Choosing a Power Supply Unit at 12:23 PM

One main thing PC builders in Sri Lanka dont look for is the Power Supply Unit (PSU) for the system. Most of the time they just go for the PSU that comes with the casing. Its most probably a generic one that has something like 450w. When most buyers makes the budget for the system they dont even think of the price they are going to pay for PSU. Sometimes they build highend PC costing hundreads of thousand rupees and still got a generic PSU.But with todays highend pc components, its a must to have a good and stable power supply.

Lets think about the job of the power supply. It has to convert the Alternating Current that comes from the mains ( 230v) to the Direct Current (DC) that is used within the PC to power various components such as Motherboard, Processor, Disk Drives and Graphic Cards. Recently Graphic cards have been the main reason to have a good power supply unit. High end graphic cards need direct power from the PSU. Most of the time higher power is needed when processing 3d data such as games and animation rendering. If the supplied power from the PSU is not enough at that moment, PC would suddenly restart.

So we found that PSU does a very important job, so what to look for when buying a PSU ? First thing to do is calculate average power needed for your PC. That can be done using a online power calculator like following:

http://extreme.outervision.com/psucalculatorlite.jsp
http://www.thermaltake.outervision.com/

There you can get an idea about the needed power for a specific system, But this is not exact because sometimes level of power consumption depends on the brands of the products.For an example one brand of GeForce 9800GT will need more power due to its higher clock levels and high performance cooler. But getting an idea about the average power needed, you can get a PSU that is capalble of outputting more than needed power. Also in components like highend VGAs there will be notification of minimum power requirements of the product. So better see that and decide what PSU to buy.

Then choosing a PSU can be bit tricky because of some marketing manners of manufactures. Most of the time shops will know the Maximum power output of the PSU, thats like 400w or 500w. But thats not the whole picture and you cannot decide what to buy by just looking at that. Because many products here in sri lanka are not from reputable brands. Most of the time they will be some generic brand. Problem of that is their efficiency level is very low, so they will not output as expected. Displayed maximum power output (say 400w) is that PSU's peak output and it only output that power for VERY short time.

So when choosing you should have a rough idea of how power is divided within a PSU. For that you can check the label of the PSU. Mainly there are power output channels based on volts (called 'rails') of 3.3v, 5v and 12v seperately. So these rails will give different current outputs measured in Amperes(A) at that voltage lelvel.

But we must concern mainly on 12v supply as its the one most important to devices like VGAs. In that depending on the PSU and power output, there can be multiple rails of 12v, named usually 12V1, 12V2, 12V3.... OR 12Va, 12Vb, 12Vc .... but most of the time there will only be a single rail in cheap generic PSU. If it got multiple 12v rails, total power output can be obtained by adding the max Ampere levels of all 12v rails. For example if theres 2 rails with 12V1= 14Amp and 12v2= 14Amp then total is 28Amps @ 12v. But many cheap ones out there will have less than 18Amps in the one and only 12v rail.

So I will attach some pics of PSU labels with the specs.
Here is a 4 12v rail psu with 18Amp in each














This is a 550w psu with 2 independant 12v rails of 17Amp and 18Amp










Then theres the quality of power output issue, that depends mainly on the quality components like capacitors and ic used for the PSU. This is a factor you usually find by looking inside the PSU iself, but its not practical since you would have to buy it if you remove the casing of a PSU and that will also END your WARRANTY!!

So only thing you can do is to buy from a reputed brand for making good PSU. Especially if you are buying one for a high end pc (for gaming maybe? ;) ) its a very good idea to choose one from this. SOme of the companies are given below:
OCZ, Thermaltake, X-PRO, Enermax, Antec, Zalman, Seasonic, FSP, Corsair..

But in Sri Lankan stores they dont usually have most of these brands in stock. If you try to import them it might cost very high. So here are some of the good ones you can buy at Sri Lankan shops (or you can use a service like slmega to get them here) :
FSP
Amacrox (actually this is a brand from FSP company)
Asus
Thermaltake (not sure if anyone got these in-stock)


- - ADDENDUM - -

As at second week of Oct 2009,
there are
Amacrox 500s [500w] at about Rs 7000 @ eglobe(EGS), Barclays ....
FSP 300w at about Rs 2750+ @ EGS, Nunet ....
FSP 700w at about Rs 15 250+ @ EGS
Seasonic 650w at about Rs 15 000 @ EGS

check their online sites for more info:
www.eglobesl.com
www.barclays.lk
www.nunet.lk

This guide will be a work in progress, so will add/update in future.