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How to calculate the +12v rails?

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April 27, 2007 5:58:08 PM

Hi,

I've read PSU 101&102 but I don't understand how can I know the +12v rails on some PSU. most of the manufactures don't note the maximum wattage of the rails nor the total amperage on them.

For example I'm considering the HEC WIN 550UB or the HEC ACE 580UB but they only list the maximum amperage of each on of the +12v rails and not the combined...

Appreciate the help
Uri

BTW I gave HEC as an example because of the nice price tags, does anyone have experience with them? Are they reliable?

More about : calculate 12v rails

April 27, 2007 6:01:41 PM

speedfan ggogle it and download it is free
on the bottom left of speedfan it show the volts on the 12+
April 27, 2007 6:06:09 PM

But I don't have the PSU I'm trying to decide if I should buy it...
Related resources
April 27, 2007 6:30:34 PM

Quote:
Hi,

I've read PSU 101&102 but I don't understand how can I know the +12v rails on some PSU. most of the manufactures don't note the maximum wattage of the rails nor the total amperage on them.

For example I'm considering the HEC WIN 550UB or the HEC ACE 580UB but they only list the maximum amperage of each on of the +12v rails and not the combined...

Appreciate the help
Uri

BTW I gave HEC as an example because of the nice price tags, does anyone have experience with them? Are they reliable?


Buy a real PSU that has proper filtering and regulation and only ONE 12 volt rail and you won't have to worrie about the poblem.

You will however pay more for a proper PSU but you get what you pay for.
I would never use any of the many units that are popular with most readers.
April 27, 2007 6:40:43 PM

The honest companies list the maximum amperage on the combined 12v rails. Other companies are deceptive with their labels indicating only the maximum amperage on each rail and expecting you to add them up.
They really can't just be added up. There is no way for us to know the maximum amperage on the combined 12v rails without the manufacturer indicating it.
April 27, 2007 7:02:30 PM

I recall HEC being Antec's primary OEM many years back - I have a 300w unit that is well over 8+ years old powering my dual PIII-1ghz linux workstation/server, 24x7 for the past 2+ years w/o issue. Hopefully they didn't cheap out.

I did find a review of the WIN 480UB but it is more of an analysis than a load-power test. So apparently they didn't cheap out so that is good.

I do find the lack of manufacturer specs disturbing - however you can estimate to some degree the power the +12v can handle. I was able to find the label for the 550w in question:

So we have a total 550W and a +5/+3.3 max of 240W 8O wow that is high.

The non-primary rails can be subtracted (-12v*1a=12w, +5vsb*2.5a=12.5w) or 24.5w total
so the +3.3/+5/+12combined total = 550-24.5=525.5w

The minimum +12v capacity is 525.5w-240w=285.5w/12v=23.8A

Since the +12v is not independently regulated (meaning the max +12v is dependent on the +3.3/+5 combined load, which will be nowhere near 240w) a typical load will be ~80w to ~100w depending on the mobo components and the # of dimms and the voltage they run on and any PCI cards in the system.
525.5w-100w=425w/12v=~35A

However the question remains, how stable the +12v under such a high demand. That is what cannot be said with any determination.

edit - removed "stolen" image :twisted:
April 27, 2007 7:07:42 PM

try reading this
"http://www.pcpower.com/technology/myths/"

or this
"http://www.xbitlabs.com/articles/other/display/atx-psu5..."

i lived in area thats has 32 C ambient temp all year, so my psu reaches around 45 - 50C operating temp. before my current psu i used some cheap 600 watt psu (cameroon), i calculated my system need 270 - 380 Watts ( you could find the calculator here "http://www.extreme.outervision.com/psucalculatorlite.js..." ), at that time, I could not play medium games more than 15 minutes, even worse if i enabled all the graphic options to maxx, i could only hang on for 5 minutes before my pc rebooted.

Bottom line is, you need to know how much your system are consuming. cheap psu manufacturer list their max wattage at 25 C ambient temp, wich will never hapen to most of us, unless winter is the only season you got.
so if you system would only consume about 200 watts, 500 watt cheap psu would be enough for you... if you need 300 watts then its 650 watt.
if you more then that, i suggest you buy a better if not good quality psu.
April 28, 2007 9:12:12 AM

That's what I thought... :(  Do you know how much reliable HEC are?

And what can I conclude from the fact that the combined +5 and +3.3 are 240W?
April 28, 2007 12:03:16 PM

Quote:
Do you know how much reliable HEC are?

