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How many watts on your pci-e x16 (gen 2)

This is a discussion on How many watts on your pci-e x16 (gen 2) within the RAM and Power Supply Support forums, part of the Tech Support Forum category. Ok, fairly straight forward question. I want to get a HD 7770 but my Powersupply is abit etchy, so I


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Old 11-12-2012, 09:40 AM   #1
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Mistake

Ok, fairly straight forward question.

I want to get a HD 7770 but my Powersupply is abit etchy, so I would like to know EXACTLY how much wattage is coming from my PCI-e port so I can calcutate how many watts I'll need to deliver from the molex.

If its balanced in a ratio between the 6 pin and pci-e can some one tell me cause after a week of reasearch the answers I get are still rather sketchy and to diverse.

Please don't tell me to get a new powersupply, I plan to in January but for now my budget to tight and I want to see if I should keep using my 9400gt till then or if its safe to use the new card with my old power supply.

Some Extra details

450W Powersupply (Generic) Model Number LPG9-25 (Can't find a brand name)

12v rated at 13A and 14A on 2 Rails
12v Max Wattage 260w

Thank You in Advance

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Old 11-12-2012, 10:10 AM   #2
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AMD says 500W minimum for a 7770 GPU. I would want/use nothing less than a good quality 650W.
Regardless, your PSU is not sufficient in power or quality and would need replaced before installing a 7770.

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Old 11-12-2012, 10:28 AM   #3
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The 7770 requires 23 amps of continuous current @ 12 V. Look at the label on the side of your PSU and you will almost certainly see that it is not capable of providing that, not to mention the additional 12 V current to ensure that the other 12 V needs of the system (CPU, fans, hard drives, etc.) are met.

In a nutshell, no you can't run a Radeon HD 7770 from a cheap 450 W PSU. Wait until you can purchase a good quality 650 W unit.

Something like this.
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Old 11-12-2012, 11:00 AM   #4
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Thank you for the reply, but thats whats confusing me.

The 7770 is labelled as a 80W max TDP card then why does it need 23A? P(watts)=V(12v).I(23A) so from that stand point it would use 273W of power?

But thats only half the question, I also want to know is there a set ratio between the 6 pin and PCI-e for power distribution or does it get 75W max from PCI-e and then start pulling from the 6 pin?
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Old 11-12-2012, 11:42 AM   #5
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The card(varies slightly with brand and model) uses 80w the PICIe spec is 75w max from the slot, the card is backwards compatible to the 1.0 spec so it has the 6 pin PCIe power connector to cover the additional 5w design wattage. There is one on the market with no additional power connector and is only compatible with the PCIe 2.1 and greater spec that allows 150w from the slot.

There is no set ratio between the two draw points they will be shared equally since the 12v on the card is a common buss.

It's really a pretty efficient card and runs well on a 520w PSU on normal systems.
What are the rest of your specs?
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Old 11-12-2012, 11:51 AM   #6
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The card is stated to have a typical power consumption of 80W; however, "typical" means things like sending an e-mail, typing a term paper or watching a YouTube video. Gaming power draws are not "typical."

A component will pull power from all available sources to the extent that those sources are capable of supplying it before the overcurrent protection limits them. The problem with running a power-hungry modern video card on a cheap, usually multi-rail, PSU is that, unless you know exactly where to pull 12V power off to feed the card, it will pull more than a single rail is capable of supplying and, in a best-case scenario, cause the protection circuitry to kick in an shut down your computer (in a worst-case scenario you will short out your cheap PSU and potentially damage any or all other components of the system).

Note too that modern quality PSUs will supply nearly all of their power at 12V, whereas cheap OEM PSUs will usually supply large amounts of power on the 5V, 3.3V and other rails that are little-used in modern computers.

Look at the label on the side or your PSU. How many Amps are supplied at 12V?
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Old 11-12-2012, 12:02 PM   #7
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Overall system usage> Gigabyte Radeon HD 7770 OC Video Card Review - Power Consumption - Legit Reviews
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Old 11-12-2012, 11:02 PM   #8
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Those numbers are surprizing, full system load of 230w +- on a high end sytem like that, then why do you need 500W PSU for?

So if Wattage is split evenly between the PCi-e port and 6 pin then I can be expecting around 40W pull on the molex mean around 3.3A, add that to the other stuff connected to them (2 hdd, 1 dvd drive) I should be expecting around a max of 10A on that 12v rail.

So would that be safe?

Has anyone done this before?

BTW I am getting a new powersupply, I'm asking all these questions for future reference incase something similar happens again and a new powersupply is out of the question at that time.
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Old 11-12-2012, 11:54 PM   #9
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Remember that reviewers' bench-mounted test systems may not include the high-end processors, large amounts of RAM, disk arrays, numerous cooling fans and multiple peripherals that a gaming PC will. The manufacturer of the video card will try to assess what type of system is owned my the majority of people to whom the card will be sold and then estimate power needs accordingly. Many of us, in turn, will add 30% to this figure to account for future upgrades and electronic degradation over the life of the system.
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Old 11-13-2012, 12:28 AM   #10
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When you start figuring out draw on the component level is when you add in the 30% safety factor number, plus you need to factor in peak loads on every item for example plugging in a usb device will momentarily draw more while the device starts up then while it is running normally.
This is also where the quality of the supply and the temp it was ratted at comes into play, good quality supplies are rated at continuous output over 40c, lower quality supplies are rated at peak output at 25c at temp they will not be running at unless kept in a freezer.
Will the card work on lower wattage supplies yes, work correctly and last as long as it should no.
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Old 11-13-2012, 03:37 AM   #11
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Modern computer systems use 12V power more than anything else. Cheap OEM PSUs still provide much of their power on 5V and 3.3V rails; voltages that are little used by modern systems.

Here are two examples: both of these are purportedly 450W PSUs but the first is a cheap OEM and the second a quality XFX.

OEM: +3.3V@28A, +5V@34A, +12V@21A, -12V@0.8A, +5VSB@2.0A

XFX: +3.3V@20A, +5V@20A, +12V@34A, -12V@0.5A, +5VSB@2.5A

Notice the huge difference at 12V; although both are sold as 450W units, the XFX provides over one and a half times the power where its mostly needed by modern computers.

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