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Author Topic: Power Supply Calculations  (Read 4322 times)
conspirosphere.tk
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December 21, 2011, 05:28:54 PM
 #1

I am planning to install a Radeon HD 5830 + a Radeon HD 5750 in one of my rigs, which has a Cooler Master rs-500-psap-j3 PSU
At the moment this system runs fine mining 24/7 with a Radeon HD 5870 @965/300

From this PSU calculator http://www.thermaltake.outervision.com/index.jsp I get that the "Recommended PSU Wattage: *" is 365W, which sounds feasible for my PSU.

Alternatively, since I am too bankrupt for an high end PSU, I think that I might use an old Codegen 400w that I have running around to power a Radeon.
What do you think?

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December 21, 2011, 06:35:31 PM
 #2

Stay away from Codegen, you risk frying some or even all of you components, also avoid PSUs from this list (it is not complete):

Akyga, Altis, Aspire, Aton, Bestec, Coba, Codegen, ColorSit, COMPAQ, Computer, Deer, Eurocase, Everpower, Feel, Fever, Four Star, Gembird, Gigabajt, Hawk, Hec, Impet, i-box, Incore, Levicom, Linkword, L&C, Logic, LOGISYS, Megabajt, Mercury, Metropilis, Mustang, Newton Power, Platin Power, Power Color, Powercomp, Power Man, Procomp, Octigen, QTECHNOLOGY, Q-tec, RAIDMAX, Rubikon, Ropla, Sansun, SilenX, Sun Pro, Suntek, Take Me, Task, TE, Tracer, Tronje, Ultra Media, V Power, Win, Xilence, XION, X-Power, 2N

also from this list:
http://www.tomshardware.co.uk/forum/299096-10-blacklist

if you are unsure, google for reviews, jonnyguru.com is a good resource of extensive PSU reviews/tests

these are examples of good PSU brands:

Amacrox, Antec, Astec, be quiet, Chieftec, CoolerMaster, Corsair, Delta, Enermax, Enlight, OCZ, PCPower&Cooling, Pentagram, Seasonic, Silver Power, Tacens, Tagan, Topower, Yesico, Zalman

but there are worse lines from time to time so always do some google search

Dont want to go on too much details about the differences between cheap and expensive ones but the chinese crap increases your chances of frying one or more components (inadequate or no protection against overcurrent for example), not to mention increased power bills because cheap PSUs will be very inefficient (only look out for PSUs that are at least >80% efficient)

For those 3 GPUs I'd recommend +650W PSU
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December 21, 2011, 06:45:16 PM
 #3

Save yourself the trouble and just get a Corsair AX-series.  Any of them.

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December 21, 2011, 07:27:20 PM
 #4

I have had great luck with Kingwin,just read the reviews before buying.As with any company,some models just suck.

Rule of thumb(mine) "always have a 200 watt buffer".If you need 365 add 200=600 watt(rounded to next highest).It'll run cooler & more efficently.

I agree with malevolent's write up Cool

I burnt my 800 watt Kingwin up running @ 740 watts for a month,it was 2 1/2 yrs old when I put it to mining.I didn't heed my rule & paid for it,nothing else was lost,got lucky.RMA went smooth as silk though.

Oh,Enermax is another good company I've used,but kinda pricey Wink

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December 21, 2011, 09:17:29 PM
 #5

You want to run a PSU at ~60% load for best efficiency typically.

If you're searching these lines for a point, you've probably missed it.  There was never anything there in the first place.
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December 22, 2011, 10:35:53 AM
 #6

It's tempting to use cheap PSUs but don't for this application. Even if you cringe about paying for a high end unit sit down and estimate how much you'll save per month by selecting one with >80%, >85%, >90% efficiency at the high Watt levels typical in this business.

My recommendation for cheap, good with 80+ efficiency when you can't afford Corsair AX or TX series is their Builder CX V2 series. Low cost, but still solid for sub 500W loads.

Compared to a cheap brand this one will save about $5/mo. anyway, so unless you plan to quit in a few months you'll end up spending more by buying cheaper.


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December 28, 2011, 10:13:59 PM
 #7

OK. I upgraded my main rig with a Corsair TX750 v2 and all is fine and nice.

Now let's come to my second rig:
Asus socket 939 with an Athlon64 single cpu, 4 ddr sticks, 2 sata 3.5 hdd, 1 radeon HD 5750 mining 24/7 @870/300
PSU: Amacrox warrior 500 http://www.amacrox.com/english/01_product/02_01detail.aspx?pdid=38

Question: I would like to add a second radeon 5750 or 6750, ideally not buying a bigger PSU at the same time (I would rather buy a new PSU some time later), could I do it safely (without starting a fire into my house)?

According the PSU calculator, currently my setup takes:
Minimum PSU Wattage:   283 W
Recommended PSU Wattage: 333 W * (including a 15% Capacitor Aging coefficient. PSU is 1 year old or little more)

If I add another 5750 the calculator says:
Minimum PSU Wattage:   338 W
Recommended PSU Wattage: 388 W*

The PSU specifics says that it supports up to 350W on the 12v line.
Thanks in advance for any informed opinion.

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December 29, 2011, 03:57:38 AM
 #8

You'd be pushing your luck, I think... probably won't set your house on fire, but it will probably kill the PSU sooner rather than later.

If you're searching these lines for a point, you've probably missed it.  There was never anything there in the first place.
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January 05, 2012, 08:19:52 PM
 #9

You want to run a PSU at ~60% load for best efficiency typically.
+1, I have been researching PSU curves, and it appears that between 50 and 60% load most of them have the greatest efficiency.
What this means to you as a miner is as follows:

With everything else being equal, using a higher wattage PSU can actually decrease your total power draw from the wall, sometimes by a decent margin.
So even though it may cost more, it also will pay itself off faster.

