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Author Topic: The PSU Mystery  (Read 992 times)
Axez D. Nyde
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August 04, 2011, 09:19:47 AM
 #1

Hey there!

Something weird happened to me when setting up my very first miner. I had a leftover mainboard and CPU, also a HDD and a case, so I figured if I popped in a new Grafix-Card and a PSU I could mine away...

I calculated the power consumption of the whole system and came out with ~340 Watts. So I bought a 350 Watt PSU (Xilence Rev. 3).

But when I had everything in place, OS installed (WinXP 32 Bit) and phoenixminer set up, the power consumption went to >380 Watts. (I had a Watt-Meter at the power plug of the PSU.)
I thought it would be okay that the PSU went higher than 350 because of course it only has an efficiency factor of ~85%, so to supply 350 Watts it might need 350 / 0.85 = 411 Watts. But after two hours getting hotter and hotter, it blew. Whoooops!

I then bought a 450 Watt Thermaltake PSU and it's running at <320 Watts now.

Also, I had the Xilence PSU replaced so would it be wise to put it back in and think of the first PSU as construction error or something?
Can someone explain what happened?

Thanks in advance!
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SMOKEU
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August 04, 2011, 10:13:56 AM
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You should not load your PSU anywhere near the rated output for any great length of time! It's OK if you go near the rated output for very brief periods of time, but in general you should always buy a PSU that's AT LEAST 20% bigger than what you actually need. I wouldn't trust those Thermaltake PSUs either, the Toughpower range are OK but the rest are pretty cheap quality. Cheap PSUs in general put out a fair bit less than their rated wattage. High quality PSUs often put out slightly more than their rated wattage.

I suggest you look at a high quality PSU like one from Corsair or Seasonic. If your system is using 380W then I suggest a minimum of a high quality 450W PSU. Remember that PSUs lose efficiency at high loads, so you'll be paying a lower power bill by having a PSU that's a fair bit bigger than what you need as you won't be loading it much in comparison to a PSU that's under a very high load.
Axez D. Nyde
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August 04, 2011, 10:25:20 AM
 #3

Yeah so I guess I'll be sticking with the Thermaltake PSU because my wallet.dat is very small right now Cheesy

How can I tell a good from a bad PSU? To me they're all the same
Roland68
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August 04, 2011, 10:34:53 AM
 #4

They are NOT the same ... check for A SINGLE 12V RAIL ...that is what your graphic card need ... 3v or 5v are nor relevant for mining ... avoid PSU with multiple 12V rail like 3x15 Amp .... prefer a 50 Amp single rail ... it-s written on the PSU, on the box, and in the specs ...
Axez D. Nyde
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August 04, 2011, 11:13:36 AM
 #5

Hmm, can you explain why a single rail 12V is better than multiple?
Xephan
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August 04, 2011, 11:49:08 AM
 #6

Also, I had the Xilence PSU replaced so would it be wise to put it back in and think of the first PSU as construction error or something?
Can someone explain what happened?

How much did you pay for the Xilence? One of the common plagues in PSU market is cheap brands often use misleading labels. They get the factory to make a 300W PSU for example but slap a 350W or even 400W label on it. What they figure is most users won't use that much power so 90% of the time, they are going to get away with it.

Tough luck when the user happens to be pushing the GPU 100% 24/7 Cheesy

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BombaUcigasa
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August 04, 2011, 11:52:52 AM
 #7

Hmm, can you explain why a single rail 12V is better than multiple?
He doesn't say having [just] a single 12V rail...

He says you need to have a single 12V rail with a higher current rating, for your GPU. Instead you have multiple rails with divided power, whereas your GPU consumes 3x-10x more power than any other PC component needs.
Roland68
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August 04, 2011, 11:54:29 AM
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Hmm, can you explain why a single rail 12V is better than multiple?
This question seem ridiculus to me ..but ok ... lets say each of the 3x 12 volt rail gives you (12*15amp=180watts) how would you power your card (maybe overclocked) eating for example 200-250 watts ... the second and 3 rail going nowhere ...

with a monorail of (example) 50A you get about 600watt ..enought to feed your card ...

but continue to experience with cheap PSU ... before you move to corsair , thermaltake, or other single rails ...
Xephan
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August 04, 2011, 11:55:20 AM
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Hmm, can you explain why a single rail 12V is better than multiple?

Multiple +12V rails came about due to safety considerations about 5 years back due to an IEC recommended limit of 240VA per wire. For a +12V line, this mean no more than 20A. However as power requirement grew beyond 240VA for the +12V line, the option was to offer multiple +12V rails.

This lead to another problem when a single component like the GPU starts to burn insane amount of power. Depending on each +12V rail was allocated, you get this annoying problem of over-current protection kicking in when the total draw on a +12V line crosses 240VA or whatever was the limit on that particular rail.

After a few years, Intel decided to quietly drop the IEC recommendation and manufacturers started making single +12V PSU again so that the hardcore uses won't face the over-current problem again.

Of course the risk now is that you could get a situation that pumps an insane amount of power through a low resistance (but not low enough to be considered shorted) fault that starts melting the board or something.

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Axez D. Nyde
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August 04, 2011, 12:01:59 PM
 #10

but continue to experience with cheap PSU ...
There's a reason this is the newbie Forum. No need to get cocky.

