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A Simple Explantion of a PSU

Last response: in Components
a b ) Power supply
January 29, 2012 4:37:20 AM

So this PSU thing, watts, volts, amps, rails, etc. Oh my god it's so confusing. I already read the articles on the forums and the articles within the forum topic. But Geez this PSU stuff is so confusing, if anyone can simply explain all the parts of the PSU and what they do, that would be great.

Oh and I got really confused when the article said something about having a 750w PSU that only submits 650w on 12v. I heard something with rails? What are rails? 12v rails? And there are different rails or something, 5.5, 3.3, 12?


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January 29, 2012 6:00:27 AM

ha, explaining all that wouldn't exactly be 'simple', i'd say they're the more complicated parts of a psu, if you google say, "understanding a computer power supply", you should wield some good results regarding this, also, i've found that various good reviews on psu's include some helpful information on different psu terms and whatnot.

if you're looking to buy a psu, then as long as u get the watts (500w, 750w etc), a quality brand, and make sure it has the right connectors, then you should be fine

i don't really know THAT much about all those psu terms but i know the basics and what to look for when looking for a good psu, but even then i look up a heap of reviews
a b ) Power supply
January 29, 2012 6:07:53 AM

simplest explaination is 'wikipedia'
thats all
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a b ) Power supply
January 29, 2012 7:03:46 AM

A PSU supplies several different voltages. in general all you need to worry about is the 12 volt supply, the others are rarely used and if your 12 volt supply is fine they will be too.

When someone says a 750 Watt supply only outputs 650 Watts at 12 volts that's exactly what they mean. Basically some lower quality manufacturers will add the other voltages in. So it may. be labeled 650 Watts on the 12 volt supply and 100 Watts on 5 volt. A good manufacturer will generally have the 12 volt supply able to deliver all 750 Watts at 12 volts. In addition some will make a supply, label it as 550 watts and it will burn out at 400 Watts. so badically they lie. they may also have issues with power quality, efficiency, and voltage regulation which can cause system problems. the protection circuits can also be low quality which means if it Burns out it can take other components with it. So it is very important to go with a quality manufacturer. OCZ, seasonic, corsair etc. there are also professional reviewers who fully test them till burnout and take them apart. jonnyguru and hardwaresecrets are two.

As for "rails" these came out of an outdated safety standard, bad marketing departments, and crossfire/sli. a PSU only has ONE 12 volt supply. What they do is they put a several current limiters in between the groups of wires and the supply to break them into groups. Current is your amps. so the 12 volt supply may be 600 Watts. volts x amps = Watts. so the total 12 volt supply can handle 50 amps. to get the "rails" they might create 3 groups of connectors limited to 20 amps each. Usually this would be the motherboard supply, and two connections for graphics cards.

Now, they do this so they can one up eachother in the number of rails or say "3 20 amp rails" etc in marketing. This is dishonest because if you add up the rails its far more than what the supply can deliver. Its also a pain to use because you have to keep track of what is in what rail, and you can run into situations where you have to split a GPU across rails, or you have enough power, but the rails artificial limits prevent you from using a GPU.

There's also 80 plus ratings. the higher the rating the less power is wasted and turned into heat in the PSU, and the lower the electric bill. in general 80 plus bronze is good enough for most people unless its going to be on and under load 24/7.

So in short, you want a good highquality brand, you want to check reviews, you want a supply that has a SINGLE high current 12v rail that ideally is rated at the same or close to the same as the actual PSU rating, and want it to be 80plus rated. And of course want enough wattage for your system. That can vary a lot depending on other components and future proofing, and is a common question which people will be happy to help you with in the forum.
a c 111 ) Power supply
January 29, 2012 7:08:14 AM

A psu gives your computer power so you can turn it on! ;) 
a b ) Power supply
January 29, 2012 12:20:28 PM

The different rails, are different sources of power for you computer. Even a single rail +12v system still has "different rails", since there are other voltages provided (5v, 3.3v etc). You can think of it like the power to your house. You have a breaker box (or fuse box if its an old house). The rails are like the different breakers in your breaker box. A single rail unit has fewer breakers that take more current to trip, while the multi rail units have more breakers that are rated for lower amounts.

Most of the things you will be concerned with run off the 12v line. Whether or not your PSU has 1 or many 12v lines can effectively be ignored. You should be more concerned if the unit is made by a good manufacture.

The total power output of your 12v line is going to be less than the total output since the other voltages (5v, 3.3v, etc) get added into the total W rating of the PSU.

Just to re-iterate. It does not matter whether the unit is a single or multi-rail psu. What matters more is that the unit is made well.
a b ) Power supply
January 29, 2012 4:43:11 PM

Ok so multiple rails do not matter? Are there any differences or advantages/disadvantages of multiple rails? I guess there really isn't a simple explanation of a PSU :/ 
a c 104 ) Power supply
January 29, 2012 5:02:49 PM

I don't know how much of this

you've read but there is a section on the multi 12v/single debate in there,
if you are stuck with options/choice, let us know what you are powering with your intended purchase, overclocked or not, and we can suggest a suitable Psu, and explain why we chose that one
personally though, I look at the amps on the 12v and check jonnyguru's review site for possible psu buys
a b ) Power supply
January 29, 2012 8:30:16 PM

Best answer selected by e56imfg.
a b ) Power supply
January 29, 2012 8:30:42 PM

I got it now :D 
a b ) Power supply
January 29, 2012 9:09:09 PM

This topic has been closed by Mousemonkey