7770 and 650Ti 12v rail Amps compared to my PSU

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solvectro

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Hey guys I just need some advice regarding my PSU and potential GPUs.
My system specs are:
Intel i5 3470
Gigabyte ga-b75m-d2v
8gb ram G.skill ripjaw
Seagate 500gb HDD
ISO 500PP 420w

The specifics on the PSU are:
420Watt
1x SATA
1x 20+4 Pins
4x 4 Pin Molex
1x Floppy Drive
1x 12V Processor

+3.3V 22.0A
+5V 36.0A
+12V 18.0 A
-12V 0.5A
-5V 0.5A
+5sb 2.0A
Because this is a cheap PSU, it actually has lower specs then its listed, about 16A on its 12v rail according to another site.

I've been reading about and it seems the most important thing is the Amps on your 12v rail. I dont know the Amps on the 7770 or 650Ti.
So would this PSU be able power either a 7770 or 650Ti? If so which would be easier to power for this PSU?

Thanks alot for any help :)


 
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toyftw
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Xttony

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Both the cards you specified need about 75watts to run and if the PSU can really supply 16AMPs then you are on th safe side. Anyway 75watts is very low and I think even a bad quality PSU can provide it.
It is not advisable to have a bad quality PSU as it can give voltage spikes destroying any component.
 
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vaughn2k

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Sapphire are great designers of AMD cards, I have a lot of experience with them (all 5 of my cards, including the firepro) are all Sapphire. If you can get HIS, then much better, but quite expensive...
 
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solvectro

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solvectro

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I dont live in the US so ya... and I dont think my PSU will handle 650ti really well.. cheers though
 
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Xttony

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Any graphics card that you put will be powered by the power supply eventually even when it doesnot require a power connector. People have successfully installed and used the card even on a 280watts PSU so I think your PSU will handle it.
I know the recommended power is 500watts but it doesnot matter as long as there are no voltage fluctuations caused by a bad PSU.
 
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nukemaster

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It would appear that the Sapphire has Display Port out so it should be able to drive 3 screens if needed while the gigabyte has its HDMI and DVI linked(so 2 screens tops).

I would keep an eye out for a power supply in the future for sure. Yours seems to be an older design. This is why it has such a low percentage of its power dedicated to the 12 volt rail.

I have a GTX 650 ti(paired with a i5 750) on a 300 watt power supply, but it has 22 amps @ 12 volts(264 watts) vs 16-18(192-216).

Your system is NOT power hungry by any means, but it is always good to have some reserve power and even more important with older/cheaper designed power supplies.
 
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solvectro

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I consider my PSU to be pretty cheap so dont really wanna take a risk. So i think atleast with a 7750 the demand on the PSU is even less so risk of any damage would also decrease. :??:
 
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Xttony

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Why don't you just buy a new power supply? Saving some money won't do you any good if the PSU ends up damaging your computer and trust me if tht ever happens the cost will be much more than what you pay for a new PSU.
 
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solvectro

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Im not too familiar with PSU stuff but is the entire +12v rail dedicated to the GPU and CPU? So for my PSU +12v rail it has about 16amps-18amps (192w-216w) allocated for GPU+CPU usage?
 
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nukemaster

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Older systems used to use more of the lower rails and the 12 volt rail was just for things like hard drive/CD drive motors, fans and some onboard parts. Some video cards took power from the 12 volt rail by way on an old LP4(hard drive/cd drive power plug)

As time went on, many things moved over to using the 12 volt rail. On modern systems, the CPU/GPU as well as many other parts are running off 12 volts(while they covert it down to a lower voltage needed).

Its all about wire size. You can carry MORE power(wattage) at a higher voltage on a smaller wire. So lets say a cpu takes(this suckers a power hog :) ) 150 watts.
150 / 12 = 12.5 AMPS. The cpu it self only runs on 1.1-1.5 volts(the board will turn the 12 volts into the needed voltage.), BUT you still need to be able to get the needed power to it.

Lets say you wanted to get that power from the 5 volt rail.

150 / 5 = 30 AMPS. So you need BIGGER wire(if you try to use smaller wire, it can burn)

Lets try to get 150 watts @ 3.3 volts.

150 / 3.3 = 45.4545454545..... AMPS. We are getting onto some big wire.

Now if you look at power lines you may also notice long distance runs are done with much smaller wires at VERY high voltage then dropped down to your household power(120/240 depending on location) at a sub station or transformers on power poles.

Ever wonder why some car wiring is much bigger? low voltage so more amps needed to get the same amount of wattage. (it would take 156.25 amps to get as much wattage as a normal 15 amp outlet @ 120 volts(Canada Standard plug) on a 12 volt system)

Some things do still run on the 5 volt rail. ALL usb devices that take buss power, parts of the hard drives and optical drives as well as all 2.5inch SSD drives(or laptop drives). While SATA has 3.3 volts, I have yet to see a drive NEED it to run.

Either way, with more and more on the 12 volt rail. Power supply makers beefed the 12 volt rail up and generate the 3.3/5 volt rails from small DC-DC converters. So whatever 3.3 and 5 you need can actually be taken from the 12 volt rail while still allowing LOTS of 12 volt power for parts that need it. This is why you can NOT add up all rails and have it make sense. They list combined rail ratings for multiple 12 volt rails as well as the 12 volt rail + 3.3/5 volt rails.

Ok, I think I have said too much.
 
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toyftw

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Hi - 16a on the +12v won't cut it. 650ti needs 20a & 7770 needs 19a.

So, your best bet is the 7750 if you can't upgrade your psu.

Tom

Quite honestly, in your situation I'd upgrade the psu 1st, and then
get a new gpu when you can afford to.


 
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solvectro

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Haha thanks for the essay nukemaster, I think I understand abit better now.

Atm if i buy a GPU, the 7750 seems to be the safest and best option for me. I use a 1440x900 display so I dont think ill be demanding much GPU power.

The games im aiming to play are probably LoL, Dota 2, Skyrim, AC3, Planet Side 2 and some MMORPGS at high/near max settings.
Do you think the 7750 can handle it?
 
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