PSU basics.. help!

look at this

I just don't understand why the total watt is 480watt and not 671watt. (3.3V*30a)+(5V*35a)+(12V*17a)+(12V*16a)= 671W

they are using dual 12V rails shouldn't we take that into consideration?

and they said the combined 3.3V and 5V is 220W. so when i calculate the 3.3V and 5V rails it comes to 275W. whats happening?

thats probably because the 480 watt is the power supply's rated contant outpu while the 671 is possibly the most power it can supply for a short period. like when the computer is first powered up and all the motors in hdds and fans start. (motors can draw up to 300% of their rated current when they start)
just a thought, not sure though either ive never actually calculated the individual ratings on my supply.

Skeith said:

thats probably because the 480 watt is the power supply's rated contant outpu while the 671 is possibly the most power it can supply for a short period

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wrong, that's not the case at all

the ratings for each rail for example 5v at 35a means the maximum you can draw from that rail is 175w, you can't draw the maximum from all rails at the same time, only a combination up to 480w or at least they promise up to 480w, brands like fortron and antec usually do more than their rated

alot of good companys put the total max load on the 5 and 3.3V rails in watts for you on there website. this can give you a little more insite..

R4z0r4mu5 Pr|m3 said:

wrong, that's not the case at all

the ratings for each rail for example 5v at 35a means the maximum you can draw from that rail is 175w, you can't draw the maximum from all rails at the same time, only a combination up to 480w or at least they promise up to 480w, brands like fortron and antec usually do more than their rated

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so you're saying that if i have more amps taken from the 12V rail then the 3.3V or 5V will decrease in amps? this would mean unstable?\

damn i was planning for that HEC. good price and i like how they distribute the stuff in the 12V dual rails.

greenmaji said:

alot of good companys put the total max load on the 5 and 3.3V rails in watts for you on there website. this can give you a little more insite..

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sorry i didnt read this as i just posted...... but you are saying that if i that the total output which is 480W and minus the max load on the 5V and 3.3V i should get the watts distributed in the 12V rails? is this correct?

total on all other rails.. but 12V should be the main one
you have low amp - rails and sometimes another 5V

greenmaji said:

total on all other rails.. but 12V should be the main one
you have low amp - rails and sometimes another 5V

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didnt understand it.... but even looking at the antec 480watt neo. i calculated it should be 685W. so how safe can we be when calculating it.... how can i judge from this?

wait... it says that at full load the effiency is around 70%. and i calculated 685Watt X 75% = 479.5W... is this the way to calculate?

so by using this.. if i want to calculate the 12V rail i must multiply V with AMP and then multiply it with the effiency?

Rickster said:

so you're saying that if i have more amps taken from the 12V rail then the 3.3V or 5V will decrease in amps? this would mean unstable?\

damn i was planning for that HEC. good price and i like how they distribute the stuff in the 12V dual rails.

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the more you use from one rail, the less the other rails can provide but the number they give you for each rail is the maximum they promise that rail will support and the number they give you for the power supply itself is the maximum wattage they promise that power supply will provide, i don't know what you mean by unstable, this is how all power supplies work

Rickster said:

didnt understand it.... but even looking at the antec 480watt neo. i calculated it should be 685W. so how safe can we be when calculating it.... how can i judge from this?

wait... it says that at full load the effiency is around 70%. and i calculated 685Watt X 75% = 479.5W... is this the way to calculate?

so by using this.. if i want to calculate the 12V rail i must multiply V with AMP and then multiply it with the effiency?

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no, that's just a coincidence, you don't get 685w, you get 480w, the maximum on each rail isn't always provided but if you're not using so much power from other rails that it limits a rail, the maximum can be provided

efficiency is a different story, if you use the entire 480w at 70% efficiency, you are drawing 685.71w (480/70x100) from the wall with 30% wasted, this has nothing to do with the combination of maximal wattage each rail provides, again just a coincidence, efficiency is how much power from the wall you're actually using and how much you're wasting due to the power supply's electrical properties

oh i see. so really calculating the watts is like a guesstimate thing. no real way to calculate it exactly.

hmmm.... then what if the 12V(2nd rail) is the one supplying power to your PCI-e and theres a lack of power from that rail, will it pull some power of the 12V(1st rail)?

