How much overhead should by PSU have?

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pteradox

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Feb 3, 2013
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I'm planning on revamping my system with a new case, CPU, and motherboard. Here are the relevant specs:

Radeon HD6870 GPU
Intel i5-3570k processor
ASRock PRO3 motherboard (Intel Z77)
Two SATA hard drives (fairly low-mid range so total power should be ~15W I think)
2x 3GB memory sticks, up to 4 sticks potentially
4 or 5 USB devices
Up to five internal fans (4x 120mm, 1x 140mm), though I doubt I'll need them all. One has an LED I can turn off.
Speakers which I never use or keep on

I have a 550W power supply. Looking up the power consumption of each piece (or an appropriate approximation) under load, I found the total to be somewhere in the range of ~520-530W (please, if you can, crunch the numbers again if I'm wrong).

a) Is that calculation accurate? (This website only gives me 410W which seems very low) Can anyone with a bit more know-how on component power consumption verify that number?

b) How much overhead should a power supply have under estimated load? Is ~20W enough or should I consider dropping $120 for a 700 or 800W supply? (The one I have now is jerry-rigged and therefore probably unsellable, so I have reservations about upgrading).

c) If push comes to shove, can anyone recommend a (good) budget power supply with at least 650W? This one seems pretty okay for the price.
 
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Ooh, a Logisys PSU-shaped object. That's among the worst ..."devices" you could buy. If you're lucky, it might be good for 300W, but possibly not cleanly. Do NOT deliberately overload it. A good PSU has protection circuits and will shut down gracefully, a device like that will most likely self-immolate, and may take other parts into the fiery abyss with it.
The Rosewill you linked got a good review at HardwareSecrets. There are better units out there, but that one is good. The Rosewill Capstone units are a little more modern, even more efficient, and some are modular.
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Ideally you want to put your PSU in the 30%-80% draw range. This is where modern PSU's tend to be most efficient in power regulation. You would not need any more than a quality 600W PSU for what you are showing there (which, with just of the cuff calculations I would estimate ~75% draw). I think your 500W is close to it's maximum output I would think your PSU would be loud a lot of the time (especially while gaming)
 
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As to what you need, the 410W figure sounds reasonable. I have a HD7970 in a machine with a 65W TDP CPU that is bitmining 24/7. The GPU is running flat out (96%+), but my UPS shows a load of ~310W-321W (including monitor; a Kill-a-Watt shows 340W, which also seems reasonable). Unless you're skeptical about its quality, your existing 550W PSU is easily sufficient. Otherwise, XFX Pro-series PSUs are made by Seasonic, so they're good. Depending on your upgrade plans, 450W would be enough, and 650W would allow for multiple graphics cards.
 
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My current PSU has held up fairly well. It gets a little hot at times (currently using a stock Intel motherboard and an i3-550 CPU with about the same power consumption as the i5-3750k), but the case I'm getting has a ton of fan slots so maybe I could share the load and get some better circulation. I'm not worried about idle usage, just usage under heavy load.

Here's a better question: would it be unsafe to try it anyways and see if the system fails? If the power supply is overtaken then it will just short out and cut the system off, right? Is there any danger to components?

What EXACT PSU do you have? That will make a huge difference.
Click to expand...

This one. Looking back I should have gone with a better known brand but it works if nothing else. That being said, looking at more recent reviews it doesn't seem to hold up incredibly well...

 
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Yes there is a danger to the components. What is your PSU model?

Ah i see you edited it in...

Yes that is the best of junk, get a new one... LOL. Do you have a budget in mind?
 
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After consideration and reading reviews it looks like my 550W supply is more or less not actually rated like such. Maybe I'll have to swing for a new one. Can anyone make any suggestions? I could pick up this one for only $50 with a coupon.

Do you have a budget in mind?
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I'd like to keep it in two figures or not much over that. I never really planned on revamping the power supply, I guess I just didn't think much of it. Toss out some suggestions if you can and I'll go from there.

I'm really thinking about the Rosewill one. It's only $50, doesn't seem like a ripoff, and should provide enough wattage. I'd rather not drop $110 for an XFX supply - quality is good but if it does its job adequately I'm not too worried. But judging by my last purchase I think it's quite clear I'm not all too keen on the ins and outs of power supplies so a second opinion would be great.
 
