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HD 7850 and recommended power

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December 4, 2012 1:23:54 AM

Working on a new build and im getting conflicting info on the what im gonna need to power my build.
Looking at it its pretty easy to see that its relatively power efficient

i3 3220 Ivy bridge...55w
Going with an H77 board. No OC.
2 x4gb of gskil ddr3 1600
blue ray drive/writer
7200 RPM 1TB HDD (may add a SDD for later on)
Haven't decided on a GPU but its either a 7770 or a 7850
Antec Case which comes with an Earthwatts 380Watt PSU

I know the earthwatts PSU are quallity power supplies so id like to stick with it

HD 7770 cars are very low power as they dont even require the separate 6pin power connector.

The 7850s require the additional power connection.......and on newegg a lot of the HD 7850 cards state they require a 450 watt psu in the specs.

Im looking at this build and i know a quality 380 watt psu is more than sufficient so am i good to go here or should i upgrade the psu. Would rather not since the dang thing came with a case.
Why would the manufacturer require a minimum psu without knowing your other components?? am i missing something

More about : 7850 recommended power

a c 109 U Graphics card
December 4, 2012 1:27:14 AM

Both require 6-pin pcie connector.
You can get by with that psu with both, if you have at least a single rail +12v 18A
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a b U Graphics card
December 4, 2012 1:27:28 AM

I would recommend about 500-550w if you just have one.
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a b U Graphics card
December 4, 2012 1:41:17 AM

mikeydee81 said:
Im looking at this build and i know a quality 380 watt psu is more than sufficient so am i good to go here or should i upgrade the psu. Would rather not since the dang thing came with a case.
Why would the manufacturer require a minimum psu without knowing your other components?? am i missing something

You're not missing anything, it's about margin of safety. Ideally, you should not exceed 80 percent of your PSU output or problems can start appearing. Since most system instability issues can be traced back to poor regulation, cheap internals, or under-performing power supplies, companies are more likely to state a requirement that's overkill to eliminate possible RMA's, damage from said issues, or false diagnosing of defective parts from them. A 450w PSU would be ideal here in order to cover grounds of all of your components, but the only proper way to test this if you have a PSU already is to use a plug-in watt meter. If you have a solid unit of say 85% efficiency, then if you pull 447 watts or (preferably) less from the wall on that 380 watt unit during a full system stress test load, you'll be fine.
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December 4, 2012 1:53:50 AM

djangoringo said:
Both require 6-pin pcie connector.
You can get by with that psu with both, if you have at least a single rail +12v 18A


I think the 12v rail is at 17A. Crap
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a c 109 U Graphics card
December 4, 2012 1:58:56 AM

You have dual rail if i'm not mistaken with both 17A, it should draw about ~300w the 7850 draws ~125w
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December 4, 2012 2:09:15 AM

matt_b said:
You're not missing anything, it's about margin of safety. Ideally, you should not exceed 80 percent of your PSU output or problems can start appearing. Since most system instability issues can be traced back to poor regulation, cheap internals, or under-performing power supplies, companies are more likely to state a requirement that's overkill to eliminate possible RMA's, damage from said issues, or false diagnosing of defective parts from them. A 450w PSU would be ideal here in order to cover grounds of all of your components, but the only proper way to test this if you have a PSU already is to use a plug-in watt meter. If you have a solid unit of say 85% efficiency, then if you pull 447 watts or (preferably) less from the wall on that 380 watt unit during a full system stress test load, you'll be fine.



I see what your saying and i agree. But im crunching the numbers and its looking well within those limits. The 7850...at its absolute max is around 145 watts. The Ivy i3 draws 55 watts. Throw in a HDD and a blue ray drive and i cant imagine eclipsing 250 watts. A couple more watts for a pair of fans and to power the mATX MB and ram and theres no way im passing 300watts. My brain tells me an efficient 380 watt PSU should suffice.

I also used a few psu calculators....i even used one on thermaltakes website and they gave me a number of 294. Its just bugging me they state a minimum PSU of 450
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December 4, 2012 2:38:13 AM

djangoringo said:
You have dual rail if i'm not mistaken with both 17A, it should draw about ~300w the 7850 draws ~125w



ok your correct...its got 2 rails at 17A. The total rated Max A for both rails combined is 25.
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a b U Graphics card
December 5, 2012 8:46:33 PM

mikeydee81 said:
I see what your saying and i agree. But im crunching the numbers and its looking well within those limits. The 7850...at its absolute max is around 145 watts. The Ivy i3 draws 55 watts. Throw in a HDD and a blue ray drive and i cant imagine eclipsing 250 watts. A couple more watts for a pair of fans and to power the mATX MB and ram and theres no way im passing 300watts. My brain tells me an efficient 380 watt PSU should suffice.

I also used a few psu calculators....i even used one on thermaltakes website and they gave me a number of 294. Its just bugging me they state a minimum PSU of 450

I'm not disagreeing with you one bit. This is the PSU that you have and doesn't appear to be of inferior quality. Wattage is only part of the equation as I'm sure you've heard that amperage is where it is at. The problem here lies with the fact that you will be so close by the numbers that whose to say what your PSU will be up to the task of when system utilization pegs 100% for an extended duration. I think it should work. Testing this with a watt-meter will let you know how much of a margin of safety you will have - but believe that it will be close. If you do choose to overclock things though, then I wouldn't question if this PSU would be capable of running your system, I know it wouldn't then. If it did, I would almost guarantee that voltages would be a little erratic and dropping below safe values if pushed hard - and this is where problems pop up. In stock form, I don't think you should run in to problems. Real-world testing through stress-testing and verifying actual power consumption would tell you exactly where you stand - and that's free compared to buying a bigger PSU that you may not even need.
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December 5, 2012 9:21:39 PM

matt_b said:
I'm not disagreeing with you one bit. This is the PSU that you have and doesn't appear to be of inferior quality. Wattage is only part of the equation as I'm sure you've heard that amperage is where it is at. The problem here lies with the fact that you will be so close by the numbers that whose to say what your PSU will be up to the task of when system utilization pegs 100% for an extended duration. I think it should work. Testing this with a watt-meter will let you know how much of a margin of safety you will have - but believe that it will be close. If you do choose to overclock things though, then I wouldn't question if this PSU would be capable of running your system, I know it wouldn't then. If it did, I would almost guarantee that voltages would be a little erratic and dropping below safe values if pushed hard - and this is where problems pop up. In stock form, I don't think you should run in to problems. Real-world testing through stress-testing and verifying actual power consumption would tell you exactly where you stand - and that's free compared to buying a bigger PSU that you may not even need.



Newegg has a kil-a-watt plug in meter on sale. 16 bucks. I just ordered it so ill go ahead and take ur advice and see how things look. Thanks
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December 5, 2012 9:22:03 PM

Best answer selected by mikeydee81.
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