How many amps do i have on my 12v rail?

bradderzd1994

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I just got a radeon 6870 but i don't know if my psu can handle it?

On my psu it says 450w and it has 12v1 18max and the other says 12v2 16max.

Do i have to add these up or something? Do i need a better one for my GPU and how many amps does my GPU require
 

clutchc

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The HD 6870 should draw about 13A @ 12V (155W/12V) when maxed out.
http://forums.atomicmpc.com.au/index.php?showtopic=264

The 2 6 pin PCIe connectors on a PSU w/2+ rails should come from opposite rails, so you will be sharing the load between rails. However, If your PSU has only one 6 pin PCIe connector, it may not be rated to handle that kind of load. If you use the twin Molex to PCIe adapter provided to gain another PCIe connector, the card will function fine. But at extreme power draw, you may experience freezes or shut downs. That will be a dead give-away that your PSU is under rated.
 

What is the make/model of the PSU? Does it list a continuous load rating? A lot of cheap PSU mfrs will list their max rating instead of continuous operation rating to slap liar-labels on them and sell them for more money.

What are the rest of your system specs? Are you doing any overclocking?
 

bradderzd1994

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I have a LiteOn PS-6451-5 i dont know if it has a continuos load rating. I don't do any overclocking. I have an i5-650 3.2ghz,
4gb ddr3 ram, hd radeon 6870, 500gb hdd
 
Does the PSU label list the combined total power available on 12V1 and 12V2? If yes, then divide that number by 12 and that is the max amperage available on the 12V rails. Are you currently using this PSU in your system with the 6870? If yes, then is the system stable? If no, then you should get another PSU. If yes, then you can use your current PSU.

Didn't we already answer this question for you in another thread?
 

bradderzd1994

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On the label it says 12v1 20A and 12v2 18A (they both say max next to them) so how would i divide that by 12? it would end up being not even 2 amps? And i don't know my system feels a little bit slower when trying to open multiple tasks and switching between them.
 
You wouldn't on the label to the right of where it lists the amps for 12V1 and 12V1, there is another box that says watts max. I think it says 260W, but I can't read the label clearly here:
http://www.plugloadsolutions.com/psu_reports/LITE-ON_PS-6451-5_ECOS%201900_450W_Report.pdf
You divide the max watts by 12 and that is the max amount of amps on the 12V rails. If that number is 260W, then the max amps is 21.7A. Simply adding the 20A from 12V1 and the 18A from 12V2 does not tell you the max amps on the two rails.
 
If the max watts on the 12V rails is 260W, then the max 21.7A is insufficient to run your system at full loads and will cause stability issues such as reboots or shutdowns.
 





Hard to guess if it changes like that

Label shows 360 watts combined
liteon450.jpg
 
Thanks for the assist Dell.

Brad: 360W means that the PSU has 30A on the 12V rails; it is technically insufficient to run an hd6870 and if you were buying a PSU, then I would recommend a PSU with at least 32A on the 12V rails. That being said, if your PC is running stable and the noise/heat levels are ok in your PC during heavy operating loads, then you should be able to continue using this PSU.
 

bradderzd1994

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I think my PSU is 450W
 
Yes it is, but it can only deliver 360W (30A) on the 12V rail and that is the rail where PCs draw 80% of their power from.

Like I said before, a system with an HD 6870 should have a PSU with at least 32A on the 12V rails. Amperage on the 12V rail is more important than the total watts that your PSU can deliver when determining whether or not a PSU is sufficient for a certain CPU/GPU setup. That's is because the CPU/GPU get most of their power from the 12V rail. Your system with 30A on the 12V rails is just under the required spec. If your PC is stable, then keep using your current PSU. If it gets unstable during heavy loads (gaming for instance), then the first thing that I would suspect is the PSU.
 

bradderzd1994

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Sorry for the constant problems but would any of you be able to link me to any decent PSU's preferably not over the £40 mark
 
Not a problem at all!
In your budget:
XFX 450W: http://www.scan.co.uk/products/450w-psu-xfx-pro-core-edition-p1-450s-u2b9-85-eff-80-plus-bronze-sli-crossfire-eps-12v-fan-atx-v231#ProductFeatures
This PSU has 34A on the 12V rail and one 6+2 pin PCIe power connectors and is electrically sufficient for your build. Excellent PSU made by Seasonic for XFX, 5yr warranty, rock solid rails, quiet. You will have to use a molex to PCIe adapter for the second PCIe power connector.

A little over your budget:
1. XFX 550W for 48quid: http://www.scan.co.uk/products/550w-psu-xfx-pro-series-core-edition-p1-550s-ukb9-85-eff-80-plus-bronze-sli-crossfire-eps-12v-fan-at#ProductFeatures
2. OCZ ZS 550W: http://www.scan.co.uk/products/550w-psu-ocz-technology-zs-series-ocz-zs550w-uk-86-eff-80-plus-bronze-sli-crossfire-eps-12v-quiet-fa

You don't have to get a new PSU as long as your system is running ok on your current PSU. If you decide to get another PSU, then I would save up a little bit more money and get the XFX 550W.
 

bradderzd1994

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My GPU requires 500W so i was thinking of getting either of these, (i've found somewhere else i can get them cheaper)

http://www.amazon.co.uk/OCZ-OCZ-ZS550W-UK-Series-Bronze-single/dp/B005DJJTFA/ref=sr_1_2?ie=UTF8&qid=1338128965&sr=8-2

http://www.amazon.co.uk/XFX-550W-Power-Supply-Edition/dp/B005TDTV0S/ref=sr_1_1?s=computers&ie=UTF8&qid=1338128993&sr=1-1

Which would you say is best? I was lurking towards the XFX for the more amps
 

First of all a psu upgrade is hardly ever a bad thing, I'd go for the XFX

There's a big difference between what manufacturers reccomend and what is actually required

Lets use the GTX460 as an example
http://www.geforce.com/hardware/desktop-gpus/geforce-gtx-460/specifications

160w rated max board power compared the the 151w rating for the Radeon 6870
450w reccomended psu compared to the 500w reccomendation for the 6870 ( Hmm, higher rated power, lower power reccomendation, what's up with that ? )
Both cards have been used in Tom's value builds with a 430w/32a psu without causing undue stress on it ( I benchmarked my ENGTX460TOP in a dual core system with a 375w/30a Dell psu, didn't even cause it to heat up )
If your system is running without issue there's no need to rush to buy a new psu
 

bradderzd1994

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I feel like my system is being stressed. All the time when doing anything it such as opening and closing programms or loading a page or playing a game it will freeze for like less than half a second. I know it's not much but if feels like it's being stressed.
 

This is more like a CPU issue, and may or may not be associated with the PSU.
 

bradderzd1994

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I have an i5-650 though and this is surely on par with my graphics card (radeon 6870)
 

jim45682

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While I know that what the manufacturer recommends and what is actually required are different, and there are proven cases of systems running on PSU's that technically they had no business running on, with the possible repercussions of you choosing wrong and the PSU going out and frying your system just to spite you, I always choose to err on the side of caution and roll with a quality PSU of at least the minimum recommended power or more. Worst case you have more PSU than you really need but its set for future upgrades.