If you Are doing something crazier, just get back to us with the details.

Also, most reviews point it it being a big unit, hopefully you have enough space for it.

....That would be more than enough...the meaning from the card requirement is combined +12v.

And 850w is still enough even to run 4870x2 in crossfire, and I'm sure it still can hold all current single new GPU like GTX580 all right.

 

[8bitG33k]

....That would be more than enough...the meaning from the card requirement is combined +12v.

And 850w is still enough even to run 4870x2 in crossfire, and I'm sure it still can hold all current single new GPU like GTX580 all right.

It's not the Wattage, it's the Amps I'm concerned/ trying to educate myself about. The part I'm trying to grasp is if the CP-850 uses all 4 together then I'm way more than safe.If not then I am underpowered.

 

[HOOfan_1]

It's not the Wattage, it's the Amps I'm concerned/ trying to educate myself about. The part I'm trying to grasp is if the CP-850 uses all 4 together then I'm way more than safe.If not then I am underpowered.

When EVGA is saying you need 30A, they don't mean the graphics card is going to use that much current. They are just assuming a typical computer that a person would install that graphics card into would require that much current. That means, the graphics card, the CPU, the hard drive motors etc. The GTX 560 is probably going to use 13A-16A maximum. It is going to be pulling that current through 3 sources. 2 PCI-E connectors and the PCI-E slot on the motherboard.

OK the CP-850 has a separate rail set up for the CPU, so your graphics card is not drawing current from the same rail as the CPU.

The CP-850 has a rail for the ATX connector the SATA connectors and the various peripheral connectors, so your cards PCI-E slot connector is drawing from the same rail as the hard drives etc....but none of this stuff draws much current and the card won't draw much current from the PCI-E slot either, and you have a full 22A for that.

Then the PCI-E connectors have 2 separate rails for 4 possible connectors that is 50A total for the PCI-E connectors.

Bottom line is you are more than fine.

 

[8bitG33k]

When EVGA is saying you need 30A, they don't mean the graphics card is going to use that much current. They are just assuming a typical computer that a person would install that graphics card into would require that much current. That means, the graphics card, the CPU, the hard drive motors etc. The GTX 560 is probably going to use 13A-16A maximum. It is going to be pulling that current through 3 sources. 2 PCI-E connectors and the PCI-E slot on the motherboard.

OK the CP-850 has a separate rail set up for the CPU, so your graphics card is not drawing current from the same rail as the CPU.

The CP-850 has a rail for the ATX connector the SATA connectors and the various peripheral connectors, so your cards PCI-E slot connector is drawing from the same rail as the hard drives etc....but none of this stuff draws much current and the card won't draw much current from the PCI-E slot either, and you have a full 22A for that.

Then the PCI-E connectors have 2 separate rails for 4 possible connectors that is 50A total for the PCI-E connectors.

Bottom line is you are more than fine.

Thank You for that explanation, it's making more and more sense now. Also, I've been reading up on Amps and Volts and Watts and what the definitions are and how they "interact".

 

[serpretetsky]

Thank You for that explanation, it's making more and more sense now. Also, I've been reading up on Amps and Volts and Watts and what the definitions are and how they "interact".

usually the easiest way to imagine volts and amps is thinking of water pipes. Voltage is the water pressure, and amps is the water current.

 

[Zero82z]

usually the easiest way to imagine volts and amps is thinking of water pipes. Voltage is the water pressure, and amps is the water current.

That analogy is common, but it's not very accurate.

 

[Topweasel]

Those pieces of information are included because of issues people can run into with poor PSU's and older units from when the Watt war was in its infancy.

For example I have an old Thermaltake 650Watt unit when 800 watt units were just hitting the market and were $300 or higher. Cost me $150 and probably wasn't a great purchase even then but it was one of the few that came pre-sleeved at the time.

As a 650 watt PSU, it is a single rail unit with 28 amps available on the 12V. Where it was also really generous to the 5v and 3.3v rails to make up the difference to hit the 650w they were selling it as.

A 650watt now should work easily with a Quad or 6 core CPU and a high end video card easily. But in my system it was always an inch from death and eventually failed out, all the while being horribly inefficient.