Check out the hardwaresecrets.com article on the 480w I previously linked to, it explains, in a nutshell, that they use unusually high quality components for a budget unit.

Quote:
And what can I conclude from the fact that the combined +5 and +3.3 are 240W?

sigh... Ok I will help you out - same article quote, answer in bold...

Quote:
HEC WinPower 480 W Power Supply review, hardwaresecrets.com"]The +12 V output is produced by two MBR20100CT Schottky rectifiers, which can deliver up to 20 A each (measured at 133º C), thus the maximum theoretical current the +12 V line can deliver is of 40 A, which equals to 480 W. The maximum current this line can really deliver will depend on other components, especially the transformer, the coil, the capacitor, the wire gauge and even the width of the printed circuit board traces used.

The +5 V output is produced by one MBR6045PT Schottky rectifier, supporting up to 60 A (measured at 125º C). This equals to 300 W. Of course the maximum current this line can really deliver will depend on other components, especially the transformer, the coil, the capacitor, the wire gauge and even the width of the printed circuit board traces used, as mentioned before.

Here we found something different from other power supplies with no PFC we’ve seen so far. Usually the +3.3 V output on low-end power supplies is done by a 3.3 V voltage regulator connected to the +5 V output. This power supply from HEC, however, uses the same design as high-end power supplies, using an independent Schottky rectifier for producing its +3.3 V output. Even more: on this power supply we could notice a place for installing a second rectifier in parallel, doubling the amount of current supported by the +3.3 V output. This configuration is probably used by another power supply manufactured by HEC based on the same PCB used by WinPower 480 W.

The +3.3 V output is produced by another MBR6045PT Schottky rectifier, supporting up to 60 A (measured at 125º C). This equals to 198 W. Of course the maximum current this line can really deliver will depend on other components, especially the transformer, the coil, the capacitor, the wire gauge and even the width of the printed circuit board traces used, as mentioned before.

Even though the +5 V line and the +3.3 V line have separated rectifiers, they share the same transformer output. So the maximum current both lines can deliver will depend a lot on the transformer.

This power supply uses Taiwanese electrolytic capacitors from Teapo and CapXon. The two big capacitors from the voltage doubler are rated 85º C while all other smaller capacitors are rated 105º C.
[/url]
This explains the unusually high +5/+3.3 combined wattage.

They also mention the acepower 480 is identical internally to the winpower so that is reassuring the component selection will be similar.

This is interesting...

Quote:
HEC AcePower 480 W Power Supply review, hardwaresecrets"]...the manufacturer’s honest statement on the product manual explaining that this power supply is labeled at 40º C and that above this temperature the power supply maximum output power should drop 1% / º C.
[/url]
Honesty is the best policy, and its not 25ºC like other budget brands. Then again, if all this info is not over your head, you already realized this is not a typical budget unit.

Hey, I found a review over at extremeoverclocking...
Quote:
HEC ACE Power 480W Power Supply review, extremeoverclocking"]Comments:

* Good voltage regulation
o +12V rails stayed +1% or better
o Other rails generally stayed above nominal.
* Good efficiency, ~80% under typical load.
* 12V Rails loaded each to ~17.5A, voltages still stayed within 2% of tolerance.
* Dual 80mm fans were very quiet, even under heavy load
[/url]
They loaded this unit at and above the per-rail maximum rating? 8O And it remained within 2% spec?? 8O 8O
April 28, 2007 12:30:23 PM

Quote:
So you wouldn't be able to subtract the 3.3v/5v wattage from the total wattage to get what you need for the 12v rail.

Yes, you can. The total really is equal the sum of it's parts, when you know the right values.
Quote:
...you have no way of knowing the total amperage of the +12v rails.

The best you can do is make an educated guess. The more you know, the more accurate you can get.

I am surprised I have to explain this...
April 28, 2007 2:03:27 PM

Same rules apply, all the info is still there you just have more to work with - hence you get a more accurate picture of what the unit is capable of. You are 100% correct, you can't just sum up everything - something has to give. Just think of it as trying to figure out what is going to give under different scenarios.

Let's use the two examples you have provided:

Enermax
477.8w=+3.3/+5/+12 combined
If +3.3/+5@160w, then +12max = 478w-160w=318w/26.5A
Conversely, if you +12@384w, then +3.3/+5max = 478w-384w=94w

Corsair
520w-(9.6w+15w)=495.4w=+3.3/+5/+12 combined
If +3.3/+5@140w, then +12max = 495.4w-140w=355.4w/29.6A
Conversely, if +12@480w then +3.3/+5max=495.4w-480w=15.4w 8O not a whole lot of room when the +12v is running max...
April 29, 2007 4:15:01 AM

enermax liberty:
although the DC output states 22A per rail but, in reality it only can output max 32A for 12 volt

Corsair HX520 W:
although the DC output states 18A per rail, but in reality it only can output max 40A for 12 volt. the corsair unit states that it have been tested to be used in 50C workload temperature. you can find it in their website

and oh, you could only use the max amp just for under 1 minutes before blowing up the psu( on a cheap generic psu ), or the psu just reboot.