-----------edit-------------
something which is out of my topic title.... but im wondering.... do you guys think this PSU will fit for
7900GT
intel 3.0Ghz (630 90nm)
watercooling setup

im planning to overclock a little bit... no volt modding.

im guessing it will.

12v2 goes to the cpu and 12v1 goes to other components in dual 12v PSUs, if you are lacking power you will experience problems, each rail is limited to a certain amount of power, if you can have 15A on 12v1 and 15A on 12v2 in a PSU, you can't draw 30A on 12v2 and 0A on 12v1, you will be limited to 15A on 12v2 no matter what

there are ways to calculate watts if you have the right equipment and it can be very accurate, read some articles from tomshardware.com and silentpcreview.com and you will understand, without the PSU on hand you can't know specifics (remember each PSU is different, even of the same model which can be trusted to be very similar) and are left with what they promise you which is the total amount of power the psu can supply (ie. 480w) and what each rail can supply

that PSU looks ok for what you want to use it for, what other choices do you have? any sparkle/fortron, ocz, or seasonic psus available?

well i have these choices:
Enermax
HEC
Coolermaster (don't like coolermaster products)
ACBEL (seems to be sold in almost every shop)
Enlight
Tagan
Thermaltake
Antec
OCZ Modstream

I like that MEC psu. Its relatively cheaper than the others and the reviews sound good. The wiring is done so that
12V1 = 24pin, Peripherals, SATA
12V2 = PCI-e, 4pinATX

I think its good to separate the PCI-e from the 24pin. So it won't draw so much power from the same 12V rail. Seems good for its price. Thanks for your help. Atleast now I can intrepret the sepcs correctly.

Rickster said:

well i have these choices:

Enermax
HEC
Coolermaster (don't like coolermaster products)
ACBEL (seems to be sold in almost every shop)
Enlight
Tagan
Thermaltake
Antec
OCZ Modstream

I like that MEC psu. Its relatively cheaper than the others and the reviews sound good.

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Real reviews, like the kind Jonny Guru does, or reviews where a "full" load for a 500W PSU is just 200W and they get excited when the +5.0V rail fluctuates only .0001V? At the very least avoid HEC's Orion series, which is their worst and lacks even the EMI filter (empty spots on circuit board where its components normally go). All the PSUs I've seen that lacked EMI filters were junk.

Coolermaster seems to get its PSUs from at least two suppliers, ACBel Polywel and HiPro. AcBel is supposed to be OK, but in Tom's endurance test, a 550W model's +3.3V rail drooped to +3.09V. HiPro is sometimes very good, but I've read that their designs vary in quality.

I'd rather buy Antec, Enermax, or Enlight, provided it's still made by Enhance. My next choices would be OCZ (but if they're made by Fortron-Source, as the newer ones seem to be, they'd be among my first choices) and Tagen.

I would recommend Fortron (higher end), Sparkle, Enermax, Antec, OCZ (higher end) or Seasonic. While everyone has had one off-brand PSU run forever, you will see several recommendations for the above units versus the others in your list.

larrymoencurly said:

Real reviews, like the kind Jonny Guru does, or reviews where a "full" load for a 500W PSU is just 200W and they get excited when the +5.0V rail fluctuates only .0001V? At the very least avoid HEC's Orion series, which is their worst and lacks even the EMI filter (empty spots on circuit board where its components normally go). All the PSUs I've seen that lacked EMI filters were junk.

Coolermaster seems to get its PSUs from at least two suppliers, ACBel Polywel and HiPro. AcBel is supposed to be OK, but in Tom's endurance test, a 550W model's +3.3V rail drooped to +3.09V. HiPro is sometimes very good, but I've read that their designs vary in quality.

I'd rather buy Antec, Enermax, or Enlight, provided it's still made by Enhance. My next choices would be OCZ (but if they're made by Fortron-Source, as the newer ones seem to be, they'd be among my first choices) and Tagen.

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lol... I wasnt going for the orion series. They don't even have it in Malaysia. Im planning for this. MEC ace 480watts. Review looks good. Maybe I should look at reviews on tomshardware too.