 

[EmualDave]

a frind of mine have a the same PSU as yours and runs GTX 480 OC without problem.

running GTX 560 TI will be a pice of cake for your PSU

Enjoy the ride

 

[fullback100]

This is my personal experience. I had SLI-Certified Antec Neo HE 500 with 3 multi rails. When I plugged a new GTX 460, my mobo and video card went South. Of course, all PCI-E connectors are done properly. After the incident, my PSU is producing a high pitched noise. I don't know what went wrong but it gave me a feeling that I probably buy single-railed PSUs in the future.

 

[Zero82z]

This is my personal experience. I had SLI-Certified Antec Neo HE 500 with 3 multi rails. When I plugged a new GTX 460, my mobo and video card went South. Of course, all PCI-E connectors are done properly. After the incident, my PSU is producing a high pitched noise. I don't know what went wrong but it gave me a feeling that I probably buy single-railed PSUs in the future.

The NeoHE 500W is a single-rail PSU.

 

[8bitG33k]

To conclude: I have 4 PCI-E lines on two separate rails, which gives me 50 Amps per rail. Since the 560's requirements are 30 Amps, I have more than enough as most PSU's run their 12V lines off a single rail. Even if the 4 PCI-E lines ran on a single rail, I'd (probably) still have enough since nVidia is making a very conservative assumption that most use a single rail 12V for all components.

 

[BinarySynapse]

To conclude: I have 4 PCI-E lines on two separate rails, which gives me 50 Amps per rail.

No you have 22 amps per rail regardless of now many PCIe lines there are. Using a specific combination would allow you to use two rails to supply up to 44 amps to a set of cards. But that would require a much more power powerful setup.(e.g. three GTX580's). But in your case, it would be quite pointless to worry about how your splitting the lines.

Since the 560's requirements are 30 Amps, I have more than enough as most PSU's run their 12V lines off a single rail. Even if the 4 PCI-E lines ran on a single rail, I'd (probably) still have enough since nVidia is making a very conservative assumption that most use a single rail 12V for all components.

Again, Nvidia isn't saying the 560 needs 30A, They're saying that an entire system with a 560 in it could potentially draw up to 30A and you need to make sure your power supply is capable of supplying enough to power to your video card without sacrificing what it can supply to the rest of the system. Yours can do that with great ease.

The 560 only uses 170w of power. That's just under 15 amps at 12v. Of that 170w, 75 is provided by the PCIe slot. So That's 6a off your total, leaving 9 amps being drawn from the two PCIe power connectors (which the PCIe spec limits to 6A for each 6 pin).

 

[8bitG33k]

Again, Nvidia isn't saying the 560 needs 30A, They're saying that an entire system with a 560 in it could potentially draw up to 30A and you need to make sure your power supply is capable of supplying enough to power to your video card without sacrificing what it can supply to the rest of the system.

I may have not expressed it adequately enough but that's what I was trying to say.

In a nutshell, I have 84A.

 

[MrWizard6600]

I may have not expressed it adequately enough but that's what I was trying to say.

In a nutshell, I have 84A.

You do.

I've never heard the explanation Mthr1 gave.

The primary reason for splitting rails is a very simple one: safety. If you have a single 12V 80A line, if something gets shorted that kind of power can turn aluminum into molten metal no problem. By dividing up the lines they can apply some degree of sane Over Current Protection (OCP) thus limiting the possibility of something shorting and causing a fire.

I don't know what systems unified rail PSU's use, but I suspect they fuse each pin-out individually to ensure that no one wire ever exceeds capacity, 240W as per IEEE.

As for the split rail PSU's, they've cleverly laid things out so as to make sure its very difficult to actually try to pull more than the rated capacity from any 1 rail, but if you do have problems, come back to these boards and we'll be more than happy to look up some data sheets to find out exactly what you should connect where.

I know most people on these boards wont believe it, because the specs you read in everyday PSU's tell us not to, but a single ampere (1A) is a huge amount of electricity. Significantly less is required to kill somebody, significantly less is required to get serious work done, and when you get into these high current ratings electronics become intrinsically dangerous.

 

[Tsumi]

usually the easiest way to imagine volts and amps is thinking of water pipes. Voltage is the water pressure, and amps is the water current.

Not quite accurate, I'll just give another one using water pipes.