Theres another catch, due to the recent problem in modern modular psu, now all the new psu although states have multi individual 12 volt rail, but in reality the rail were just combined in the psu itself
quoted from "http://www.xbitlabs.com/articles/other/display/atx-psu5..."
Quote:
So, when it became necessary to push the allowable current bar higher on the +12V rail, Intel Corporation, the developer of the ATX12V standard, decided to divide that power rail into multiple ones, with a current of 18A on each, the 2A difference being left as a small reserve. Purely out of safety considerations, there was no other reason for that solution. It means that the power supply does not necessarily have to have more than one +12V power rail. It is only required that an attempt to put a load higher than 18A on any of its 12V connectors would trigger off the overcurrent protection. That’s all. This simplest way to implement this is to install a few shunts into the PSU, each of which is responsible for a group of connectors. If there’s a current of over 18A on a shunt, the protection wakes up. As a result, the output power of none of the 12V connectors can exceed 18A*12V=216VA, but the combined power on the different 12V connectors can be higher than that number.

That’s why there are virtually no power supplies existing with two, three or four +12V power rails. Why should the engineer pack additional components into the already overcrowded PSU case when he can do with just a couple of shunts and a simple chip that will be controlling the voltage in them (the resistance of a shunt being a known value, the current passing through the shunt can be known if you know the voltage).

But the marketing folk just couldn’t pass by such an opportunity and now you can read on any PSU box that dual +12V output circuits help increase power and stability, the more so if there are not two but three such lines!
April 29, 2007 4:19:27 AM

uri, specify your spec the quantity of your hdd, fan, cd, dvd etc, so we could just determine if your HEC psu were enough for you.
April 29, 2007 12:00:21 PM

well... I'm planning a build for when I finish this semester so I don't have the specs yet but it suppose to be something like:
CPU: e6420 + Freezer 7 PRO
MB: Abit AB9 Pro
RAM: 2x1GB DDR2-800
GPU: 8800 GTS320 (or if the HD2600 will be any good :D  )
That's about it (of course with an HD, DVD, etc...)
and since I tend to buy a PC once every 5 years and just upgrade it (GPU, more HD...) I would like to have a little extra power so I won't be very limited by the PSU
April 30, 2007 4:41:05 AM

well, based on the specs, i presume your system need would be from the 250 to the 400 watts ( depends on how much fans and hdds you were using )
based on that your choice of hec 550 or hec 580 would not be enough, you need something higher

HEC 550 : 5V and 3,3V combined 240 watts
so 550 - 240 = 310 /12 = 25 Amps total of 12V
HEC 580 : 5V and 3,3V combined 240 watts
so 580 - 240 = 340 /12 = 28 Ams total of 12 V

if you weren't planning of using to much fan, hdd, or dvd drives, i'll say HEC 580 were just enough without having any more spare left when you were playing games.
also if you were planning to use it for at least 5 years, better if the psu have 5 years guarantee...
as mpilchfamilysays
[/quote]Well if you want to be future proof then you need to look at more qualtiy PSUs
Quote:

April 30, 2007 12:47:43 PM

Quote:
HEC 550 : 5V and 3,3V combined 240 watts
so 550 - 240 = 310 /12 = 25 Amps total of 12V
HEC 580 : 5V and 3,3V combined 240 watts
so 580 - 240 = 340 /12 = 28 Ams total of 12 V

This is the minimum +12v power since you assumed a maximum +3.3/+5 load of 240w in that calculation. See my previous post for a more accurate description of what the unit is capable of.

Quote:
i'll say HEC 580 were just enough without having any more spare left when you were playing games.

I disagree, since extremeoverclocking.com pulled +12v@35A/420w from the HEC 480 in their load test... suprisingly close to what I calculated the 550w to have. Maybe I underestimated... I would have no problem putting the 550 or 580 (or the 480 for that matter) in my 8800gts game rig w/o a second thought.