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For a starter your system should be around 300 Watts when running a high end game, NO more than say 350 Watts.
PSU:
1) If possible buy a PSU listed as a tier 2 PSU, BUT no lower than Tier 3.
… Poor quality PSUs, over rate capabilities by rating at ambient not 40C which quality PSUs rate their out at. Ie Low quality PSUs as they heat up can only provide 60->70 % of rated value.
… The +12 V ratings are more important than total wattage. The majority of the power is derived from the +12 V rail – IE Your GPU and CPU.
… General guide lines I use. At Idle (175W), then MAX should be (173/.2) = 875 Watts. Then look Max load (for a single 6870) would be Larger than 300 W divided by .7 = 428 Watts NOTE the +12 V should be at least close to 300/12 = 25 Amps. 875 Watts is way over kill, so 20% at Idle not an issue. A “quality” 450 with say 30 Amps on +12 V rail would work fine for a single 6850, a Quality 500 would provide more wiggle room. IF Crossfire may be considered downstream, then a 650 Watt would be an ideal choice

Ref: http://www.guru3d.com/articles_pages/radeon_hd_6850_6870_review,10.html
Extract from link
Our test system is based on a power hungry Core i7 965 / X58 based. This setup is overclocked to 3.75 GHz. Next to that we have energy saving functions disabled for this motherboard and processor (to ensure consistent benchmark results). On average we are using roughly 50 to 100 Watts more than a standard PC due to higher CPU clock settings, water-cooling, additional cold cathode lights etc.
Measured power consumption - 6870
1. Advertised TDP = 150W
2. System in IDLE = 173W
3. System Wattage with GPU in FULL Stress = 295W
4. Difference (GPU load) = 122 W
5. Add average IDLE wattage ~ 19W
6. Subjective measured GPU power consumption = ~ 141 Watts

My system i5-2500K OCed to 4.6 loaded by running Furmark (Higher Power consumption than a game).
With 2 HDDs, 2 SSDs, 16 Gigs of Ram, a Blu-ray writer. My Max power consumption pretty much matched the above test system – I drew less than 350 Watts. This was measured @ the wall. Factor in PSU eff and system power calculates out to approx. 280 Watts.

Bottom Line: For a Single 6870, a “Quality” 450 Watt PSU would be better than many of the 500->600.
Xfire pair of 670s then 650 Watt would be a great choice.
If considering Crossfire with a pair of 6870s then go for a 650 Watt quality PSU.

ADDED, Link to tier rainings:
A little dated: http://www.overclock.net/t/667515/reference-power-supply-tiers
 
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Ooh, a Logisys PSU-shaped object. That's among the worst ..."devices" you could buy. If you're lucky, it might be good for 300W, but possibly not cleanly. Do NOT deliberately overload it. A good PSU has protection circuits and will shut down gracefully, a device like that will most likely self-immolate, and may take other parts into the fiery abyss with it.
The Rosewill you linked got a good review at HardwareSecrets. There are better units out there, but that one is good. The Rosewill Capstone units are a little more modern, even more efficient, and some are modular.
 
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Solution
Bottom Line: For a Single 6870, a “Quality” 450 Watt PSU would be better than many of the 500->600.
Xfire pair of 670s then 650 Watt would be a great choice.
If considering Crossfire with a pair of 6870s then go for a 650 Watt quality PSU.
Click to expand...

I'd like to keep the door open for upgrades. So I may not need a 650W supply right now but if somewhere down the road I decide to invest in a bigger GPU, Crossfire, overlocking, or just decide to run a bunch of fans in my case I think it couldn't hurt. That's why I'm iffy about anything below 500W. As far as quality goes, I really just need enough connectors and one that isn't going to crap out on me when I boot up the latest and greatest games.

The Rosewill you linked got a good review at HardwareSecrets. There are better units out there, but that one is good. The Rosewill Capstone units are a little more modern, even more efficient, and some are modular.
Click to expand...

Maybe, but twice the money. As long as this Rosewill isn't as shady as the one I have right now I think I'll be okay.
 
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HWSecrets... Ahhhh their PSU reviews bring tears to mine eyes... There of VERY few sites that do it as well as they do.
 
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Here are the two I'm looking at right now. The Rosewill Green Series at $50 ($65 - $15 discount), or the Corsair TX Series at $89, but with a 10% discount as well as $20 mail-in rebate. That'll bring it to about $14 more after shipping, which (if it is noticeably better) is a small sacrifice. Thoughts?

The two biggest things to me (besides being able to run and not burn my tower to the ground) are noise levels and perhaps temperature (mainly noise levels). I suppose the Corsair has a pretty lengthy 5 year (limited) warranty but I think if it's going to crap out due to manufacturer error it'll be in the first two years for certain.
 
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I'm sure it's worth the price but the bottom line is $90 (or $80 after rebate) is just too much for me (considering the alternatives), and I don't need 850W either. I'm already buying a new case, processor, and motherboard so I'm well over $300 even if I can sell my old i3 for a decent price.

After reading the Corsair TX rebate option a bit more I found out it isn't something I'm too interested in (they send you a prepaid card in the mail, there's a monthly maintenance fee, etc.). I think I'll just go with the Rosewill - I know it isn't a prestigious brand but this product itself has good reviews and in the end that matters the most.

Thanks for the pointers though. If I hadn't investigated the power supply I could very well have plugged everything in and found my crappy excuse for a power supply blowing on day 1.
 
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After rebate it 10$ more than the one you were looking at and has no shipping cost, so 7$ dollars more for a nice improvement.

A PSU is the cornerstone of a good build, do not underestimate a good PSU.
 
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