Voltage is the water pipe cross-sectional area (how wide it is), and amperage is the speed of the water through the pipe. Wattage is the volume, or amount, of water that flows through the pipe. To get the volume of water, you simply multiply the area by the speed. Similarly, to get the wattage, you multiply the amperage times the voltage. Increased voltage at the same amperage yields increased wattage, as does increased amperage at the same voltage.

Either way, the point is, that power supply would be enough for SLI GTX 580. You're fine with a single 560.

As for the multi-rail vs single-rail argument, there hardly is anything in there, it's more of just marketing hype companies use. Some argue single rails offer better stability, others argue multi-rails offer better protection. Really, the best way to get better stability/protection is to buy a good quality power supply, period. There is negligible difference between a multi-rail and a single-rail power supply of the same quality.

My personal preference would be a single-rail design, so that you don't need to worry about overloading one rail (although the OCP limits on a rail is probably much higher than the rated limit). Many of the top designs use single-rail designs, like the Corsair AX series and Seasonic X series.

Edit:

Also, most, if not all, designs under 1000 watt really use only one 12v power source (true rail). The source is then split into 1, 2, 3, or 4 lines, depending on however many rails the power supply is said to have. Whether or not each of these individual lines have OCP depends on the quality of the power supply and the design. Usually, it's cheaper to have multiple lines in larger power supplies because they can use smaller wires. Arguably, this is worse than single or dual rail designs because the wires have a higher chance of overheating/melting. Usually, the main OCP will protect the power supply, and often it is better that way. If you somehow load everything into one rail, you'll get random shutdowns cause you're overloading one rail, even though you're not approaching the power supply's limits. With a single rail, you wouldn't need to worry about this. But as I said above, the most important thing is PSU quality, not the amount of rails. Rails can actually be ignored when making buying decisions.

 

[HOOfan_1]

No you have 22 amps per rail regardless of now many PCIe lines there are.

Actually Antec labels the circuits for the PCI-E cables as 25A

http://www.jonnyguru.com/modules.php?name=NDReviews&op=Story&reid=142

Their own website shows the OCP set point is 37A though

http://www.antec.com/Believe_it/product.php?id=NzIw

 

[Zero82z]

Usually, it's cheaper to have multiple lines in larger power supplies because they can use smaller wires.

Huh? The size of the wires has nothing to do with the number of rails. It's generally more expensive to build a multi-rail PSU since they need to add circuitry for the OCP. Most single-rail PSUs don't even have OCP altogether.

 

[BinarySynapse]

Actually Antec labels the circuits for the PCI-E cables as 25A

http://www.jonnyguru.com/modules.php?name=NDReviews&op=Story&reid=142

Their own website shows the OCP set point is 37A though

http://www.antec.com/Believe_it/product.php?id=NzIw

I hadn'tt looked at the specs, and was going with what he stated in his original post. Whatever they are, my point stands.

 

[Madcap]

I agree with what's been said, you should be fine.

 

[8bitG33k]

I hadn'tt looked at the specs, and was going with what he stated in his original post. Whatever they are, my point stands.

Yep, those are the specs I posted. The way Antec states it, it reads that there are 2x22A & 2x25A 12V rails, and each has an OCP of 37A. I assume they mean you can't pull more than 37A from any specific combination.

The PCI-E lines have 2x25A each, and there are four of them, giving me 50A per card. As you say, more than enough, especially considering these are dedicated PCI-E lines.

On a side note, it is actually 94A total, as 2x22+2x25=94, not 84.

 

[BinarySynapse]

Yep, those are the specs I posted. The way Antec states it, it reads that there are 2x22A & 2x25A 12V rails, and each has an OCP of 37A. I assume they mean you can't pull more than 37A from any specific combination.

The PCI-E lines have 2x25A each, and there are four of them, giving me 50A per card. As you say, more than enough, especially considering these are dedicated PCI-E lines.

50A total. If you have two cards using all four PCIe connections, the most you can get to each card is going to be 25A through those connectors (the PCIe design spec imposes more limits that I'm going to ignore for now). If you have 4 cards, each one will only get 12.5a (ignoring the PCIe imposed design limits again).

On a side note, it is actually 94A total, as 2x22+2x25=94, not 84.

It's actually 64A for your power supply. If you look at the label, the combined 12v power is limited to 768watts.

 

[8bitG33k]

50A total. If you have two cards using all four PCIe connections, the most you can get to each card is going to be 25A through those connectors (the PCIe design spec imposes more limits that I'm going to ignore for now). If you have 4 cards, each one will only get 12.5a (ignoring the PCIe imposed design limits again).