I own an Antec 300w server pull that is HEC built. It is 8+ years old and it's running my linux workstation 24x7 for the past 2 years, the only thing I replaced is the 80mm fan.
They are obviously doing something right. I say they have a very strong price/performance, and provided enough links to back it up. I will agree, it is simpler to bash them and say HEC is not good without an intelligent analysis. IMO the acepower/winpower series appear to be server grade units with cheaper caps, and for the price may be a better choice than the Rosewill RP550-2 since it has higher power capacity. The only other budget unit that I know of that can compete is the epower ZU-550 which boasts +12v@38A, but having personally used this unit the voltage is not as stable (but within specs).

Conversely, when a quality unit like the Corsair 520w can be had @ buy.com for $99 shipped w/ $20 MIR that is a tempting purchase indeed - practically self-justified with the rebate to front the extra $$.
April 30, 2007 12:58:15 PM

doolittle wrote
Quote:

Conversely, when a quality unit like the Corsair 520w can be had @ buy.com for $99 shipped w/ $20 MIR that is a tempting purchase indeed - practically self-justified with the rebate to front the extra $$.

Unfortunates for me the prices here are a bit different, the Corsair is ~170$ US and the HEC is ~100$ US :( 
So you can see why I'm looking at budget PSU...
April 30, 2007 3:55:05 PM

Based on your setup, and some mpilchology from the PSU 101/102 sticky I guesstimated your combined +12v to be around 21A at most with an 8800gtx card. Either of those HEC units should be able to handle that without issue.

A quick google search shows several various forum user's specs to show an HEC paired with the 8800gts, so that maybe worth a look - maybe reg on those respective forums and ask them what their experience has been with them since we are just speculating at this point. I was surprised to see that much information available from the reviews I have found on the 480 model, and based on that the unit seems to be well constructed beyond typical budget units in that price range.

Weather or not it will last 5+ years is a difficult prediction, if you have a UPS unit and/or relatively clean power in the utility grid it will help but the question is - will the capacitors take well to aging... IMO if you take care to keep the case temps to a reasonable level, the power supply will not overheat too badly and the caps will not age prematurely, that is the best you can do with budget units. 5+year warranty can only be provided by the best component selection, used in expensive power supplies such as PCP&C and Corsair - a budget unit may last as long but the component yield is not as strong so not guaranteed... HEC from what I recall is 1 year only. That is not to say it will not last up to 5 years, but you just won't get a free replacement. Conversely, I have seen quality PSU's having to be replaced as well so it is convenient to have the warranty to fall back on. What is difficult to bear in that case, is waiting for the manufacturer to RMA so a spare is handy for the interim replacement period :wink:
April 30, 2007 4:33:23 PM

Quote:
But I don't have the PSU I'm trying to decide if I should buy it...


If the vendor you're buying from can't provide you with those specs, I would seriously considering finding a new place to buy from... and if the manufacturer doesn't list those specs on its web site... the same applies.
April 30, 2007 9:06:19 PM

doolitle, i may not be very clear about this, but all i'm saying is if uri decides to add couple more peripherals to his system, like more hdds, 3 or more fan, another dvd, or even lighting the case... well i think that woudnt be enough.

i didnt say you should buy the corsair, the cheaper and the most quality is what you should get, and people has lot's of different opinion, budget, logics on things.. so well leave that to you, we were just trying to gave you insight of what you should get.

just put into consideration of what mpilch, doolittle, rodney or even ZOldude
Quote:
You will however pay more for a proper PSU but you get what you pay for.
I would never use any of the many units that are popular with most readers.
says

doolittle : yeah, i was just a bit to the safe side, in case uri decides to buy the budget ones, at least with bigger wattage, his psu could run longer with only light to medium load. that was all i'm thinking. you surely don't want to stress your psu up to 70 - 80 % at idle all the time do you??
Quote:
Weather or not it will last 5+ years is a difficult prediction, if you have a UPS unit and/or relatively clean power in the utility grid it will help but the question is - will the capacitors take well to aging... IMO if you take care to keep the case temps to a reasonable level, the power supply will not overheat too badly and the caps will not age prematurely, that is the best you can do with budget units. 5+year warranty can only be provided by the best component selection, used in expensive power supplies such as PCP&C and Corsair - a budget unit may last as long but the component yield is not as strong so not guaranteed... HEC from what I recall is 1 year only. That is not to say it will not last up to 5 years, but you just won't get a free replacement. Conversely, I have seen quality PSU's having to be replaced as well so it is convenient to have the warranty to fall back on. What is difficult to bear in that case, is waiting for the manufacturer to RMA so a spare is handy for the interim replacement period Wink
!