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Graphics card with external power supply

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April 23, 2010 2:43:16 PM

I'm thinking about adding a new graphics card to my old Dell Optiplex 755. As it's a small case, I'm looking at 9800GT low profile or GTS 250 low profile. Here comes the *potential* problem.

I opened the case and found 1 PCI-e slot with marking (16,1) 25W which I think it's PCI-e x16, but the 25W really scared me. Does that mean it can only support 25W card? That means I cannot install that card though my PSU is rated 280W.

So it looks like adding a external power supply is a must. My question is: Will the card smart enough to pull the power from the external/secondary 6-PIN connector instead of the poor 25W slot?

Could someone please give me some advice. Thanks.
April 23, 2010 6:33:14 PM

you've got it all wrong...
a 9800 eco/green version or a ati 4670 will run on ur pc... they don't require separate power from the psu and will draw the same via the pci-e slot..
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April 23, 2010 6:55:30 PM

Wow, that's quick reply. Thanks.

I do understand that a card like 9800 green or 4670 would run. But the performance, h, let's say, is not so good. What I'm looking at is getting the max performance even if I have to invest more. Bottom line is to keep it in this form factor. I have found a reasonable 5.25 inch GPU power supply with 300W available at local market. But I'm really concerned that even if I plug this to the 6-PIN connector, those stronger cards would still cry for power from the PCI-e slot. In this case, it's a "no way".

Are you really saying that my thought is a "no way"? That's sad..... I'm so confused of this 25W slot...

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April 23, 2010 9:39:43 PM

I've never heard of a PCI-E slot only providing 25Watts of power. If it's a PCI-Express x16, it provides 75Watts.

For a small performance card, an HD5670 will be perfect. Consumes ~25watts of power on load, and is better than the 9600GT.
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April 23, 2010 10:41:53 PM

Me either, honestly. Until I see this when I opened my case.....
Call me greedy cause I'm really into these more modern cards. So the question's still open. Will external power supply override the stupid 25W limitation?
Thanks for the reply, though.

Oh, here's the suspicious slot
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April 24, 2010 2:57:53 AM

yes it will use external power supply no problem the pcie slot is the same on all mother boards
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April 24, 2010 9:17:19 PM

Thanks, Marco324.
But if all mother boards come the same, why haven't I seen this 25W marking on the others? Doesn't it mean power limit? I don't really think it's a trade mark or something...

Any more input? Anyone? Keep it coming, please.
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October 13, 2011 6:33:18 AM

ericcire said:
Thanks, Marco324.
But if all mother boards come the same, why haven't I seen this 25W marking on the others? Doesn't it mean power limit? I don't really think it's a trade mark or something...

Any more input? Anyone? Keep it coming, please.


Found this old thread while looking into using a PCIe graphics card in my Dell server so i thought of resurrecting it and pass on what i found so others may learn :p 

Not all x16 slots are the same :p 

Like the OP, my problem was that the PCIe slot in my server was only stated to support 25W card. This is compliant with PCIe specs but the confusing part was that the PCIe specs differentiate between 'normal' PCIe x16 slots and 'graphics' PCIe x16 slots. Both slot types support maximum 10W start up power before the card negotiates its power draw but only the later 'graphics' PCIe slot is certified to draw up to 75W.

The difficulty is not knowing what physical differences exist between the power feeds to a 'normal' x16 slot as compared to a 'graphics' x16 slot (whether the power traces and slot pins are thicker in a x16 graphics slot as compared to a normal x16 slot). Dell wont tell :(  The other difficulty is not knowing how the PCIe power up routine works and actually negotiates the PCIe cards maximum power draw, or whether a graphics card PEG connector (which can draw up to 75W for 6pin PEG or 100W for 8 pin PEG) can take up any deficiency in PCIe power draw when a graphics card is used in a 'normal' x16 slot or an 'normal x8 slot (obviously as long as the card is still within its limits, total PCIe+PEG power draw & individual PCIe/PEG draws). I have not resolved this yet.

I got around my problem by using a low power 'XFX 7600 GS' graphics card but the kicker was that my server didn't have a x16 slot, so i cut away pin traces 50, 51 & 52 (from memory) so it would fit into the x8 slot and now works a treat :D 

I am still not satisfied and still trying to resolve if there is any mechanical issues w.r.t. 25W/75W and whether a graphics card can intelligently apportion power draw between PCIe and PEG. Once i answer that, i can purchase a more powerful DX11 card and happily put it into my beast.

So if anyone @ tomshardware actually knows the PCIe specs w.r.t. negotiation of maximum power draw and PCIe/PEG power apportioning mechanisms, do share :p 
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October 16, 2011 6:56:34 AM

I'm surprised to see a reply after the thread has been inactive for so long.

Actually after I got no clear answer from the internet. I said "what the hell" and went ahead to buy a Sparkle GTS 250 low profile card which claimed to a 100 Watt (not very sure about the number, but definitely over 25W) power consumption.

I installed it on this very slot and use an IDE(molex?) power to 6 pin converter to pull "some" extra power from the same Dell 250W power supply and it's been working well for 1 year.

I looks like Dell PC is quite capable of working over spec.

Hope this helps.
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a c 271 U Graphics card
a b ) Power supply
February 10, 2012 6:00:52 PM

This topic has been closed by Mousemonkey
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