Even though they are on two separate rails? 2x25 on one rail and another 2x25 on another rail, all dedicated PCI-E...

Just to be sure, my original question has been answered, at this point I'm just trying to learn more.

 

[BinarySynapse]

Even though they are on two separate rails? 2x25 on one rail and another 2x25 on another rail, all dedicated PCI-E...

Just to be sure, my original question has been answered, at this point I'm just trying to learn more.

You seem to be thinking that a 25a rail supplies 25a to each connector. The most that a rail can supply (ignoring the actual OCP limit for now) is 25a. It has to be split up for each device connected to that rail. Two connectors will get a total of 25a, so 12.5a each (or 13/12 14/11, etc). So with two 25a rails gives you 50a to split up.

Think of it like a water line that can supply 25 gallons per minute. If you put a house at the end of the water line, it can use the full 25gpm supplied to it. However, if you add another house to the end, the most each house will get (when using the line at the same time) is 12.5gpm. The more houses you add, the less the line can supply to each house at once.

 

[Tsumi]

Huh? The size of the wires has nothing to do with the number of rails. It's generally more expensive to build a multi-rail PSU since they need to add circuitry for the OCP. Most single-rail PSUs don't even have OCP altogether.

Then what about top-end Corsair and Seasonic power supplies, which are almost exclusively single-rail designs? Are you telling me that those do not have OCP? Get your facts straight.

The size of wires have something to do with it. The larger the wire, the more current it can handle before overheating and melting, this all has to do with the resistance of a wire. With a single rail, you need one large wire to deliver power from the 12V source to the connector board, which distributes power to your components. With a multi-rail, you have smaller wires which are cheaper delivering power to separate connector boards. And it is required to have OCP on each of these wires because if you overload them too much, they will overheat and melt.

 

[BinarySynapse]

Then what about top-end Corsair and Seasonic power supplies, which are almost exclusively single-rail designs? Are you telling me that those do not have OCP? Get your facts straight.

The size of wires have something to do with it. The larger the wire, the more current it can handle before overheating and melting, this all has to do with the resistance of a wire. With a single rail, you need one large wire to deliver power from the 12V source to the connector board, which distributes power to your components. With a multi-rail, you have smaller wires which are cheaper delivering power to separate connector boards. And it is required to have OCP on each of these wires because if you overload them too much, they will overheat and melt.

He said most single rail supplies and nothing about them being top end.. Corsair and Seasonic make nowhere near most of the single rail supplies. His point was that the cost of implementing multiple rails overrun the cost of a larger gauge wire, even more so when you consider that most (read cheap/mediocre) single rail supplies don't even have OCP.

 

[Zero82z]

Then what about top-end Corsair and Seasonic power supplies, which are almost exclusively single-rail designs? Are you telling me that those do not have OCP? Get your facts straight.

The size of wires have something to do with it. The larger the wire, the more current it can handle before overheating and melting, this all has to do with the resistance of a wire. With a single rail, you need one large wire to deliver power from the 12V source to the connector board, which distributes power to your components. With a multi-rail, you have smaller wires which are cheaper delivering power to separate connector boards. And it is required to have OCP on each of these wires because if you overload them too much, they will overheat and melt.

They probably have OPP, not OCP. OCP isn't needed when you have a PSU that is rated to deliver 99% of its total power rating through a single +12V rail, since once you exceed that limit, the OPP is going to trigger anyway. OCP would be redundant.

Yes, a single large wire can be used to transport all the power from a single rail. However, in practice this is usually not done. The Seasonic X-750, for example, has a single 62A +12V rail, but it uses several smaller wires in parallel to connect the modular PCB to the secondary side, as you can see in this picture. This especially goes for non-modular single-rail PSUs, since multiple wires are required anyway in order to accommodate the assortment of connectors provided by the unit. In those situations, all of the wires are connected directly to the main PCB.

Multi-rail PSUs do not have OCP on each wire, they have OCP on each rail. Even with multi-rail designs, there are often multiple wires connected to each rail, but the actual OCP is implemented on the PCB, not on the wires. And like I said earlier, implementing separate OCP circuits for each rail is technically more expensive than a single OCP circuit or none at all, like single-rail designs.