[SOLVED] How a Graphics Card draws power?

[RMS_01]

Hi everyone, I am rather new to the concept of building your own PC. I am looking at upgrade options for a low budget SFF (HP DC7900). However, I do not have a very clear understanding of how a Graphics Card draws power.

An example is:

A PCIe x16 port on my Motherboard supports up to 25W power.​

A Graphics Card that I have done basic research on (AMD Radeon HD 7770) requires 80W power but has a 6-pin connector​

A PSU that I could potentially buy has about 500W total power (that's much more than what I currently have.)​

​

What I'm trying to understand is, if the PSU is going to provide all the power for the Card (or is it?), do I need to worry about the 25W Limit on the PCIe Slot?

Thanks in Advance

 

[Darkbreeze]

PCIe x16 slot power has to be able to support up to 75w by specification.

A 6 pin connector has to be able to support 75w by specification.

An 8 pin connector has to be able to support 150w by specification.

So a graphics card with two 8 pin connectors could theoretically have the ability to draw up to 375w, but would typically draw considerably less than that, but could also technically spike to slightly more than that.

Buying an HD 7770, NOW, 7 years after it was manufactured, would be a really poor idea. Any HD 7770 has likely already seen the majority of it's useful life expectancy pass by. Unless you could get the card for less than fifty bucks, I'd pass.

What the listed capacity of ANY power supply is, is not nearly as important as what the MODEL of the PSU is, so that it's quality can be gauged. There are FAR more power supplies out there that claim to be 500w units that can't reliably sustain 350w, then there are ones that either can sustain their listed capacity or even exceed it. Which means, there are a whole LOT of crappy power supplies out there and just because it SAYS 500w, does not by any stretch of the imagination mean that it actually can. Even a fair number of well known brands have significant numbers of models that are very poor quality.

So, knowing what MODEL that unit is you are looking at would be a very good idea, and would allow us to help you to decide whether it's a complete waste of your money or a pretty safe bet, one way or the other.

What country are you in?

How much are you able to spend on a graphics card and power supply?

What EXACTLY is this system going to be primarily used FOR?


For future reference, I prefer to use THIS list of recommendations when it comes to how much capacity a given graphics card should be supported by when choosing a PSU. Yes, in some cases the numbers are slightly more than what is strictly necessary, but that is by design, to offer some measure of headroom for the sake of safety and the health of you PSU, graphics card and motherboard. You won't make a mistake if you use this for assessing how much capacity you should be looking for. But keep in mind, that is IF you are also going after a quality power supply. Not a mediocre or cheap unit.

http://www.realhardtechx.com/index_archivos/Page362.htm

 

[RMS_01]

Hey, thanks a lot for your clarification. I now can look at more options for my setup. Perhaps a better Motherboard that supports a higher PCIe wattage (among other things) is on the cards.

I might add that the PSU & other stuff I listed were theoretical options. I still am not fully committed to purchasing anything right now.

I live in New Zealand, and PC components are definitely not affordable when purchased brand new. That's why I'm relying on second hand parts to complete my setup.

I am now starting to believe that this SFF will probably be used for general usage, possibly (very) light gaming.

Once again, thanks for your input, and now I'll be looking for more options

Thanks

 

[Darkbreeze]

Anytime man. I definitely understand the high cost of hardware is NZ, AU and CA. I suppose the fact that mostly none of it is made there has something to do with it, and yet, most hardware is made in China and it's probably more costly to ship to the US than to Aussies, but maybe it's due to high import duties or something. Regardless, I realize that, and understand it is an important factor.

 

[RMS_01]

Ok then, to your knowledge, what do you think I could do? I've got Max 8gb RAM in it, I might be getting a Core 2 Quad Q9550. I've still got only 240W of PSU power. What on Earth could I potentially buy in regards to a Graphics Card? I'm really struggling to find one that is the best balance of age / Wattage / Memory. Any ideas?

 

[Darkbreeze]

I'd try to see if you can find a GTX 950, 1050 or 1650 or even a GTX 750 which given the capabilities of your hardware even if you upgrade that platform, might be the more appropriate fit and none of which should require more than just slot power.

Or, on the AMD side of things, I'd look at finding an R7 250 (Pretty weak), HD 7750 or R7 350, also none of which require supplemental power and need only the 75w from the slot that should be capable of being supplied by most OEM power supplies that come preinstalled in units like those from Dell and HP.

 

[RMS_01]

Hi again, I'm looking at some graphics cards, and I have seen some that are plausible enough to work modestly in my setup. However, they are always a little higher than my rated maximum PCIe Wattage (BTW I found out I have 35W Max from PCIe x16). Should I be looking elsewhere if some graphics cards are rated at 37-40W? Will they fail without the extra 3-5 Watts?

 

[Darkbreeze]

ALL x16 PCIe slots MUST be capable of supporting up to 75w. That is not optional. They MUST be able to do that or they cannot carry the PCIe certification and call the slot a PCIe x16 slot. It HAS to be able to support up to 75w slot power. ALL motherboards.

ANY graphics card that does not specifically require a 6 or 8 pin supplemental power connector will work with that motherboard without a higher capacity power supply as long as the power supply that it has is capable of supporting the system it came with or was installed in.

Basically, ANY graphics card that does not need an additional 6 or 8 pin power connector to operate will work fine, as long as it is not too new to work with the legacy BIOS that your motherboard has. Some newer graphics card architectures will not work with older legacy BIOS. That is why I suggested older card models that I know are compatible with legacy BIOS motherboards.

To be honest, I would not try to use any graphics card newer than the Nvidia 900 series or the AMD R9 200 series models. Possibly even older if you can still locate them new or find a trustworthy used purchase which can be fairly risky.

 

[RMS_01]

ALL x16 PCIe slots MUST be capable of supporting up to 75w. That is not optional. They MUST be able to do that or they cannot carry the PCIe certification and call the slot a PCIe x16 slot. It HAS to be able to support up to 75w slot power. ALL motherboards.

Well, OK then. Ahhhh, I am genuinely surprised by that. And yes, as I have just read on other forums, that indeed PCIe's have no reason to be limited.

All sizes of ×16 cards are initially 25 W; like ×1 cards, half-height cards are limited to this number while full-height cards may increase their power after configuration. They can use up to 75 W (3.3 V×3 A + 12 V×5.5 A), though the specification demands that the higher-power configuration be used for graphics cards only, while cards of other purposes are to remain at 25 W.

This excerpt came from a Dell SFF Forum, and he asked why his PCIe was limited. Would this answer sum it all up?

 

[Darkbreeze]

Yes. Cards themselves might be limited to a specific limit based on the type of card they are, but the PCIe x16 slot ITSELF, has to be capable of supporting the full 75w. That means you can use any 75w or lower card in any x16 PCIe 2.0 or 3.0 slot as long as it's a card that doesn't also require a six or eight pin connector. Then, you must also have a PSU with the required connector in order to use such a card.

 

[RMS_01]

Thanks a lot for all this @Darkbreeze. You've really cleared up my confusions, and now I realise my options are now merely restricted by my budget. Geez, if I knew about this a week earlier, I probably would've scored some decent hardware. Oh well, they always pop up every now and then.

Thanks
Roidan

 

[Darkbreeze]

For sure. One further thing you want to be aware of is that since you DO have somewhat older hardware IIRC, then before purchasing any specific graphics card you might want to check around and do a search to verify that THAT specific card will work in your motherboard. Not because of anything to do with power, just to make sure that it's a card that works on your specific board since it is a legacy BIOS, and an older one if you're running an older core2 type platform.