My current rig has 2 PSUs, 1 running a 50% load and the other at 60%. It draws less power from the wall than when I had just 1 PSU at 80% load.

Mining Rig Extraordinaire - the Trenton BPX6806 18-slot PCIe backplane [PICS] Dead project is dead, all hail the coming of the mighty ASIC!
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January 10, 2012, 03:44:32 PM
 #10

You want to run a PSU at ~60% load for best efficiency typically.
+1, I have been researching PSU curves, and it appears that between 50 and 60% load most of them have the greatest efficiency.
What this means to you as a miner is as follows:

With everything else being equal, using a higher wattage PSU can actually decrease your total power draw from the wall, sometimes by a decent margin.
So even though it may cost more, it also will pay itself off faster.

My current rig has 2 PSUs, 1 running a 50% load and the other at 60%. It draws less power from the wall than when I had just 1 PSU at 80% load.

While it is easy to make sweeping generalized comments (and the above from rjk and Inaba are not incorrect), you really need to do a cost-benefit analysis over the projected life of your miner.

Say you are drawing 600W. Buying a 1000W supply that is 5% more efficient (@60% load) than an 800W supply (@75% load) but costs $50 more will not be a good investment. Depending on your electricity costs, you may never recover that $50. A 5% higher efficiency @600W means you are saving 30W, or 720kWh/day. Assuming $0.10/kWh, you would need to run your rig for 700 days to make up for that $50. So in this case, it may be wiser to buy the less efficient supply

Any good 80PLUS Silver or Gold supply will have a relatively flat efficiency curve covering a very broad load range, so whether you load them at 40% or 80% doesn't make a large difference (you might see a 5-10% variance in efficiency within that range). Check the spec sheets of the PSU's you are interested in for efficiency-vs-load curves.

Do not ignore price. If you can get a 5% or 10% higher efficiency supply for not much more than a less-efficient one, it can be a good deal. But if you are paying $25 or $50 more for it, then it is worthwhile to do the math because you may find it will never pay for itself.

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January 10, 2012, 03:55:33 PM
 #11

True in and of itself, but you also need to factor in longevity of the unit.  Running a unit at 80-90% load 24/7 is going to burn that unit out much faster than running a unit at 50 - 60% load 24/7.  On a fair-middlin' power supply, I wouldn't expect a unit running 80% load 24/7 to last more than a year, probably less... whereas the same power supply running at 60% will likely fair much better.  So even a $50 cost bump may be warranted when you factor in the cost of replacing a burnt out PSU. 

Then you also need to factor in two additional issues:

1: Over time, your PSU is going to become less efficient and thus if you're already borderline, you may run into power problems causing miner instability, further reducing your income.
2: Future expandability as well as the fact that of all the components of a computer, except perhaps the case and monitor (and keyboard/mouse) - the PSU is the one that will need to be changed/upgraded the least often.  You can take a PSU through 4 or 5 iterations of a system, whereas nearly every other component is more "disposable" - so paying more for a PSU now will probably save you money down the road.

If you're searching these lines for a point, you've probably missed it.  There was never anything there in the first place.
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January 10, 2012, 04:16:46 PM
 #12

Agreed. Good points.

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January 12, 2012, 03:18:55 PM
 #13

Inaba covered it but I would add a couple points:

Good PSU tend to have longer warranties and PSU tend to hold their value (not like there is a next gen PSU 70% better coming out next month).  

So while break even might be 700 days on a $50 more expensive unit (which is probably closer to 1.5 years when you consider cooling costs) it likely has a 5 year warranty.  Even if you give up on bitcoin mining a solid well built PSU is something any gamer can appreciate.

I would also add heat affects PSU efficiency.  The curves drawn are usually for something unrealistic like 70F.  GPU are already dumping KW of heat into the room.  An 80% PSU loaded to 100W is dumping another 200W of heat into the room.  If you have 5 or 6 rigs you are now talking about a KW or more of EXTRA heat beyond the GPU.  The rise in ambient temp means the PSU become even less efficient.  Also if you are using AC to cool them every watt wasted due to inefficiency is going to cost you about 1.3W (1 watt wasted plus another 0.3W wasted to remove the heat you never wanted).

Once you get past a GH or so the largest barriers to large scale mining is power, heat, cooling.  The larger you get the more challenging it becomes.  Using inefficient or overloaded junk will really put a barrier on expansion.  If you intend to ever draw 2KW or more from the wall go for high efficient units.
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January 12, 2012, 09:40:22 PM
 #14

I use this PSU calculator.  http://extreme.outervision.com/psucalculatorlite.jsp  I've found it is unmatched in ability to mimic your system.

I use this website for PSU reviews.  Jonny is the best there is.  http://www.jonnyguru.com/

When in doubt just buy Seasonic.  There are a lot of companies that source their PSUs from Seasonic and they could be cheaper than the Seasonic models.
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January 13, 2012, 02:11:03 PM
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Jonny is very technically sound indeed but so are the hardware secrets guys (http://www.hardwaresecrets.com)
There is one aspect to PSU reviews where they are unmatched: they do crazy overload tests.
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January 13, 2012, 05:02:34 PM
 #16

I use this PSU calculator.  http://extreme.outervision.com/psucalculatorlite.jsp  I've found it is unmatched in ability to mimic your system.

I use this website for PSU reviews.  Jonny is the best there is.  http://www.jonnyguru.com/

When in doubt just buy Seasonic.  There are a lot of companies that source their PSUs from Seasonic and they could be cheaper than the Seasonic models.

+1 on the sea sonics..  I am up to 9 and counting!  (was getting the silverstones)

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