So what one could use best is a single rail supplying enough VA's for the GPU and another smaller rail for the rest of the components?
Roland68
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August 04, 2011, 12:09:50 PM
 #11

you right ... but one psu is enought ... 3.3v and 5vare allways ok even in a single rail config ..your single rail psu gives you goos power on the 12v line AND 3.5 AND 5V ..don't worry about this ...
Axez D. Nyde
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August 04, 2011, 12:14:38 PM
 #12

Okay then.
I will just stick with my Thermaltake 450 W PSU for now and as soon as I need more power I will make sure to get a single rail thingy, now that I know to look out for that in particular.

Thank you all!
vinas
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August 04, 2011, 02:11:52 PM
 #13

ATX switching PSU's are only recommended to be ran up to a maximum of approximately 85% full rated load.

Also I can't be bothered to explain the differences in ratings, but you can assume if it's a cheap brand that it will not output what they claim (wattage will be lower).
mountainminer
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August 04, 2011, 06:13:37 PM
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It's not overly surprising that a cheaper power supply popped after running at full load continuously for 2 hours. You can see by looking at this link of 80 PLUS ratings that 50% of rated load gives you optimal efficiency.

http://en.wikipedia.org/wiki/80_PLUS#Efficiency_level_certifications

Running a power supply beyond 80-85% of it's max rating continuously is inviting trouble. Here's what I would do. Add up the power consumed by your GPU cards and CPU, then round up a bit to account for the motherboard, RAM and fans. Then add 2 zeros onto the end of that figure and divide by 50, 60, 70, 80, whichever percentage of efficiency you'd like to achieve with your power supply. That will tell you how many watts you need.

Here's a chart I downloaded from somewhere that shows how much power the various GPU cards require, in addition to megahash rates, etc...

http://i93.photobucket.com/albums/l59/lytlesnake/VhgVh.gif

I think the (80 PLUS/Bronze/Silver/Gold) power supplies are great if you want to spend the money. But remember, you can also apply the 50% Max Efficiency rule to cheaper power supplies, which is probably ideal if you're trying to build an overall cost effective miner. By overall cost effective, I mean striking a balance between initial cost and electrical efficiency. Then again, probably a majority of modular PSU on the market have an 80 PLUS rating at this point anyway.
Axez D. Nyde
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August 05, 2011, 08:12:10 AM
 #15

I followed the wikilink you supplied and landed at the homepage of the 80 plus certification where I found a datasheet of the 350 W PSU that popped.

http://www.plugloadsolutions.com/psu_reports/XILENCE_XP350.(12)G_ECOS%201752.1_350W_Report.pdf

When I look at the input-output diagramme it clearly states that it needs about 400 W to supply 320 W.

Also in the wiki it says
Quote
In some instances a reseller has claimed a higher wattage than the supply can deliver - in which case the reseller's supply would not meet 80 PLUS requirements.[4] The 80 PLUS web site has a list of all certified supplies, so it is possible to confirm that a supply really meets the requirements
Which sounds to me like every 80 PLUS cvertified PSU should be able to deliver the wattage that is written on its packaging, right? So my 350 W PSU should supply 350 W without blowing.
Gerken
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August 05, 2011, 01:10:58 PM
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Yes it should.  And those 1000 watt amps you see at walmart for 80 bucks should be able to push out 1000 watts but they don't.  PSU's are not intended to run at 100% load for hours on end.  Get a good one next time; Corsair, Seasonic, Antec are all good brands.  Coolermaster, Thermaltake, Rosewill and the like are just asking for trouble in a power hungry setup. 

Xephan
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August 05, 2011, 06:37:00 PM
 #17

Which sounds to me like every 80 PLUS cvertified PSU should be able to deliver the wattage that is written on its packaging, right? So my 350 W PSU should supply 350 W without blowing.

Should and does are two different thing. There are ways to get certified/reviewed well yet sell crap. The practise is common enough to have its own name: http://en.wikipedia.org/wiki/Golden_sample

That is why 80Plus has a procedure where a member can challenge that another manufacturer isn't adhering to the tested standards. But it costs quite a bit of money and nobody wants to rock the boat because everybody knows almost everybody has a model or two which are targeted at low price market segments and marketed above factual ratings.

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mountainminer
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August 05, 2011, 07:33:40 PM
 #18

I followed the wikilink you supplied and landed at the homepage of the 80 plus certification where I found a datasheet of the 350 W PSU that popped.
Glad I could be of some assistance.

A Bronze-rated PSU at 50% load achieves 85% efficiency, which is about the same as a Silver or Gold at or near 100% load. The difference is, the Bronze costs less and will probably last longer if ran conservatively. Mining places a continuous load (as in "24/7") on the power supply and graphics cards, which is not the same as "average computer use". So having an adequate power supply is a must, and a little overkill is recommended.

Also if you're running at only 50%-70% load, you don't have to worry about whether the PSU is single-rail or multi-rail so much, as you won't be putting stress on it. You don't have to buy a Gold-rated power supply to be efficient. They are nice though.

PSU's are not intended to run at 100% load for hours on end.  Get a good one next time; Corsair, Seasonic, Antec are all good brands.  Coolermaster, Thermaltake, Rosewill and the like are just asking for trouble in a power hungry setup. 
I'd like to add Enermax to that list. I've had one for years and it's rock solid.
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