GPU vs Power Supply

Praxis · Post by **Praxis** » 2008-02-06 05:42pm

Working on a problem for a friend here...

He's got a HP a6120n desktop PC ( motherboard specs).

He's looking to buy a Geforce 8800GT (this one specifically: http://shop4.outpost.com/product/5434319 ).

It looks like it requires either two 4-pin Molex or one 6-pin PCIe power adapter.

I'm not sure how to tell whether his machine meets that requirement. Can anyone here help?

EDIT: Whoops, it's the power supply I need to ask about.

Uraniun235 · Post by **Uraniun235** » 2008-02-06 05:54pm

I'm not sure what the power connector requirements have to do with the motherboard. The card should work with the motherboard itself. It sounds like the question you're asking is whether or not the power supply will support the video card... which the HP website doesn't seem to have any information on.

InnocentBystander · Post by **InnocentBystander** » 2008-02-06 05:57pm

As long as the motherboard supports PCIe x16 (it does) its fine. You will have to look at the power supply to see if it has the spare cable. The GPU will most likely come with a converter if all he has is a spare 4 pin.

Post by **Sea Skimmer** » 2008-02-06 07:35pm

So far as I can tell from customer reviews, nowhere do sellers list the actual power supply specs of this thing, the a6120n has a 250 watt PSU. No way in hell will that support an 8800GT, that card officially needs a 400 watt unit able to output 22 amps on the 12v rail as a minimal, but in reality he should get a higher power unit if he upgrades. It will be much more stable, 400 watts would be really marginal, and since the transformers aren’t being highly taxed they’ll run more efficiently and cooler, saving money on electricity and extending the life of the entire computer.

I myself have a 950 watt power supply, which could almost power my Intel quad core and 8800GTS setup twice over, the result being that even when I’m playing Call of Duty 4 or Silent Hunter 4, the air coming out of the PSU is still only barely above room temperature. Not saying you should go for that insanely of an over capacity PSU (I got a combo deal on Newegg that let me get the 950 watt unit for only 100 bucks, same price as the 600 watt I actually needed) but its an example of what that can do for you.

With only 250 watts, a 7600 GT card is more in line with what he can power, and even that might be too much, I'm not really sure.

lukexcom · Post by **lukexcom** » 2008-02-06 07:58pm

I would just like to add this resource, Extreme Power Supply Calculator.

It will tell you how many watts you need based on the components you tell it and how much capacitor degradation you wish to factor in. That's the free version.

The pay version will also give you requirements such as amps per 12v, 3v, 5v rails required, the ability to factor in multiple graphics cards (tri-SLI or quad-SLI/crossfire), and a UPS rating if you are thinking of getting one.

All in all, I found it very useful when building my own server box and my gaming box.

Uraniun235 · Post by **Uraniun235** » 2008-02-06 08:00pm

400 watts isn't really that marginal; there's been a vicious inflation of the perceived power needs of computer components. The 8800GT, if I remember right, will draw a maximum of ~110W at full load. The E4400 CPU on that computer should draw less than 100W. I doubt the other components would add up to more than 100W, if that.

I can't wait until people start insisting that 1KW power supplies are "vital".

Ariphaos · Post by **Ariphaos** » 2008-02-07 01:16am

InnocentBystander wrote:As long as the motherboard supports PCIe x16 (it does) its fine. You will have to look at the power supply to see if it has the spare cable. The GPU will most likely come with a converter if all he has is a spare 4 pin.

The converter requires two 4 pins, IIRC.

Post by **Sea Skimmer** » 2008-02-07 01:29am

Uraniun235 wrote:400 watts isn't really that marginal; there's been a vicious inflation of the perceived power needs of computer components. The 8800GT, if I remember right, will draw a maximum of ~110W at full load. The E4400 CPU on that computer should draw less than 100W. I doubt the other components would add up to more than 100W, if that.

You can’t get anything like the maximum rated wattage on any one rail. If you don’t have a good 400 watt power supply, and in my personal experience Dell will give you the absolute minimal for the system they sell you, then you could be drawing too much off the 12v rail.

I can't wait until people start insisting that 1KW power supplies are "vital".

As I pointed out a 950 watts is twice what I’d actually need even with running at high efficiency in mind for cooling

Uraniun235 · Post by **Uraniun235** » 2008-02-07 02:13am

I wouldn't be comfortable with saddling a 250W supply with an 8800GT, sure. But we're talking about an upgrade part he'd be purchasing so I'm not sure where Dell fits into the discussion. I realize that you're not going to be able pull 400W off 12V from a 400W PSU, but we're not talking about pulling that much either; and besides, a quality 400W PSU should be quite capable of pushing over 20 amps of 12V juice.

I should have been more careful with my wording, I didn't mean that you were claiming that a 1KW was vital, but certainly there are people out there now who will recommend a 600W (or more!) PSU at the drop of a hat.

Xon · Post by **Xon** » 2008-02-07 04:18am

Uraniun235 wrote:I can't wait until people start insisting that 1KW power supplies are "vital".

My fileserver runs at +250-300watts on startup due to running 11 disks (5x1tb,4x750gb,2x300gb) and a high end RAID card.

When you consider the total wattage of the 12volt rails, this 500watt PSU only supplies ~400Watts. The only reason I got a 500Watt PSU is I needed the physical connectors (spread over 3 12 volt rails) and I needed the high efficiency (aka lower heat output) that running an unstressed PSU provides.

Most cheap PSU have a high overall wattage but lack on the critical 12volt rail.

Uraniun235 · Post by **Uraniun235** » 2008-02-07 10:35am

Well, yeah, crappy power supplies are crappy. This is something I have railed about pretty often here, I think.

Efficiency is not greatest when placing the least load on a power supply; there's a certain point below which efficiency actually tends to decrease, although your system is clearly an unusual case for most people because you've got such a huge initial draw at startup. Although to be fair this is what staggered spinup is meant for.

Arthur_Tuxedo · Post by **Arthur_Tuxedo** » 2008-02-07 12:39pm

I was just going to point that out before U235 beat me to the punch, but I'll second it in case anyone missed it. An 800 W PSU running at 37.5% of capacity will not necessarily be running cooler and more efficient than a 400 W PSU running at 75%. In fact it may very well run hotter and less efficient with such a small load.

Xon · Post by **Xon** » 2008-02-07 05:30pm

Uraniun235 wrote:Although to be fair this is what staggered spinup is meant for.

Staggered spinup requires the raid controller to control the power being delivered (need a backplane or some wierd setup with the PSU which isnt common) or it to support PM2 (which it doesn, stupid thing!)